class Point
{
int x,y;
};
Point p;int x = 0; //瀵筰nt榪涜鍒濆鍖栵紱const char *text = " A C-style string"; //瀵規(guī)寚閽堣繘琛屽垵濮嬪寲錛?/span>double d;std::cin >> d; //閲囩敤input stream鐨勬柟寮忓畬鎴愬垵濮嬪寲錛?/span>class PhoneNumber{};class ABEntry{ //Address Book Entry;public:ABEntry(const std::string &name, const std::string &address, const std::list<PhoneNumber> &phones);private:std::string theName;std::string tehAddress;std::list<PhoneNumber> thePhones;int numTimesConsulted;};ABEntry::ABEntry(const std::string &name, const std::string &address, std::list<PhoneNumber> &phones){//浠ヤ笅鍏ㄦ槸璧嬪?assignment)錛屼笉鏄垵濮嬪寲(initialization);theName = name;theAddress = address;thePhones = phones;numTimesConsulted = 0;}ABEntry::ABEntry(const std::string &name, const std::string &address,const std::list<PhoneNumber> &phones)
: theName(name),
theAddress(address),
thePhones(phones),
numTimesConsulted(0)
{}//鏋勯犲嚱鏁版湰浣撲笉闇瑕佷換浣曞姩浣?/span>ABEntry::ABEntry():theName(), //璋冪敤theName鐨勬瀯閫犲嚱鏁?/span>theAddress(), //璋冪敤theAddress鐨勬瀯閫犲嚱鏁?/span>thePhones(), //璋冪敤thePhomes鐨勬瀯閫犲嚱鏁?/span>numTimesConsulted(0) //璁板緱灝嗘鍐呯疆綾誨瀷鏄懼紡瀹氫箟涓?{}class FileSystem{public:std::size_t numDisks() const;};extern FileSystem tfs;//棰勫緇欏鎴蜂嬌鐢ㄧ殑瀵硅薄錛宼fs浠ｈ〃"the file system"鐜板湪鍋囪寤虹珛浜嗕竴涓猚lass鐢ㄤ互澶勭悊鏂囦歡緋葷粺鍐呴儴鐨勭洰褰曘傚緢鑷劧錛屼粬浠細(xì)鐢ㄤ笂theFileSystem鐨勫璞★細(xì)
class Directory{public:Directory();};Directory::Directory(){std::size_t disks = tfs.numDisks();}Directory tempDir(params);//涓轟復(fù)鏃舵枃浠惰屽仛鍑虹殑鐩綍
鐜板湪錛屽垵濮嬪寲鐨勯噸瑕佷綔鐢ㄦ樉紺哄嚭鏉ヤ簡錛岄櫎闈瀟fs鍦╰empDir涔嬪墠琚垵濮嬪寲錛屽惁鍒檛empDir鐨勬瀯閫犲嚱鏁頒細(xì)鐢ㄥ埌灝氭湭鍒濆鍖栫殑tfs銆備絾鏄痶fs鍜宼empDir鏄笉鍚岀殑浜哄湪涓嶅悓鐨勬椂闂村垱寤哄嚭鏉ョ殑錛屼粬浠槸瀹氫箟浜庝笉鍚岀紪璇戝崟鍏冨唴鍦皀on-local static瀵硅薄錛屽浣曡兘紜tfs鍦╰empDir涔嬪墠鍏堣鍒濆鍖栵紵
鍝︼紝榪欐槸鏃犳硶紜鐨勩?br>涓涓皬灝忕殑璁捐鍙互鏀瑰彉榪欑鎯呭艦錛氬皢姣忎竴涓猲on-local static 瀵硅薄鎼埌鑷繁鐨勪笓灞炲嚱鏁板唴錛堣瀵硅薄鍦ㄦ鍑芥暟鍐呰澹版槑涓簊tatic錛夈傝繖浜涘嚱鏁拌繑鍥炰竴涓猺eference鐢ㄦ潵鎸囧悜浠栨墍鍖呭惈鐨勫璞°傜劧鍚庣敤鎴瘋皟鐢ㄨ繖浜涘嚱鏁幫紝鑰屼笉鏄洿鎺ユ寚娑夎繖浜涘璞°傛崲鍙ヨ瘽灝辨槸non-local static瀵硅薄琚玪ocal static瀵硅薄鏇挎崲浜嗐傝繖涓疄鐜扮殑鍩虹鍦ㄤ簬錛欳++淇濊瘉錛屽嚱鏁板唴鐨刵on-local static 瀵硅薄浼?xì)鍦ㄥ嚱鏁拌璋冪敤鏈熼棿棣枊啤閬囦笂璇ュ璞′箣瀹氫箟寮忔椂琚垵濮嬪寲銆傛墍浠ュ鏋滀互鍑芥暟璋冪敤鏇挎崲鐩存帴璁塊棶non-local static 瀵硅薄錛屽氨鑾峰緱浜嗕繚璇侊紝淇濊瘉鎵寰楃殑閭ｄ釜reference灝嗘寚鍚戜竴涓粡鍘嗗垵濮嬪寲鐨勫璞°?姝ゆ妧鏈疄鐜頒簬涓婇潰鐨勪唬鐮佸涓嬶細(xì)
class FileSystem{};//鍚屽墠FileSystem &tfs()//榪欎釜鍑芥暟鐢ㄦ潵鏇挎崲tfs瀵硅薄錛涗粬鍦‵ileSystem涓彲鑳芥槸涓猻tatic銆?/span>{static FileSystem fs;return fs;}class Directory{};Directory::Directory(){std::size_t disks = tfs().numDisks();}Directory &tempDir(){static Directory td;return td;}Things to remember:
1.Manually initialize objects of built-in type, because C++only sometimes initializes them itself;
2.In a constructor, prefer to use the member initialization list to assigenment inside the body of the constructor. List data member in the initialization list in the same order they're declared in the class.
3.Avoid initialization order problems across translation units by replacing non-local static objects with local static objects.
]]>
void f2(Widget const * pw);
const涔熷彲鐢ㄦ潵淇グSTL涓殑榪唬鍣ㄣ傚０鏄庤凱浠ｅ櫒涓篶onst灝辨兂澹版槑鎸囬拡涓篶onst涓鏍鳳紙鍗砊* const 鎸囬拡錛夛紝琛ㄧず榪欎釜榪唬鍣ㄤ笉寰楁寚鍚戜笉鍚岀殑涓滆タ銆備絾瀹冩墍鎸囩殑涓滆タ鐨勫兼槸鍙互鏀瑰彉鐨勩傚鏋滃笇鏈涜凱浠ｅ櫒鎵鎸囩殑涓滆タ涓嶅彲鏀瑰彉錛堝嵆妯℃嫙涓涓猚onst T*鎸囬拡錛夛紝闇瑕佺殑鏄痗onst_iterator:
std::vector<int> vec;
...
const std::vector<int>::iterator iter = vec.begin();// same as T* const
*iter = 10; //no problem
++iter; //wrong!!
std::vector<int>::const_iterator cIter = vec.begin();//same as const T*
*iter = 10; //wrong!!
++iter; //no problem
const 鏈鍏峰▉鍔涳紙錛燂級鐨勭敤娉曟槸闈㈠鍑芥暟澹版槑鏃剁殑搴旂敤銆傚湪涓涓嚱鏁板０鏄庡紡鍐咃紝const鍙互鍜屽嚱鏁拌繑鍥炲鹼紝鍚勫弬鏁幫紝鍑芥暟鑷韓錛堟垚鍛樺嚱鏁幫級浜х敓鍏寵仈銆?br>浠ゅ嚱鏁拌繑鍥炰竴涓父閲忓鹼紝寰寰鍙互闄嶄綆鍥犲鎴烽敊璇岄犳垚鐨勬剰澶栵紝鑰屽張涓嶈嚦浜庢斁寮冨畨鍏ㄦу拰楂樻晥鎬с備緥濡傦紝鑰冭檻鏈夌悊鏁扮殑operator*澹版槑寮忥細(xì)
class Rational(){...};
const Rational operator* (const Rational & lhs, const Rational & rhs);
涔熻浣犱細(xì)璇翠負(fù)浠涔堣繑鍥炰竴涓猚onst瀵硅薄錛熷師鍥犳槸濡傛灉涓嶈繖鏍峰埆浜哄彲鑳藉疄鐜拌繖鏍風(fēng)殑鏆磋錛?br>Rational a,b,c;
...
(a*b)=c;
涓嬮潰錛屼富瑕佽鏄巆onst浣滅敤浜庢垚鍛樺嚱鏁般?br>璁稿浜洪兘蹇借浜嗚繖涔堜竴涓簨瀹烇紝閭ｅ氨鏄鏋滀袱涓垚鍛樺嚱鏁板彧鏄父閲忔т笉鍚岋紝閭ｄ箞浠栦滑鏄彲浠ラ噸杞界殑銆傝冭檻浠ヤ笅榪欎釜鐢ㄦ潵琛ㄧず涓澶у潡鏂囧瓧鐨刢lass錛?br>
class TextBlock{public:const char& operator[](std::size_t position) const
{return text[position];}char& operator[](std::size_t position){return text[position];}private:std::string text;};TextBlock鐨刼perator[]鍙互榪欎箞浣跨敤錛?br>TextBlock tb("Hello");std::cout << tb[0]; //璋冪敤non-const const TextBlock ctb("Hello");std::cont << ctb[0]; //璋冪敤const鐪熸槸鎯呭艦涓璫onst瀵硅薄澶氱敤浜巔assed by pointer-to-const鎴杙assed by reference-to-const鐨勪紶閫掔粨鏋溿備笂榪扮殑ctb澶繃浜庨犱綔錛屼笅杈硅繖涓瘮杈冪湡瀹烇細(xì)
void print (const TextBlocd& ctb){ std::cout << ctb[0]; }鍙敤閲嶈澆operator[]騫跺涓嶅悓鐨勭増鏈粰浜堜笉鍚岀殑榪斿洖綾誨瀷錛屽氨鍙互浠onst鍜宯on-const鑾峰緱涓嶅悓鐨勫鐞嗐?br>姝ゅ闇瑕佹敞鎰忎竴鐐癸紝non-const operator[]鐨勮繑鍥炵被鍨嬫槸涓猺eference to char,涓嶆槸char銆傚鏋渙perator[]榪斿洖鐨勬槸涓猚har錛屼笅杈圭殑璧嬪煎氨涓嶈兘閫氳繃緙栬瘧錛?br>tb[0] = 'x'; //error c2106: ' = ' : left operand must be l-value
閭ｆ槸鍥犱負(fù)錛屽鏋滃嚱鏁扮殑榪斿洖綾誨瀷鏄釜鍐呯疆綾誨瀷錛岄偅涔堟敼鍔ㄥ嚱鏁扮殑榪斿洖鍊間粠鏉ュ氨涓嶅悎娉曘傜旱浣垮悎娉曪紝C++浠y value榪斿洖瀵硅薄榪欎竴浜嬪疄錛堟潯嬈?0錛夋剰鍛崇潃鏀瑰姩鐨勫叾瀹炲彧鏄痶b.text[0]鐨勪竴涓壇鏈紝涓嶆槸tb.text[0]鏈韓錛岄偅涓嶆槸鎴戜滑鎯寵鐨勭粨鏋溿?br>涓嬭竟鏉ヨ璇村湪const鍜宯on-const鎴愬憳鍑芥暟涓伩鍏嶉噸澶?br>鍋囪TextBlock錛堝拰CTextBlock錛夊唴鐨刼perator[]涓嶅崟鍙槸榪斿洖涓涓猺eference鎸囧悜鏌愬瓧絎︼紝涔熸墽琛岃竟鐣屾鏌ャ佸織璁拌闂俊鎭佺敋鑷沖彲鑳借繘琛屾暟鎹畬鏁存ф楠屻傛妸鎵鏈夎繖浜涘悓鏃舵斁榪沜onst鍜宯on-const operator[]涓紝瀵艱嚧榪欐牱鐨勪竴涓墿錛?br>
class TextBlock{public:const char& operator[](std::size_t position) const{ //杈圭晫媯(gè)鏌?bounds checking) //蹇楄鏁版嵁璁塊棶(log access data) //媯(gè)楠屾暟鎹畬鏁存?verify data integrity)return text[position];
}char& operator[](std::size_t position){ //杈圭晫媯(gè)鏌?bounds checking) //蹇楄鏁版嵁璁塊棶(log access data) //媯(gè)楠屾暟鎹畬鏁存?verify data integrity)return text[position];}private:std::string text;};class TextBlock{public:const char& operator[](std::size_t position) const{return text[position];}char& operator[](std::size_t position){const_cast<char&>(static_cast<const TextBlock&>(*this)[position]);}};鏈潯鐩葷粨錛?br>
Things to Remember
-
Declaring something const helps compilers detect usage errors. const can be applied to objects at any scope, to function parameters and return types, and to member functions as a whole.
-
Compilers enforce bitwise constness, but you should program using conceptual constness.
-
When const and non-const member functions have essentially identical implementations, code duplication can be avoided by having the non-const version call the const version.
]]>
銆?br>1.Case錛?define ASPECT_RATIO 1.653Recommendation錛歝onst double AspectRatio = 1.653錛?br>Reason: 褰撲嬌鐢ˋSPECT_RATIO浣嗘槸鑾峰緱涓涓紪璇戦敊璇俊鎭椂錛屽彲鑳戒綘浼?xì)寰堟槸鍙戝啅锛屽洜湄?fù)榪欎釜閿欒淇℃伅涔熻浼?xì)鎻愬?.653鑰屼笉鏄疉SPECT_RATIO銆傚鏋淎SPECT_RATIO瀹氫箟鍦ㄩ潪浣犳墍鍐欑殑澶存枃浠朵腑錛屼綘鏇存槸鍥犱負(fù)榪借釜浠栬屾氮璐規(guī)椂闂淬傛敼涓烘帹鑽愮殑鏂瑰紡鍚庯紝浣犳壘鍒扮殑鑲畾鏄疉spectRatio銆傚綋浠ュ父閲忔浛鎹?define鏃訛紝鏈変袱縐嶆敞鎰忕殑鎯呭喌錛岀涓縐嶆槸瀹氫箟甯擱噺鎸囬拡錛坈onst pointers錛夈傜敱浜庡父閲忓畾涔夊紡甯告斁鍦ㄥご鏂囦歡鍐咃紝鍥犳鏈夊繀瑕佸皢鎸囬拡涔熷０鏄庝負(fù)const銆備緥濡傚湪涓涓ご鏂囦歡鍐呭畾涔変竴涓父閲忕殑char*-based瀛楃涓詫紝蹇呴』鍐檆onst涓ゆ錛?br>const char* const authorName = "Edmund";
榪欓噷閲囩敤string瀵硅薄姣斿叾鍓嶈緢char*-based鏇村悎閫傦紝
const std::string authorName("Edmund");
絎簩縐嶆槸class涓撳睘甯擱噺銆備負(fù)浜嗗皢甯擱噺鐨勪綔鐢ㄥ煙闄愬埗鍦╟lass鍐咃紝浣犲繀欏昏浠栨垚涓篶lass鐨勪竴涓垚鍛橈紱鑰屼負(fù)紜繚姝ゅ父閲忓彧鏈変竴涓疄浣擄紝鍒欏繀欏誨０鏄庝負(fù)static錛?br>class GamePlayer{
private:
static const int NumTurns = 5;
int scores[NumTurns];
...
}
鐒惰岋紝浣犵湅鍒扮殑鏄疦umTurns鐨勫０鏄庡紡鑰屼笉鏄畾涔夊紡錛孋++閫氬父瑕佹眰鎴戜滑鎵浣跨敤鐨勪換浣曚笢瑗塊兘瑕佹湁涓涓畾涔夊紡錛屼絾濡傛灉浠栨槸涓猚lass鐨勪笓灞炲父閲忚屽張鏄痵tatic涓斾負(fù)鏁存暟綾誨瀷錛坕nts錛宑hars錛宐ools錛夛紝鍒欏仛鐗規(guī)畩澶勭悊銆傚彧瑕佷笉鍙栦粬浠殑鍦板潃錛屼綘鍙互澹版槑騫朵嬌鐢ㄤ粬浠屾棤闇鎻愪緵瀹氫箟寮忋備絾濡傛灉鍙栨煇涓猚lass涓撳睘甯擱噺鐨勫湴鍧錛屾垨綰典嬌涓嶅彇鍦板潃鑰岀紪璇戝櫒鍗村潥鎸佽鐪嬪埌涓涓畾涔夊紡錛屼綘灝卞繀欏繪彁渚涘彟澶栦竴涓畾涔夊紡錛?br>const int GamePlayer::NumTurns;
鐢變簬NumTurns鍦ㄥ０鏄庢椂宸茬粡鑾峰緱浜嗗垵鍊鹼紝鍥犳瀹氫箟鏃朵笉鍙互鍐嶈鍒濆箋傛澶栵紝瀵規(guī)墍璋撶殑“in-class鍒濆艱瀹?#8221;涔熷彧鍏佽瀵規(guī)暣鏁板父閲忚繘琛屻傚鏋滀負(fù)闈炴暣鍨嬪垯鍙互閲囩敤涓嬮潰鐨勮繖縐嶆柟寮忥細(xì)
class CostEstimate{
private:
static const double FudgeFactor;
...
}
const double CostEstimate::FudgeFactor = 1.35;
褰撲綘鍦ㄧ紪璇戞湡闇瑕佷竴涓猚lass甯擱噺鍊鹼紝渚嬪鍦ㄤ笂榪癎amePlayer::scores鐨勬暟緇勫０鏄庝腑錛屾鏃跺鏋滅紪璇戝櫒涓嶅厑璁?#8220;static鏁存暟鍨媍lass甯擱噺”瀹屾垚“in-class鍒濆艱瀹?#8221;錛屽彲閲囩敤enum鏉ヨВ鍐籌紝鍏剁悊璁哄熀紜鏄?#8220;涓涓睘浜庢灇涓劇被鍨嬬殑鏁板煎彲鏉冨厖ints琚嬌鐢?#8221;錛屼簬鏄疓amePlayer鍙畾涔夊涓嬶細(xì)
class GamePlayer{
private:
enum{NumTurns = 5};
int scores[NumTurns];
...
};
娉ㄦ剰錛氬彇涓涓猚onst鐨勫兼槸鍚堟硶鐨勶紝浣嗘槸鍙栦竴涓猠num鐨勫煎氨鏄笉鍚堟硶鐨勶紝鍙栦竴涓?define鐨勫間篃鏄笉鍚堟硶鐨勩傚鏋滀綘涓嶆兂璁╁埆浜鴻幏寰椾竴涓猵ointer鎴栬卹eference鎸囧悜浣犵殑鏌愪釜鏁存暟甯擱噺錛宔num鍙互甯姪浣犲疄鐜拌繖涓害鏉熴?br>涓嬭竟緇х畫璇撮澶勭悊鍣ㄣ傚彟澶栦竴涓父瑙佺殑#define璇敤鐨勬儏鏅槸浠ヤ粬鏉ュ疄鐜板畯錛屽畯鐪嬭搗鏉ュ儚鍑芥暟錛屼絾鏄笉浼?xì)鎷涜嚧鍑芥暟璋冪敤甯︽潵鐨勯澶栧紑閿錛屼緥濡傦細(xì)
#define CALL_WITH_MAX(a,b) f((a)>(b)?(a):(b))銆備粬鐨勭己鐐瑰氨涓嶈浜嗭紝鏇夸唬鏂瑰紡錛?br>template<class T> inline void callWithMax(const T& a, const T& b)
{
f(a > b?a : b);
}
鏈潯鐩葷粨錛?br>1.瀵逛簬鍗曠函甯擱噺錛屾渶濂戒互const瀵硅薄鎴栬卐nums鏇挎崲#defines錛?br>2.瀵逛簬褰技鍑芥暟鐨勫畯錛屾渶濂芥敼鐢╥nline鍑芥暟鏇挎崲#defines銆?br>
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