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轉載自天蝎之巢:Windows編程中SetViewportOrg與SetWindowOrg的理解
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最近突然又很有激情的開始看Jeff Prosise的那本"Programming Windows with MFC, 2 ed."。盡管是英文版的，但是感覺這本書上手比喉結的那本所謂的深入淺出MFC 要容易理解的多。候同學給人一種故弄玄虛故作深沉的感覺，而Jeff Prosise的這本書才真正的稱得上是深入淺出。

盡管如此，其中有關GDI繪圖中的坐標映射部分還是有一個問題沒有搞清楚，那就是SetWindowOrg和SetViewportOrg這兩個函數到底應該如何理解。潘愛民翻譯的那本VC內幕沒有講清楚；Jeff Prosise的這本書沒有講清楚；MSDN上的東西看的也是一頭霧水；Charles Petzold的那本書還沒有來得及看。因為這個問題，昨天晚上是帶著遺憾的困惑入睡的。

總的來說，我對這兩個函數的理解導致的結果是與實際程序運行的結果截然相反。依據MSDN上的解釋，有一個很嚴重的問題沒有闡述清楚，那就是：所謂的SetWindowOrg(x, y)函數，到底是表示set window origin to (x, y)還是set window origin as (x, y)；to和as在執行的時候，其操作的效果是截然相反的。

set window origin to (x, y)表示將坐標原點設置到(x, y)；即以(x, y)作為坐標原點，此時原點坐標不再為(0, 0)；
set window origin as (x, y)表示將原來的原點(0, 0)的坐標改為(x, y)；即將所有點的坐標增加(+x, +y)；

現在我的理解是：應該是 set window origin to (x, y)。這種理解基于以下幾個前提：
1. 所有繪圖語句中給出的坐標，全部是邏輯坐標，即在 window 中的坐標(相對于viewport所表示的設備坐標而言);
2. 所有用戶能看到的點，其設備坐標一定是位于(0, 0)和(1024, 768)范圍內；(假設顯示器為輸出設備，采用MM_TEXT映射方式，且屏幕分辨率為1024*768);
3. 所謂“(0,0)就原點，原點的坐標一定就是(0,0)”這種理解，是錯誤的；
4. Viewport中的坐標表示設備坐標；Window中的坐標表示邏輯坐標；
5. 當在邏輯坐標中指定新的原點后，在執行映射時，設備坐標的原點一定要與邏輯坐標的新原點重合；反過來也是一樣，即兩個坐標系的原點一定要重合。

(1)
CRect rect(0, 0, 200, 200);
dc.rectangle(rect);
上面的語句在屏幕的最左上角繪制一個正方形;(因為此時邏輯坐標與設備坐標沒有偏移)

(2)
dc.SetViewportOrg(100, 100);
CRect rect(0, 0, 200, 200);
dc.rectangle(rect);
將設備坐標的原點設置到(100, 100)；即設備坐標的原點不在(0, 0)處，而是在(100, 100)處；此時若執行映射的話，邏輯坐標的原點(0, 0)需要與設備坐標的原點(100, 100)重合(參考前提5)；那么此時繪制的矩形(0, 0, 200, 200)的坐標(為邏輯坐標，參考前提1)在設備坐標中就會映射為(100, 100, 300, 300)，最終我們在顯示器上看到的會是一個向右下方偏移(100, 100)的一個邊長為200的正方形(用戶看到的點是在設備坐標中的，參考前提2)

(3)
dc.SetWindowOrg(100, 100);
CRect rect(0, 0, 200, 200);
dc.rectangle(rect);
將邏輯坐標的原點設置到(100, 100)；即邏輯坐標的原點不在(0, 0)處，而是在(100, 100)處；此時若執行映射的話，設備坐標的原點(0, 0)需要與邏輯坐標的原點(100, 100)重合(參考前提5)；那么此時繪制的矩形(0, 0, 200, 200)的坐標(為邏輯坐標，參考前提1)在設備坐標中就會映射為(-100, -100, 100, 100)，最終我們在顯示器上看到的會是一個只有1/4個大小的矩形的一部分(事實上相當于向左上方偏移(100, 100)的一個邊長為200的正方形。注意：用戶看到的點是在設備坐標中的，參考前提2)

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美國人掛在嘴邊的句子

作者: Jerry Cat
時間: 2006/07/09
鏈接: http://www.shnenglu.com/jerysun0818/archive/2006/07/09/9611.html

Though you may tell someone they are doing something in a wrong way, you have to stop criticizing them if their method works.

Like money in a savings account, success seems to compound itself. A person who has a small success expects it to be followed by a bigger one.

It does not matter how you succeed. Any method is all right if it works for you. This proverb is not always accepted. Often one hears the opposite, " the end doesn't justifies the means."

If you cannot compete successfully with a person or a group, stop competing and go join them. Then you can share in their success.

A criticism of a person who never succeeds. The failures may not be drastic but the pattern of small failures is annoying to others, especially in two areas that Americans value as highly as time and money.

Concentration leads to success. The person who tires to do too many things at once may fail at all of them.

We will not discuss or worry about a future problem. If and when the problem becomes urgent, we will deal with it.

Do things in a sensible order. For example, do something to impress your boss before you ask for a raise in pay. Don't ask for the raise first.

Do not trust a rival or an enemy at all. His or her desire to succeed will overrule everything else. Such a people may lie, cheat, attack or do many other things far more terrible than he or she would normally do.

Flexibility leads to success in unfamiliar circumstances. People may changes their normal way of doing things in order to fit in better with those they are visiting.

Some things require gentleness for success. One should not push too hard. Force may cause damage

Do not be discouraged by the size of your problem or the fame of your competitor. (the saying is traced to a boxer preparing to fight an opponent much larger than he was.)

If we can come to a successful conclusion, let us forget about the pain and mistakes along the way.

Go ahead and try to achieve your goal. Don't worry about failing. Similar to this proverb--God provides food to every bird, but he won't cast to its nest, you got to earn it.

If someone apologizes for giving only a small gift, the recipient may encourage the giver by quoting this proverb. This is especially true if there is a huge job to do or a huge amount of money to be raised from many people.

"Fool's gold " is the popular name for a kind of stone that glitters like gold but contains no gold at all.

Do not ask too many questions or become too curious about things. You may get yourself into trouble like a cat that does not see the danger in a new situation.

Do not risk everything in one place or on one project. Divide your sources that one failure will not ruin you. Similar to this proverb---Do not use both feet to test the depth of the river.

This is often used to warn about advertising. An offer looks good but turns out to be misleading.

If flattery (insincere praise) is recognized, it will not succeed. One sometimes hears the opposite, Flattery will get you everywhere.

If someone you do not know offers you a free lunch or other gift, watch out. The gift may be a method of getting something from you.

Do not be over-confident and careless. Your circumstances may change quickly and the emptiness of your bragging will be exposed.

One may enjoy the process of playing a game whether one wins or not. This traditional proverb is now often heard in the opposite form, Winning isn't everything. It's the only thing!

Wait and see how something will work out. Don't trust a person or thing too much right now.

Some of life's lessons are learned the hard way. The person who has had to pay for a mistake will be careful not to make that mistake again.

There are opportunities! For example, this may be used to encourage someone who has just broken off a relationship with a sweetheart.

Do not become too confident of success before you can see that progress is happening.

Do not be discouraged if your goal still seems far away. On a big project, success takes time!

Be careful. People are hiding something in order to protect themselves or take advantage of you.

Businesses instruct their clerks not to do anything that might threaten a customer's self-esteem, no matter how unreasonable the customer is. Any complaint of any customer must be carefully and politely heard by any employee. The customer must not be made to feel ignorant.

Do not compromise yourself or your beliefs in order to please other people or fit in with a system. Know who you are. Let other people know what you stand for. Do not give in to pressure to conform or to do things you do not agree with.

This may be used to explain the behavior of a person who is overly cautious about something. The wise person makes mistakes but does not usually make the same mistake twice.

I refuse to admit defeat yet. Though right now it looks like I may fall, there is still time for things to change. (The "fat lady" is an insulting reference to an opera soloist, opera often end with a female solo.)

Each individual should be allowed to have his or her own preferences. people will naturally choose different activities, goals, life-s, etc.

Looking out for one's own personal welfare more than anything else. This is sometimes used to criticize a person who has abused or taken advantage of someone else, "All he was doing was looking out for number one." Or it may be used to defend himself or herself, "There is nothing wrong with what I did. I was just looking out for number one."

When situation is difficult, only the determined people can handle it. They don't give up!

A day seems shot when it is full of enjoyable things but it seems like an eternity if one is idle or stuck with a boring job.

Live according to your desires at the moment. Forget about rules, regulations or consequences. Just have fun.

Variety is what makes life pleasureable. Boredom is seen as a threat and monotony is the surest route to boredom.

Wealth has influence. People who make big contributions to political candidates are "talking" to the candidates and expecting them to listen.

This is used to criticize someone who takes work too seriously. It affirms that play is as an essential part of human life.

This is a way of welcoming someone to participate. It means, the bigger the group, the bigger the party.

A thing you already have is worth twice as much as a thing you might get in the future.

Make up your mind. Sometimes one must choose between two very desirable things, giving up one thing in order to enjoy the other.

Any of several methods may bring about the desired result. Each person may choose the method that best suits her. If one method does not work, choose a different one and try again.

Since the same thing may affect different people in different ways, each person must choose the things that will work in his or her particular case.?

Love is considered one of the most powerful and determined forces in the world. Two people in love will "find a way" to get together.

When lovers are separated, they may think about each other constantly. their love may deepen.

This is said of someone not considered important or worthy of loyalty. One forgets about that person as soon as he or she is out of sight.

Love is the driving force in all of life. Love makes life worth living. If you understand love,you understand everything about life.

Do not rush into any long-term commitment. In the past this meant, "take your time before you commit yourself to a marriage partner." Now it means, "Do not commit yourself to anyone you will be sorry." or it may mean, "Live with a person for a while before marrying him or her." It may also apply to any long-term partnership, such as a joint business venture.

Talking is not doing, It is easy to talk about a plan, but this gets little respect untill one takes a risk and puts the plan into action.

Time can be converted to money, that is, wages are often paid per hour of work. Managers want employees to do things quickly because "time is money." If employees waste time, the company loses money.

This question implies that intelligence, like time, can be converted into money. It is used to cut down an ordinary person (not a rich one) who has expressed an opinion as if it is the final word on the subject.

Beggars have to accept whatever they get. A poor person has very few choices in life. This harsh reply may be used if people complain about the size or quality of a gift.

Greed will lead a person into many other evils such as cheating, oppression and violence. (one also hears, money is the root of all evil, which places the blame more on money than on greed.)

Folly will always show up in the way a fool handles money. Wise people are the ones smart enough to guard money once they have it.

Playing well and fairly is more important than succeeding. This saying is sometimes used to console someone who has lost a game. The ideas is that in spite of losing, one may still feel like a success if one has played as well as possible.

There are some things money just can't buy. This reminds people that money is not an ultimate value although it often is treated as one. The saying may be used as a comment when a wealthy but lonely and wretched person commits suicide.

Success is valued more highly than kindness and politeness. If unkindness and impoliteness contribute to one's success, they are sometimes excused as "toughness" or "what it takes." This is more often applied to men than woman.

This recent, cynical saying makes fun of three common American desires-- competing, accumulating property, and having fun.

This proverb is actually a recently invented advertising slogan for the Nike Shoe company. It may also be the best three-word summary of American cultural values. It means, "quit being indecisive, Don't bother consulting a lot of people. Don't waste much times on planning. Just do it and do it now.

Get serious about what you are saying. When you have spoken in favor of something, prove that you mean it by risking some money on it in a bet or an investment.

Be pro-active and goal-oriented, not timid or conservative. Aim to conquer, not merely to protect yourself.

Like talking, intending is not doing. Actions matter far more than intentions. Actions determine where a person ends up.

When people have nothing constructive to do, they get into mischief. The child who is bored may pick up a crayon and color on the wall, something that would not happen if the child were happily occupied in some other activity.

Grab directly and fearlessly for the toughnest part of a problem. Don't look for an easy way out.

If you have received something without working for it, it may soon be gone. You will not be as careful with it as you will be with something you earned.

Individual action or action by the smallest group possible is better than consulting a lot of people. Too much consultation will waste time and create problems.

Grow up; act like an adult. Don't ask me to do something for you. This may be said to a young or immature person who depends too much on others. It is like a cow kicking a grown calf that wants to suckle.

This discourages people from trusting anyone except themselves. It maybe said to someone who ask another person to do a job for him/her and then complains about it was done.

When a person really needs something, he or she figures out some new way to get it. This creative initiative to change one's situation is considered much better than giving up and accepting things as they are.

This saying is used when there is a limited supply of something such as tickets to an event or food at a picnic. The idea is that no matter what your status, if you want some of what is being given away or sold, you must present yourself in person and in good time.

one must put forth an effort in order to succeed. This saying comes from physical fitness instructors. They say that if you do not exercise hard enough to make your muscles hurt, the exercise is not doing you much good.

Be careful of presumptuous people who take more initiative than they should. If you do someone a small favor or delegate a little permission or a little power, he or she may take advantage of you.

Do not bother trying to improve something if it is already working satisfactorily. That is a waste of time and you run the risk of breaking the thing while you are trying to improve it.

A person expects to be respected for making an effort even if it does not succeed.

While trying to solve one problem, we create an even bigger problem. We would have been better off if we had done nothing.

Do not instantly let your feelings control your actions. Slow down. Think before you react.

This refers to a plan that has gone wrong. When one is drinking from a cup, one intends to get all the drink into the mouth, but this does not always happen. The plan is good but it can still fail.

People will act according to their nature, including some mischief. This is sometimes used to describe irresponsible but not too seriously wrong behavior by men. In other words, grown men will sometimes act like little boys.

Do not associate with bad people. They may spoil you as a rotting apple spoils the apples next to it in the barrel.

People are generally not trustworthy. It is therefore better to deal with a familiar person or situation than an unknown one. That way you know what to watch out for and you can protect yourself better.

Everyone has shortcomings. This is used as an excuse for a minor Mistake that has been made.

People are never satisfied with what they have. They always want what someone else has.

The way a man dresses will affect the way he sees himself and the way other people see him. The implication is that if you want to succeed, dress for success.

Two people are more likely to succeed than one working or thinking alone. It is better to consult than to act alone.

One should admire a person, particularly a woman, for her deep, inner character and not simply for her superficial beauty.

Do not take large risks all by yourself. Do not walk alone on a dangerous street at night.

One should be kind to close relatives before doing good to the community in general.

Do not stay silent when you see a problem or an injustice. Speak out against it. Say, "Enough is enough." or people will think you do not mind the situation.

What you do to others, especially if it is bad, will eventually be done to you. As you seek your own success, do not treat other people badly. They may take revenge and spoil your success.

When one is tempted to cheat, this proverb serves as a reminder of the importance of good character. Honesty brings trust and trust leads to success.

If an accusation is true, accept the blame. This saying can also mean, " if a suitable opportunity comes to you, take it!"

Even when given an opportunity, some people will not use it. In that case the blame is all on him.

You created a certain situation so you are now responsible to take the consequences.

Since the pot and the kettle are equally black from the cooking fire, the pot has not right to criticize the kettle. This might be used if someone known to be a gossip criticizes someone else for gossiping.

When someone treats you badly, do not just get angry, express your anger in action.

Do not be so unreasonably critical about tiny things. Find something better to do with your time.

I am absolutely loyal to my country whether or not I agree with its policy in a certain area.

Never assume that all the blame for a conflict lies on one side, especially if you have heard only one side of the story.

Conflicts should be resolved and ended, not left alone to cause years of regret, bitterness and pain.

When you work, work. When you play, play. It is inefficient and therefore unwise to try to mix the two.

Do not meddle in something that will cause you no trouble if you leave it alone. If you wake up the "dog," it may bite you.

My true friend is the one who show loyalty to me by helping me when I am in need.

Do not attact anyone if you have no way to defend yourself when they attact you in the same way.

As positive and negative magnets attract each other, so people of very different types attract each other. For example, a quiet woman marries a very outgoing man. These differences have a mixed effect on the couple, partly making them interested in each other but also leading to miscommunication and conflict.

Punctuality is important. If you want to succeed, arrive early, like the bird that hunts worms at dawn before they go into hiding for the day.

Blood relationship is stronger than voluntarily chosen friendship. Brothers will stick up for each other against their own friends if they have to. This proverb is not quoted much anymore because kinship is not as highly valued as it used to be.

It is normal for humans to make mistakes and it is godly (or God-like) to forgive them.

Through acting quickly is generally a good thing, acting too quickly may cause troulbe. This proverb is used when someone has done a job carelessly and wrongly. For example, a carpenter in a hurry may cut a board too short and have to throw it away.

If you do not seize the opportunity, rain may come and spoil the hay before you get into the barn.

Withdraw from an activity if you don't like the conflict and criticism it brings. Let other people do it without you.

It's dished out in large and small pieces and when's gone, it's gone. If we ask for more than our share, we're just begging to be disappointed.

A conflict maybe resolved more deeply and effectively by writing the truth than by resorting to violence.

A new person in power will change many things and improve the situation. change is better than leaving things as they are.

No matter how bad things are right now, a person may hope for better prospects in the morning. New opportunities will come.

Opportunity is like an unexpected stranger passing by. It knocks on someone's door. If the person fails to answer the door, opportunity goes away and knocks on someone else's door. It does not return to the same person.

Do business with strangers as if they were brothers and with brothers as if they were strangers.

There are patterns in history. Nations rise and fall for similar reasons. Nations do not change their ways or learn from the mistakes of others. They repeat them.

A man without enemy is a man without quality. Think not? Even Jesus Christ had many, many enemies.

Though being on time is better than being late, doing something late is better than giving up or doing nothing.

People problems sometimes must be dealt with harshly. When you make an example of someone, make sure that everyone knows what the lesson is.

A son will be like his father. This may be quoted whenever the son has done something that reminds people of the father. Whether it is good or bad.

People will take advantage of a situation if they can. Employees will get lazy if the supervisor is not keeping an eye on them. A teenage son or daughter might hold a wild party at home during a weekend when the parents have gone out of town.

Do not criticise beyond necessity and seldom in public. And always precede criticism with a few words of praise.

If a person is taking advantage of someone else, the situation may change. The one on top may end up on the bottom. Then the one who has turned the tables will say, "I am only doing to you what you did to me.

Things may change quickly. This is said as a criticism of a person who changes quickly for no good reason. It may also be said of a thing or situation which does not last. Change is not good when it indicates unreliability.

1. struct的巨大作用
　　面對一個人的大型C/C++程序時，只看其對struct的使用情況我們就可以對其編寫者的編程經驗進行評估。因為一個大型的C/C++程序，勢必要涉及一些(甚至大量)進行數據組合的結構體，這些結構體可以將原本意義屬于一個整體的數據組合在一起。從某種程度上來說，會不會用struct，怎樣用struct是區別一個開發人員是否具備豐富開發經歷的標志。

　　在網絡協議、通信控制、嵌入式系統的C/C++編程中，我們經常要傳送的不是簡單的字節流（char型數組），而是多種數據組合起來的一個整體，其表現形式是一個結構體。

　　經驗不足的開發人員往往將所有需要傳送的內容依順序保存在char型數組中，通過指針偏移的方法傳送網絡報文等信息。這樣做編程復雜，易出錯，而且一旦控制方式及通信協議有所變化，程序就要進行非常細致的修改。

　　一個有經驗的開發者則靈活運用結構體，舉一個例子，假設網絡或控制協議中需要傳送三種報文，其格式分別為packetA、packetB、packetC：

struct structC
{
int a;
char b;
float c;
}
　　優秀的程序設計者這樣設計傳送的報文：

struct CommuPacket
{
int iPacketType;　　//報文類型標志
union　　　　　　//每次傳送的是三種報文中的一種，使用union
{
? struct structA packetA;
? struct structB packetB;
? struct structC packetC;
}
};
　　在進行報文傳送時，直接傳送struct CommuPacket一個整體。

// pSendData：發送字節流的首地址，iLen：要發送的長度
Send(char * pSendData, unsigned int? iLen);
發送方可以直接進行如下調用發送struct CommuPacket的一個實例sendCommuPacket：
Send( (char *)&sendCommuPacket , sizeof(CommuPacket) );
假設接收函數的原形如下：
// pRecvData：發送字節流的首地址，iLen：要接收的長度
//返回值：實際接收到的字節數
unsigned int Recv(char * pRecvData, unsigned int? iLen)；
　　接收方可以直接進行如下調用將接收到的數據保存在struct CommuPacket的一個實例recvCommuPacket中：

Recv( (char *)&recvCommuPacket , sizeof(CommuPacket) );
　　接著判斷報文類型進行相應處理：

switch(recvCommuPacket. iPacketType)
{
??? case PACKET_A:
??? …??? //A類報文處理
??? break;
??? case PACKET_B:
??? …　? //B類報文處理
??? break;
??? case PACKET_C:
??? …?? //C類報文處理
??? break;
}
　　以上程序中最值得注意的是

Send( (char *)&sendCommuPacket , sizeof(CommuPacket) );
Recv( (char *)&recvCommuPacket , sizeof(CommuPacket) );
　　中的強制類型轉換：(char *)&sendCommuPacket、(char *)&recvCommuPacket，先取地址，再轉化為char型指針，這樣就可以直接利用處理字節流的函數。

　　利用這種強制類型轉化，我們還可以方便程序的編寫，例如要對sendCommuPacket所處內存初始化為0，可以這樣調用標準庫函數memset()：

2. struct的成員對齊
　　Intel、微軟等公司曾經出過一道類似的面試題：
1. #include <iostream.h>
2. #pragma pack(8)
3. struct example1
4. {
5. short a;
6. long b;
7. };
8. struct example2
9. {
10. char c;
11. example1 struct1;
12. short e;???
13. };
14. #pragma pack()
15. int main(int argc, char* argv[])
16. {
17. example2 struct2;
18. cout << sizeof(example1) << endl;
19. cout << sizeof(example2) << endl;
20. cout << (unsigned int)(&struct2.struct1) - (unsigned int)(&struct2) << endl;
21. return 0;
22. }
　　問程序的輸入結果是什么？
　　答案是：
8
16
4
　　不明白？還是不明白？下面一一道來：
2.1 自然對界
　　struct是一種復合數據類型，其構成元素既可以是基本數據類型（如int、long、float等）的變量，也可以是一些復合數據類型（如array、struct、union等）的數據單元。對于結構體，編譯器會自動進行成員變量的對齊，以提高運算效率。缺省情況下，編譯器為結構體的每個成員按其自然對界（natural alignment）條件分配空間。各個成員按照它們被聲明的順序在內存中順序存儲，第一個成員的地址和整個結構的地址相同。
　　自然對界(natural alignment)即默認對齊方式，是指按結構體的成員中size最大的成員對齊。
　　例如：
struct naturalalign
{
char a;
short b;
char c;
};
　　在上述結構體中，size最大的是short，其長度為2字節，因而結構體中的char成員a、c都以2為單位對齊，sizeof(naturalalign)的結果等于6；
　　如果改為：
struct naturalalign
{
char a;
int b;
char c;
};
　　其結果顯然為12。

2.2指定對界
　　一般地，可以通過下面的方法來改變缺省的對界條件：
　　· 使用偽指令#pragma pack (n)，編譯器將按照n個字節對齊；
　　· 使用偽指令#pragma pack ()，取消自定義字節對齊方式。
　　注意：如果#pragma pack (n)中指定的n大于結構體中最大成員的size，則其不起作用，結構體仍然按照size最大的成員進行對界。
　　例如：
#pragma pack (n)
struct naturalalign
{
char a;
int b;
char c;
};
#pragma pack ()
　　當n為4、8、16時，其對齊方式均一樣，sizeof(naturalalign)的結果都等于12。而當n為2時，其發揮了作用，使得sizeof(naturalalign)的結果為8。
　　在VC++ 6.0編譯器中，我們可以指定其對界方式，其操作方式為依次選擇projetct > setting > C/C++菜單，在struct member alignment中指定你要的對界方式。
　　另外，通過__attribute((aligned (n)))也可以讓所作用的結構體成員對齊在n字節邊界上，但是它較少被使用，因而不作詳細講解。

2.3 面試題的解答
　　至此，我們可以對Intel、微軟的面試題進行全面的解答。
　　程序中第2行#pragma pack (8)雖然指定了對界為8，但是由于struct example1中的成員最大size為4（long變量size為4），故struct example1仍然按4字節對界，struct example1的size為8，即第18行的輸出結果；
　　struct example2中包含了struct example1，其本身包含的簡單數據成員的最大size為2（short變量e），但是因為其包含了struct example1，而struct example1中的最大成員size為4，struct example2也應以4對界，#pragma pack (8)中指定的對界對struct example2也不起作用，故19行的輸出結果為16；
　　由于struct example2中的成員以4為單位對界，故其char變量c后應補充3個空，其后才是成員struct1的內存空間，20行的輸出結果為4。

[轉]WTL之父Nenad Stefanovic訪談錄

???作為現代C++最重要的特色技術，template正在各個傳統領域攻城略地。從基本算法與數據結構，到正則表達式與XML解析，從高性能數學計算，到資源的分配與管理，從網絡分布式計算環境，到組件模型創建，從靜態多態性的維度擴展，到設計模式的自動生成，神奇的template顯示出其令人嘆為觀止的強勁實力，如果不是有一個隱隱的痛處，template愛好者簡直可以去狂歡了。

這個隱隱的痛處，就是在GUI編程領域。

???現有的大部分成熟GUI框架和工具庫，其定型時間都在90年代早期，不管是因為什么原因，總之我們根本看不到template技術在這些環境中的任何重要運用。無論是專有MFC和OWL，還是開源的wxWindow和Mozilla, 以至于是專有還是開源都說不清楚的Qt，它們在其他方面有著諸多不同，偏偏倒是在對待模板技術上空前一致：嚴格限制在底層的數據結構領域內，抵制模板技術流入GUI主體結構。最過分的wxWindow和Mozilla，在代碼編寫規范里嚴厲禁止使用1990年之后發展出來的任何C++特性，模板、異常、多繼承、STL等等，均在黑名單上。諸位有興趣，不妨去看看，那與其說是一份C++代碼編寫規范，倒不如說是對C++現代特性在GUI領域應用的一份不公正的判決書。

難道模板技術真的在GUI領域無用武之地嗎？

WTL給出了一個響亮的回答。

???WTL是微軟ATL開發組成員Nenad Stefanovic先生在ATL Windowing機制上發展起來的一整套GUI框架，運用template技術組織和創建GUI對象，構筑了精致的面向對象框架（沒錯，在這里object oriented與template達成了精致的融合）。雖然沒有獲得微軟的官方支持，雖然其使用者人數很少，但是確實是“用過的都說好”，有位微軟MVP人士甚至說，這是微軟有史以來推出的最優秀的一個framework。真是一個有趣的諷刺，最好的東西居然不被官方支持。有關于WTL的流言不少，比如這東西原本是微軟內部專用，只是因為不小心才被泄漏出來等等，這更加劇它的神秘色彩。相信大家對它一定有不少問題。我們特別邀請到了WTL之父Nenad Stefanovic先生，進行了一次網上的訪談，希望能幫助大家了解WTL的真面目。

【C++ View】：I think most of our readers are not very familiar with you, so would you please tell us your story here? We are very fond of that. What do you think about China and Chinese people?

【C++ View】：我想，可能我們的讀者中有很多人對您還不是很熟悉，您能不能在此給我們簡單介紹一下您自己呢？我們將非常樂意聽到您的自述。還有，您能不能也對我們講述一下您對于中國以及中國人民的基本看法呢？

【Nenad】: I am a software developer at Microsoft. Your readers will probably know me as a creator of Windows Template Library, WTL. I am from former Yugoslavia, where I finished school and started working on software development. I've been living in US for 10 years now.

I am intrigued and impressed by the Chinese culture and tradition. I think that China is now in a great position of progress as a country and a nation. I discovered that, being from former Yugoslavia, I already know many things about China, and getting to know people from China gave me a bit of the "everyday" life perspective as well. I'd like to learn more, so I hope to visit China one day.

【Nenad】：好的。我現在在Microsoft工作，是它里面的一個軟件開發人員。你們雜志的讀者中可能有人知道，我就是Windows Template Library （WTL）的創作者。我來自于前南斯拉夫，在那我完成了我的學業并開始了我作為軟件開發人員的工作生涯。現在，我在美國居住的時間已經超過了10年了。

???中國的文化以及傳統給我留下了極為深刻的印象，我對此十分感興趣。我想，作為一個國家以及民族，中國已經處于一個偉大并且不斷在成長中的位置上。作為一個從前南斯拉夫來的人，我早就了解到關于中國的很多事情。在與來自中國的人民的接觸過程中，我還了解到了你們日常生活的一些狀況。我還想了解更多（有關中國的事情），希望有一天我可以到中國來游覽。

【C++ View】：When and why did you first think about WTL? What's its original purpose? How do you see its future?

【C++ View】：您是什么時候開始想起要開發WTL呢？為什么？您在開發它時的最初目的是什么？您又是如何地看待它未來的發展呢？

【Nenad】：WTL was born while I was working on ATL (Active Template Library). We were extending ATL to support ActiveX controls, and I was working on the windowing support. I started thinking that the same techniques can be applied to much broader windowing support, for the much richer UI for controls, components, and also applications. So, WTL was created as a part of ATL that would extend ATL to support any kind of UI related component or application. It did not ship with ATL in Visual Studio, however, so I decided to ship it as a standalone library that extends ATL.

I think that WTL will continue to be a great option for developers writing Windows applications and components. I don't see big changes or additions to WTL, because one of the design principles for WTL was to follow the Win32 UI API and design. It will continue to do so.

【Nenad】：WTL是我在從事ATL （Active Template Library）開發工作時的產物。那時我們正在擴展ATL，使之得以支持ActiveX control，而我負責的就是其中對于窗口機制部分的支持。這時，我就開始想，是不是可以把同樣的技術應用到更為廣泛的窗口機制中，以獲得更豐富的UI控制、組件、以至于應用程序呢？于是，作為ATL的一部分，WTL被開發出來了。它將ATL進行了擴展，以使得它可以支持各種類型的與UI相關的組件或者應用程序。然而，它并沒有隨著ATL一同集成在Visual Studio中被發布，于是我就決定將它作為一個單獨的ATL擴展庫發布出去。

我認為WTL將一直是那些在Windows下開發應用程序以及組件的開發者的一個很好的選擇。我并不認為在以后，我們會對WTL有一個大的改動（或者增添），因為WTL的一個設計宗旨就是“遵循Win32 UI的API及其設計”。現在如此，將來還是會如此下去。

【C++ View】：I first heard about WTL in July, 2000. At that time, I thought: "No official support, no documentation, no commercial hype, it will die in 6 months." Now, fifteen months passed, it spreads wider and be more vigorous. Lots of C++ programmers, esp. the ones we regard them as "gurus and masters" involved in WTL. I know it's surely because WTL is a wonderful library, but it must be more than a wonderful library to gain such attentions without official force.What do you think WTL's relative success? What's the reason?

【C++ View】：我第一次接觸WTL是在2000年7月。在那時，我就想：“沒有官方的支持，沒有文檔，也沒有商業吹捧，它最多只能夠存活6個月。”但現在15個月過去了，它反而流傳得更為廣泛，更加的生機勃勃。許多C++程序員，尤其是一些我們所認知的“專家”以及“大師”，都在使用WTL。我當然知道這主要是因為WTL的出色，但我想，能夠在沒有官方的力量牽涉的情況下吸引如此多的注意，WTL一定還有更出色的東西，請問您是如何看待WTL的成功呢？它成功的原因又是什么？

【Nenad】： I think that the main reason of WTL's success is that it did fit the need of developers at the right time. More and more developers started using ATL, and it was natural for them to start using WTL when they needed more UI support. It seems that WTL was perceived as a more open project than others, judging by the support provided by other parties in the development community. Many people did a wonderful job of creating samples, documentation and support for WTL. The support from the programming community is very important part of the acceptance and success of WTL.

【Nenad】：我認為WTL成功的最主要原因就是，它確實而且及時地滿足了開發者的需求。越來越多的開發人員開始使用ATL，當他們需要更多的UI支持時，他們很自然的就會開始使用WTL。從其他的開發團隊所提供支持來看，WTL看起來似乎要比其他的項目更加開放。許許多多人為WTL做了大量工作，如：創建示例代碼，撰寫文檔等。WTL之所以能夠被廣為接受并獲得如此大的成功，來自于這些開發團隊的支持絕對是一個重要的因素。

【C++ View】：What do you think about MFC? Do you like it? If you don't, why? And the most confusing thing is Managed C++, is it C++? Do the leaders of MC++ really think some C++ users will go to learn it? Do you believe?

【C++ View】：請問您對于MFC是怎么看的？您喜歡它嗎？如果不，為什么呢？還有，最讓人迷惑不解的就是Managed C++了，它是不是C++呢？MC++的提倡者是不是真的認為會有一些C++的用戶轉而去學習它呢？您的看法又是如何呢？

【Nenad】： I think that MFC is a great framework library. Don't forget that MFC was designed at the time that C++ compiler was rather limited, and the main platform was 16-bit Windows. Unfortunately, because MFC was designed as a framework, it was really hard to evolve it to use better C++ support in newer compilers, and to add support for new features added to Windows in the meantime. What I don't like about MFC is the DLL approach, which causes many compatibility problems, and framework design, which dictates too many things about app design.

Managed C++ is an extension to C++ which allows C++ programs to use managed code. It is very important to understand that you can compile your existing C++ code using MC++ without any changes. MC++ allows developers to use both familiar non-managed C++ and managed code in the same module. That provides an excellent way to extend existing code to interact with managed code, as well to create new projects that can use both managed and traditional C++.

【Nenad】：我認為MFC是一個了不起的框架庫。請不要忘了，在MFC被設計出來初期，那時的C++編譯器還具有很多的限制，并且那時主要的平臺還只是16位的Windows。不幸的是，由于MFC被設計成為一個框架，使得我們很難利用新編譯器中那些更好的C++特性來改進它，也很難將Windows中的很多新特性添加到MFC中。我不喜歡MFC的地方是它高度依賴DLL的特性——因為它將導致許多兼容性方面的問題；還有就是MFC的整個框架設計——它在應用程序的設計中限定了太多東西。

Managed C++是C++的一個擴展，它允許C++程序得以使用受管（managed）代碼。我們需要了解的一個很重要的特性就是，我們可以使用MC++來編譯已有的C++代碼而無需對它們進行任何改動。MC++允許開發者同時使用他們所熟悉的非受管代碼以及受管代碼來開發同一個模塊。這就提供了一個非常好的途徑，使已有的代碼與新的受管代碼相互作用，并也可使得我們創建一個項目，同時使用受管的和傳統的C++代碼。

【C++ View】：In the past 15 years or more, C and C++ is the base of almost all Microsoft's technologies(OS, COM, etc.). We C++ user paid a lot of hard work to catch them, because we felt what we paid was worthy(?). Now, it seems the climate changed. .NET is coming, the world is going to be full of CLRs and/or JVMs. There has been a decampment from C++. So what do you think about the future of C++ (not MC++) in Mircosoft technologies? Will it go away? Will it become a marginal language?

【C++ View】：在過去的15年中（甚至更長的一段時間內），C以及C++構成了幾乎所有Microsoft技術的基礎（如：OS，COM等）。我們這些C++用戶花費了大量的時間來熟悉并掌握它們（C以及C++），因為我們相信我們所付出的一定會有回報（?）。但現在的風向好像有了很大的改變。.NET出現了，世界似乎就要充斥CLR （Common Language Runtime，公共語言運行庫）以及／或JVM （Java Virtual Machine，Java虛擬機）。現在C++已經出現了退潮的跡象。那么，請問您對于C++（不是MC++）在Microsoft技術中的前景如何看待？它是否會由此消亡？還是就此淪落為一門邊緣語言？

【Nenad】：Well, the world is changing too. The new type of development for Web services and connected applications is on the horizon. I think that new languages, like Java, C#, and VB.NET, were developed to address two main issues - to simplify software development and to provide better support for Internet development. Simplifying software development allows more developers to write good applications and cuts down on time needed to finish a project. Supporting Internet development is obviously very important in this time when Internet is used more and more in every part of everyday life.

I think that C++ will continue to be an important language, especially for ISV's and for system development. On the other hand, I believe that .NET will be very important platform soon. .NET has the potential to be the main programming platform for the future, but it is reasonable to expect that the transition will take some time.

【Nenad】：是的，世界也已經發生了變化。對于網絡服務以及連接這樣的新型應用程序的開發已經浮上了水面。我認為那些新的編程語言（如Java，C#，以及VB.NET）都是針對以下兩個主要的問題而開發出來的——簡化軟件的開發過程以及對于Internet應用程序開發提供更好的的支持。簡化軟件的開發過程使得更多的開發者可以寫出更多更好的應用程序并減少完成開發項目所需要的時間。而支持Internet的開發，對于這個Internet越來越深入到我們的日常生活中的時代來說，毫無疑問是一件非常重要的事情。

我認為C++會繼續作為一門重要的編程語言發揮作用，尤其是對那些獨立軟件開發商和那些系統級開發來說更是如此。從另一方面來說，我相信.NET將會在不久以后成為另外一個非常重要的開發平臺。對于未來來說，.NET擁有成為主流編程平臺的潛力，但我們必須認識到，這樣的過渡階段肯定要持續一段時間。

【C++ View】：There a lots of beginners in our readers, after they learn (standard) C++, they want to seek a path to master enought Microsoft technologies to be practical and proficient programmers. Could you recommend such a path? Should they learn Win32 API programming? Is it worthy of studying MFC? Is WTL/ATL/STL a reliable solution? Or goto C# directly? Many many people will thank you if you give them frank advice.

【C++ View】：我們的讀者中有很多是初學者，在他們學習完（標準）C++后，他們希望能夠找到一條道路，掌握到足夠多的Microsoft的技術使自己成為經驗豐富的、熟練的程序員。您能不能給我們指出這樣的一條道路來呢？我們是不是應該學習Win32 API編程？學習MFC是否是值得的？WTL/ATL/STL算得上是一個可靠的解決方案嗎？又或是我們應該直接學習C#？如果您能夠給我們一些建議，相信會有很多的人為此而感激您的。

【Nenad】：I think that depends on their plans and ambitions. The more of those things you do, the better you are off in the long run. But, you also have to balance that with the practical issues. So, I think that people who see their future in the Internet development can go directly to C# or VB.NET, and study .NET platform. Those who would like to have more knowledge of the Windows platform and services it provides should certainly learn more about Win32 API and libraries that support Windows programming.

【Nenad】：我認為這主要取決于他們的計劃以及雄心。你所做的越多，在長時間競爭中你就越占據優勢。不過你也要注意保持與實際問題的平衡。我建議那些決心以后只做Internet相關開發的人可以直接去學習C#或者VB.NET，同時學習.NET平臺。而那些更多地了解Windows平臺以及它所提供的服務方面知識的人，當然就必須需要更多地了解有關Win32 API以及那些支持Windows編程的庫相關的知識。

【C++ View】：Soon after I began to learn WTL, a warm-hearted man posted me a email. He wrote: "You won't be a good WTL programmer if not a good ATL programmer, you won't be a good ATL programmer if not a COM programmer. And once you decide to learn COM, you are beginning your travel to hell." Is COM so difficult to learn? How to study WTL? We must learn API, COM, ATL and WTL in sequence, do we? And what about COM, will it remain to be the core technology of Microsoft, or just be substituted by .NET and dismiss?

【C++ View】：在我剛開始學習WTL后不久，有一位熱心人給我發了份郵件。他寫道：“如果你不是一個好的ATL程序員的話，你就不可能成為一個好的WTL程序員；如果你不會COM編程的話，你就不可能成為一個好的ATL程序員；但一旦你決定開始學習COM，你就邁出了踏向地獄的第一步。”COM是不是真的那么難學？我們應該如何地來學習WTL呢？我們是不是應該按照這樣的順序學下來呢，API->COM->ATL->WTL？還有，COM將會變得如何？他是不是還能夠保持Microsoft的核心技術這一頭銜，抑或是被.NET給替換掉然后就此消失？

【Nenad】：I don't think it is necessary to master COM to use and understand WTL. Win32 UI knowledge is more important than COM to understand WTL. But it is true that knowledge of ATL is required, and ATL mainly supports COM. So, COM knowledge is desirable, but not required.

I don't think that COM is hell, but it sure does require a lot to learn to be an expert. Keep in mind that many people don't have to be COM experts to use COM, or to use WTL. Just understanding basic principles of COM is enough to use it, and then people can learn more when needed.

【Nenad】：我不認為使用和理解WTL就一定要掌握COM。相比于COM來說，Win32 UI的知識對于理解WTL顯得更為重要。但毫無疑問的是，ATL的相關知識是必不可少的。由于ATL主要任務就是支持COM，所以，有COM的知識只是會更好一些而已，但它們并不是必需的。

我也不認為COM是一個噩夢，但毫無疑問的是，想要成為一個COM專家，要學的東西實在是太多了。但請記住一件事情，很多使用COM或者WTL的人并不都是COM方面的專家。要想使用它們，人們所需了解的只是一些COM的基本原理就夠了，其他的相關的知識則可以在需要時再去學習。

【C++ View】：What do you think about Generic Programming? Is it a whole different paradigm from OOP, or just OOP's supplemental facility? Can we combine GP and OOP? In the hard work of design and implement WTL, you must had got an insight about the relationship between OOP and GP, what's it?

【C++ View】：請問您對于泛型程序設計是如何看待的？它到底是OOP的一個補充呢，還是完全不同于OOP的另外一個程序設計范型呢？我們是否可以將GP以及OOP一同聯合使用？我想，在設計和實作出WTL的艱苦過程中，對于OOP以及GP之間的關系，您一定有了自己的看法，您能不能給我們說一下呢？

【Nenad】：Generic Programming and OOP are very different, mostly because Generic Programming doesn't explicitly express relationships between design elements. They can, however, be used together very efficiently.

WTL uses a combination of Generic Programming and OOP design. Templates are mostly used to implement traditional OOP classes. I'd like to point out that WTL doesn't use any "pure" design, and it doesn't strictly follow any design guidelines or styles. I do think, though, that WTL does use one of the main strengths of the C++ language - it uses appropriate paradigm that is the most suitable for a particular problem.

【Nenad】：GP和OOP非常不同，這主要是由于GP從不顯式地表達出設計元素之間的關聯來。然而，它們也可以被非常高效地組合運用。

WTL中使用了一種GP連同OOP的設計。我在其中大量使用了模板來實作出傳統的OOP中的類。我很樂意指出的是，WTL中并沒有使用一種“純”設計，它也沒有遵循任何的設計指導方針或者設計規格。可是，我還是認為WTL使用到了C++語言中的最主要的精髓處——對于一個特定的問題使用一種最適合它的適當典范。

【C++ View】：Recently, the famous C++ pioneer Stanley Lippman joined Microsoft and became a member of Visual C++.NET group. How do you think about this? What message do you think your company like to pass to public? Does this mean Microsoft want to make VC.NET a full-standardized C++ compiler and hold C++ as your core system language?

【C++ View】：最近，著名的C++元老級大師Stanley Lippman加入了Microsoft并成為其VC.NET開發小組中的一員。請問您對于此事是如何看待的？您認為Microsoft試圖向公眾傳播一種什么樣的信息呢？這是否也意味著Microsoft希望VC.NET成為一個完全標準化的C++編譯器，并繼續保持C++的核心系統語言地位呢？

【Nenad】：I think that shows that Microsoft is committed to advance the C++ compiler and language, and ready to get the best people to help. I am sure that VC++.NET will continue to be powerful tool for developing applications, and that it will also include additional capabilities for the .NET development. Compliance with the C++ Standard is an ongoing work, and we will see further improvements there, too.

【Nenad】：我認為這顯示了Microsoft對于促進C++編譯器以及語言繼續發展的決心，并為此找到了最佳人選來獲取幫助。我確信VC.NET將會繼續是開發應用程序的強有力工具，并且它同時還將包含有.NET開發能力。目前我們正在進行兼容C++標準方面的工作，不久我們就會看到成效。

【C++ View】：I'm learning WTL and ATL, since you are the author of WTL and a member of ATL group, can you give me some advice?

【C++ View】：我現在正在學習WTL以及ATL，既然您是WTL的作者，同時又是ATL開發小組中的一員，您能不能給我一些建議呢？

【Nenad】：There are several areas of programming that are very important for WTL and ATL: knowledge of the C++ language in general, understanding of templates, COM for ATL, and Windows UI programming for WTL. Solid knowledge in these areas is very beneficial for WTL and ATL developers, and it also helps to understand the source code for both libraries.

I would also like to encourage everybody to write programs. That is the best way to learn how to use any library, or a programming language or operating system. Writing programs often brings problems that must be solved that are not addressed in books. Reading about something is very useful to start learning, writing programs is the best next step.

【Nenad】：對于WTL和ATL來說，有好幾個編程方面的領域是十分重要的：大體上的C++語言知識，了解模板，COM（對ATL而言），以及Windows UI編程（對WTL而言）。在這些領域有著堅實的基礎對于WTL以及ATL開發人員來說有著很大的好處，同時對于理解這兩個的源代碼也能夠起到幫助作用。

我同樣也很樂意去鼓勵大家多寫程序。這也是學習如何使用一個程序庫，或者一門編程語言，或者一個操作系統的一個最好的方法。在寫程序的過程中經常會出現一些書本上沒有提及但又必須被解決的問題。在開始學習時讀一些東西是很有用的，而寫程序則是向縱深發展的最佳方式。

【C++ View】：They say we are in the gate of Post-PC times, it will be a embedded world, and there will be embedded smart device everywhere, and the embedded industry will build a far large market compare to PC's. Do you believe it? Do you think WTL and other C++ template libraries are available and appropriate for embedded development? Are there available for Internet development?

【C++ View】：有人說，我們現在已經處于后PC時代的門口，未來將會是一個嵌入系統的世界，嵌入式的智能設備將會無所不在，并且對比PC來說，嵌入系統的產業將會是一個更大的市場。您是否相信這些呢？您是否認為WTL以及其他的一些C++模板庫對于嵌入式開發也適用呢？它們是否適合Internet開發？

【Nenad】：Yes, I think that large number of various devices that we use everyday will become small, specialized computers. That doesn't mean that the number and importance of PCs will go down, just that there are many other devices that will be enhanced to be programmable and connected. Those new devices will provide a great opportunity for software developers, because they will all have software and somebody has to write it.

Many of the C++ libraries are quite appropriate for embedded development, and WTL would also be in cases where Windows based user interface is important (for example, Pocket PC platform). Great flexibility and small footprint are always very important features for embedded development, so template libraries are in the very good position there.

【Nenad】：是的，我認為我們現今所使用的各種設備中的大部分在以后都將會演變成為一些小的，具有專門用途的計算機。但這并不意味著PC的數目以及重要性將會由此降低，只不過是表明還有著許多其他的設備需要被加強以使得我們可以對其進行編程并且連接。由于必須需要有軟件的支持，而軟件又需要有人來寫，這些新的設備將會給軟件開發人員帶來極大的機遇。

有許多的C++函數庫都可用于嵌入系統的開發，WTL也將會在那些Windows用戶界面較為重要的開發中（例如，在Pocket PC平臺上面開發）占有一席之地。對于嵌入式開發來說，良好的彈性，微小的內存耗用永遠都會是很重要的特性，而模板庫在這方面占據了一個非常好的地位。

【C++ View】：In the past 7 years or more, COM is Microsoft's core technology. And we now can see that in the next decade, the core role may be .NET. My question is, what's wrong with COM? Where will COM be? Will it disappear? Will it be substituted by something else? What's the relationship between COM and .NET? Is .NET based on COM? Is it worthy of learning COM now?

【C++ View】：在過去的7年（甚至更長的一段時間）內，COM都是Microsoft中的核心技術。現在我們可以預見到，在下一個十年間，這個核心將會變為.NET。我的問題就是，COM有什么過錯？COM將何去何從？它是否會逐漸消失呢，還是會被其他的一些技術給替代？COM和.NET之間的關系是什么樣的情況？.NET是否是基于COM之上呢？現在學習COM是不是還值得？

【Nenad】：Maybe you shouldn't ask what is wrong with COM, but just think of .NET as the evolution of COM. .NET extends what was started with COM- creating reusable binary components - and brings additional important features: rich metadata, great run-time, built-in security, versioning, etc. All of these new features are important for development today, and it is really great that .NET has extensive support for them. Interoperability between .NET and COM is also provided, so that the previously developed COM components can still be used in the .NET environment.

I still think that it is a good idea to learn COM - it is a great first step even for people who want to learn .NET, and it also provides better understanding of the design and implementation of .NET itself.

【Nenad】：或許你不應該問COM有什么過錯，而是應該把.NET看成COM的進化。.NET擴展了COM最初的目的——創建可重用的二進制程序組件——并向其中添加了很多重要的特性：豐富的元數據，了不起的運行庫，內建的安全機制，版本機制等。對于現今的軟件開發來說，所有的這些新的特性都非常重要，所以.NET能夠廣泛地支持它們，是一件很偉大的產品。Microsoft同時也提供了在.NET和COM之間進行互操作的能力，這使得以前所開發出來的COM組件在.NET環境中同樣也能夠得到使用。

我仍然認為學習COM是一個很好的主意——它甚至對于那些希望學習.NET的人們來說也是一個很好的開端，學習COM同時也有助于我們更深入地理解 .NET本身的設計和實現。

【C++ View】：I know you must be a C++ fan. Now the language is facing lots of challenges. To counterattack, Dr. Stroustrup suggest to develop many useful libraries, and teach the programmers to use C++ as a high level language. Now there are several wonderful modern C++ libraries. Aside of ATL, WTL and STL, there are still Boost library, MTL, ACE/TAO, DTL, etc. It seems the C++ community is preparing a movement. Do you think the movement will success? Why? What are your colleagues'(in Microsoft VC.NET group) attitude towards such a movement?

【C++ View】：我猜想您肯定是一個C++愛好者。現在這門語言面對著許多的挑戰。作為反擊措施，Stroustrup博士提議開發許多有用的庫，并引導C++程序員把C++當作一門高級語言來使用。現在我們已經可以得到好幾個極好的現代的C++庫，除去ATL、WTL以及STL之外，還有Boost庫、MTL、ACE/TAO、DTL等。一切都顯示著C++社區正在醞釀著一次變革。請問您覺得這場變革能否成功？為什么？您的那些Microsoft中的VC.NET開發小組中的同事對于此態度是怎樣的？

【Nenad】：C++ is a great language and its importance remains high, even with the new challenges. Libraries are an excellent addition to the language itself, as they provide very useful reusable code for developers. The existence of many great C++ libraries shows the size and strength of the C++ community. I think that is already a success, and that it will continue. You can be sure that the VC++.NET group is aware of the existing libraries, and I expect them to continue to enhance the support for them.

【Nenad】：C++是一門偉大的語言，即便遇到了新的挑戰，它仍然將是非常重要的。程序庫對于語言本身是極好的補充，它們為開發者提供了一些十分有用的可重用代碼。存在如此眾多的、了不起C++程序庫，這件事情本身就表明了C++社區的龐大和強大。我認為這場變革已經成功了，并且會一直成功下去。你們可以放心，VC.NET開發組是不會對這些已有的程序庫熟視無睹的，我預期他們會不斷地加強對于這些庫的支持。

【C++ View】：The last question. Since lots of people don’t acquaint themselves with WTL, now we have a chance for you, the father of WTL, to introduce WTL in a short speech here. What would you like to speak?

【C++ View】：最后一個問題。既然許多人并不了解WTL，作為WTL之父，您現在有機會在這里做一個演講，請簡短地介紹一下WTL。

【Nenad】：WTL is a template based library for user interface development. It extends ATL to provide classes for implementing user interface for applications, components, and controls. It provides classes for various user interface elements: top-level windows, MDI, standard and common controls, common dialogs, property sheets and pages, GDI objects, UI updating, scrollable windows, splitter windows, command bars, etc.

WTL is implemented using the same template architecture as ATL, so it is a natural fit for ATL developers. It also doesn't alter or hide Windows specific constructs, thus allowing Windows programmers to use WTL without surprises. The important design goal of WTL was to avoid inter-dependencies - classes themselves do not reference other WTL classes. That means that your program will contain just the code that you actually use, and nothing else. Coupled with the use of templates, this allows creation of very small programs without run-time dependencies.

WTL delivers the object oriented way to program for the Windows user interface, while keeping the code size small. It also provides a great foundation that developers can extend with their own classes.

And finally - WTL was written with a hope that developers will enjoy using it. I hope you will use it and enjoy it, too.

WTL是一個基于模板的、專為開發用戶界面的程序庫。它擴展了ATL，并提供了一些類用來實現應用程序的用戶界面、組件和控件。它提供了各種類來支持各種各樣的用戶界面元素：頂級窗口、MDI、標準控件和通用控件、通用的對話框、屬性表以及屬性頁、GDI對象、UI更新、可卷動的窗口、分割窗口、命令條等等……

WTL的實現使用了和ATL一樣的模板架構，所以對于ATL開發者顯得很自然。同時它并沒有改變或者是隱藏那些Windows相關結構，那些Windows程序員在使用WTL時也不會感到很吃驚。WTL的一個主要設計原則就是避免在沒有引用到其他WTL類時，出現不必要的內部依賴。這意味著我們的程序將只包含有我們實際上所使用的代碼，除此之外再無其他的東西。加上了模板的使用后，這樣做得到的結果就是一些非常小的，不依賴于運行庫的程序。

WTL專注于用面向對象的方法來編寫Windows的用戶界面程序，同時保持代碼的尺寸很小。同時，它也為開發者提供了一個很好的基礎，可以寫新的類來擴展WTL。

最后，我在編寫WTL時就希望開發者能夠喜歡在開發中使用它。我同樣也希望您能夠使用它并喜歡上它。

This type of conversion is called an "upcast" because it moves a pointer up a class hierarchy, from a derived class to a class it is derived from. An upcast is an implicit conversion.

If type-id is void*, a run-time check is made to determine the actual type of expression. The result is a pointer to the complete object pointed to by expression. For example:

If type-id is not void*, a run-time check is made to see if the object pointed to by expression can be converted to the type pointed to by type-id.

If the type of expression is a base class of the type of type-id, a run-time check is made to see if expression actually points to a complete object of the type of type-id. If this is true, the result is a pointer to a complete object of the type of type-id. For example:

This type of conversion is called a "downcast" because it moves a pointer down a class hierarchy, from a given class to a class derived from it.
小結：
? a???? 實際指向對象和?? b 目標對象,? b 是a 的基類（子對象），或者是2者同級轉換才成功
否則目標為NULL;也就是說不能向下轉

2?? 多重非虛的繼承模式

A pointer to an object of type D can be safely cast to B or C. However, if D is cast to point to an A object, which instance of A would result? This would result in an ambiguous casting error. To get around this problem, you can perform two unambiguous casts. For example:

Further ambiguities can be introduced when you use virtual base classes. Consider the class hierarchy shown in the following figure.

????//pd 指向 e 對象
void f(D* pd)
{
?? E* pe = dynamic_cast<E*>(pd);
?? B* pb = pe;????? // upcast, implicit conversion
?? A* pa = pb;????? // upcast, implicit conversion
}

//pd 指向 e 對象
void f(D* pd)
{
?? B* pb = dynamic_cast<B*>(pd);????? // cross cast
?? A* pa = pb;????????????????? // upcast, implicit conversion
}

? 也就是? 所謂 cross cast

二? typeid( type-id )???? typeid( expression )?
?? 此操作符返回個? const type_info &?
??????????? expression?必須指向一個多態類型（帶虛函數??? ），并且要解引用

#include <iostream>
#include <typeinfo.h>

/********************************************\
|????歡迎轉載, 但請保留作者姓名和原文鏈接, 祝您進步并共勉!???? |
\********************************************/

c語言中的類型轉換與復合類型

作者: Jerry Cat
時間: 2006/07/01
鏈接: http://www.shnenglu.com/jerysun0818/archive/2006/07/01/9274.html

數據類型轉換是C語言中頗具爭議的一個話題，這里不多加評論，單就其中整形與浮點型之間的轉換做一些解說.?
由于表示范圍的原因，你可能認為把整型數轉換為浮點型一定是安全的，但實際上不是這么簡單。因為浮點型存儲的數值雖然大但卻受精度的限制。
如unsigned int u=4294967295;
float f=u;
接過f變成了4294967296.000000
所以要把一個整形換成float在轉換回來還要和原先的數相同，則這個數只能有6位有效數字。否則會有精度損失。而要把浮點換成整形，首先可以肯定小數部分被舍掉了。另外還要注意，轉換的第一步必須是以下的一種類型：
int???? unsigned???? long???? unsigned long???? long long???? unsigned long long??
如：
float f=12345.678;
int i=f;
short s=i;
否則直接轉換到short 得到的就根本不是12345了。（與平臺有關，windows不存在這個問題）

對于復合類型，主要是要注意由于數據對齊要求而導致的存儲空間浪費。這里舉一個例子：
struct s
{
??? char x;
??? int y;
??? char z;
??? int u;
};???????????? /*s占16個字節*/
struct s
{
??? int y;??? /*4*/
??? int u;??? /*4*/
??? char x;??? /*1*/
??? char z;??? /*3*/
};???????????? /*s占12個字節*/
注意這里第二個定義中為什么不是10，這還是由于數據對齊的原因，因為不能只考慮單個變量的情況，還有可能是結構體數組變量，struct?s array[10]，知道原因了吧。另外一種可能就是在函數調用中，結構體變量作為一個參數要壓棧，是以4字節為一個單元壓棧的。

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