C ++，调试断言失败

Question

Debug Assertion Failed

I spend a lot of time trying to fond out why I have an assert in this code.

If there is no string in the class, it's work well.

Can you explaine, why I have an Assert whit the class containing string.

Thank's Marc

#include <malloc.h>
#include <string>

class CTheClassWith_string
{
private:
    std::string TheName_;
};

class CTheClassWith_int
{
private:
    int TheName_;
};

int main()
{
std::string theString;
int size;

CTheClassWith_int   TheClassWith_int;
CTheClassWith_string TheClassWith_string;

CTheClassWith_int* pTheClassWith_int = new CTheClassWith_int;
size = _msize(pTheClassWith_int);
delete pTheClassWith_int;

CTheClassWith_string* pTheClassWith_string = new CTheClassWith_string;
size = _msize(pTheClassWith_string);
delete pTheClassWith_string;

CTheClassWith_int* pArrayTheClassWith_int = new CTheClassWith_int[2];
size = _msize(pArrayTheClassWith_int);
delete [] pArrayTheClassWith_int;

CTheClassWith_string* pArrayTheClassWith_string = new CTheClassWith_string[2];
size = _msize(pArrayTheClassWith_string);             // Why I assert on this line
delete [] pArrayTheClassWith_string;

return 0;
}

Answer 1

As from your question I understood you want to determine the size in bytes allocated from heap, when using new() or new[]() .

Well, you cannot use the _msize() function to achieve this. Besides it's a legacy function, the pointers obtained with new aren't necessarily coming from underlying calls to functions from the malloc() family (which _msize() relies on in turn, thus the assertion).

To determine sizes allocated from the heap (or elsewhere), you can always rely on the sizeof() operator:

CTheClassWith_int* pTheClassWith_int = new CTheClassWith_int;
size = sizeof(CTheClassWith_int);
delete pTheClassWith_int;

CTheClassWith_string* pTheClassWith_string = new CTheClassWith_string;
size = sizeof(CTheClassWith_string);
delete pTheClassWith_string;

CTheClassWith_int* pArrayTheClassWith_int = new CTheClassWith_int[2];
size = sizeof(CTheClassWith_int) * 2;
delete [] pArrayTheClassWith_int;

CTheClassWith_string* pArrayTheClassWith_string = new CTheClassWith_string[2];
size = sizeof(CTheClassWith_string) * 2;
delete [] pArrayTheClassWith_string;