浅拷贝和深拷贝,以及push_back()的奥秘【转】
using namespace std;
class CDemo{
public:
CDemo():str(NULL){};
~CDemo()
{
if(str)
delete [] str;
};
char *str;
};
int main(int argc, char ** argv)
{
CDemo d1;
d1.str = new char[32];
strcpy(d1.str, "trend micro");
vector<CDemo> *a1 = new vector<CDemo>();
a1->push_back(d1);
delete a1;
return 0;
}
编译能通过
解答:默认的拷贝构造只是成员拷贝,于是两个对象str的值相同,两次析构delete了相同的str,解决办法是弄一个拷贝构造函数,里边strdup一下str。其实这也就是浅拷贝和深拷贝的区别。
须改成:
using namespace std;
class CDemo{
public:
CDemo():str(NULL){};
CDemo(const CDemo &temp)
{
str = new char[strlen(temp.str) + 1];
strcpy(str, temp.str);
}
~CDemo()
{
if(str)
delete [] str;
};
char *str;
};
int main(int argc, char ** argv)
{
CDemo d1;
d1.str = new char[32];
strcpy(d1.str, "trend micro");
vector<CDemo> *a1 = new vector<CDemo>();
a1->push_back(d1);
delete a1;
return 0;
}
其实还有人觉得疑惑,为什么push_back的函数原型为:
void push_back(const _Ty& _Val)
参数是引用传递的,那为什么还会调用拷贝构造函数呢,这个秘密在于push_back内部还调用了另一个函数insert(),而insert()函数则调用了拷贝构造函数:
void push_back(const _Ty& _Val)
{ // insert element at end
if (size() < capacity())
#if _HAS_ITERATOR_DEBUGGING
{ // room at end, construct it there
_Orphan_range(_Mylast, _Mylast);
_Mylast = _Ufill(_Mylast, 1, _Val);
}
#else
_Mylast = _Ufill(_Mylast, 1, _Val);
#endif
else
insert(end(), _Val);
}