Memory leak while using c++ string

Question

When i run valgrind on below program, it reports memory leak. Can you please explain the cause?

#include <string>
#include <iostream>

using namespace std;

int main()
{
    char * arr = (char *) ::operator new(sizeof(char));
    string s = arr;

    return 0;
}

1. What exactly happens on line string s = arr? does it make a copy of arr?

Answer 1

valgrind is right. You call new and don't call delete , hence you have a memory leak.

When you assign arr to s , the latter doesn't take ownership of the former; instead, it makes a copy. It is still your responsibility to free arr .

Answer 2

在代码末尾delete arr将处理内存泄漏。

Answer 3

Ownership of arr is not passed to s , it copies arr to s 's internal buffer. You should free memory with delete operator

Answer 4

I think you assumed string will take the ownership of arr and it's responsible for delete the arr . BUT IT IS WRONG.

string s = arr;

Just copies characters from arr until reaching to \\0 . So, you should delete arr yourself.

Answer 5

The new[] operator in C++ allocates memory dynamically. All such memory must be freed manually, by the programmer. This is done with the delete[] operator. If you don't delete memory which you allocated with new, you have created a memory leak.

More information on that topic can be found in this C++ FAQ .