Question

Where does the pointer returned by calling string::c_str() point to ? In the following code snippet, I thought I will give get a segmentation fault but it gives me the correct output. If the pointer returned by string::c_str() points to an internal location inside the string object, then when the function returns and the object destructor gets invoked, I should get an invalid memory access.

#include <iostream>
#include <string>
using namespace std;

const char* func()
{
    string str("test");
    return str.c_str();
}

int main()
{
    const char* p = func();
    cout << p << endl;
    return 0;
}

Output: test
Compiler: g++ 4.3.3
Platform: ubuntu 2.6.28-19

Answer 1

Where does the pointer returned by calling string::c_str() point to?

It points to some place in memory where a null-terminated string containing the contents of the std::string is located.

The pointer is only valid until the std::string is modified or destroyed. It is also potentially invalidated if you call c_str() or data() again.

Basically, your safest bet is to assume the pointer obtained from c_str() is invalidated the next time you do something to the std::string object.

I should get an invalid memory access.

No, you get undefined behavior. You might get a memory access error of some kind (like a segmentation fault), but your program also might appear to continue running correctly. It might appear to work one time you run your program but fail the next.