#include<iostream>
using std::cout;
using std::endl;
class CDust{
public:
CDust()
{
cout << " CDust constructor " << endl;
}
~CDust()
{
cout << " ~CFoo destructor " << endl;
}
};
CDust A;
int main()
{
return 0;
}
我想類似的代碼在網(wǎng)上Google下應(yīng)該有不少
嘗試了下,在vc6.0的情況下,是沒有輸出 "~CFoo destructor", 但這并不代表 ~CDust() 沒有執(zhí)行.
在~CDust里面設(shè)置斷點,會發(fā)現(xiàn)事實上程序運行時進入了析構(gòu)函數(shù)里 // -_! 表達(dá)好牽強
本來想實在跟蹤這里開始程序發(fā)生了什么調(diào)用了什么,發(fā)現(xiàn)功底不足,完全不明白,就先打斷了
而再在' return 0 ' 語句前面加上斷點,會看到這個新加的斷點比析構(gòu)里面的斷點先到達(dá),...
以現(xiàn)在c++的造詣和vc6.0的了解情況來看,頭痛了
為什么 return 0 后程序不是正常結(jié)束了才去執(zhí)行 全局對象的析構(gòu)?
改寫下代碼
#include<iostream.h>
class CDust{
public:
CDust()
{
cout << " CDust constructor " << endl;
}
~CDust()
{
cout << " ~CFoo destructor " << endl;
}
};
CDust A;
int main()
{
return 0;
}
這樣用舊版本的頭文件實現(xiàn),控制臺輸出了意外的兩個調(diào)用 --- 析構(gòu)函數(shù)輸出顯示了..
是cout在頭文件的實現(xiàn)方式不同?
在dev-c++里面,運行第一代代碼
根據(jù)斷點的設(shè)置測試,也是先執(zhí)行了 main()函數(shù)里面的 return 0 才進入全局函數(shù)的析構(gòu),也能發(fā)現(xiàn)析構(gòu)函數(shù)里面的輸出被調(diào)用了,控制臺有明確的顯示
這樣一來,又不明白了...
在vc6.0里面為什么執(zhí)行了全局函數(shù)的析構(gòu)卻沒有所謂的輸出?
是因為cmd控制臺在'return 0'程序權(quán)限收回 // 好像扯到系統(tǒng)的一些混亂的舊記憶了...
網(wǎng)游了一下
找到暫時比較清晰的說法是:
In C++, the constructor of a global object is executed before the
main() function(of course after the STARTUP code), while the destructor
is invoked after the main() function. So in my humble opinion, the
main() function is a bridge between the constructor and the
destructor.Further more, the constructor and the destructor is the
actual manager of the whole program, because they can manage all the
resources of the program(for instance, the constructor allocate memory
units and the destructor free them.I'am not sure of this, any comments
will be appreciated in advance.).
4)In C++, is it true that the resources obtained during the constructor
and the destructor (both belong to a global object)are managed by
themselves and have nothing with the main() function.Therfore, I think
the main() function is not the king in C++ as it is in C.
//感謝提出此說法的朋友
_startup才是用戶程序的起點和終點? 的確,調(diào)用_exit()函數(shù)再斷點測試,全局對象的destructor是沒有進入的機會 //長見識了
就此先打斷... 再深入今晚就這樣完了.
就此記錄下,以后再接觸
不小心又接觸了...
懶得開新的就集中在這里吧
在main()里面手動調(diào)用全局對象的析構(gòu), 最后程序都會執(zhí)行兩次析構(gòu)調(diào)用... 在<iostream.h>的cout這種情況下明顯,在std::cout下還得靠斷點設(shè)置才能體現(xiàn)到(vc6的情況)
這里是一種解析
{
Once a destructor is invoked for an object, the object no longer exists; the behavior is undefined if the destructor is invoked for an object whose lifetime has ended. [Example: if the destructor
for an automatic object is explicitly invoked, and the block is
subsequently left in a manner that would ordinarily invoke implicit
destruction of the object, the behavior is undefined
}
非global static object 也會出現(xiàn)兩次調(diào)用, 區(qū)別只在與一個在main() 退出之前,一個在之后...
(的確,手工調(diào)用析構(gòu)函數(shù)的情況很少出現(xiàn) -_! )
如果我在析構(gòu)里面存在 釋放內(nèi)存 這一類實現(xiàn), 那第二次再次釋放不是容易出問題!!!
以后遇到這種情況得注意檢測代碼的添加...