Issue passing C-Strings in C++

Question

I'm not C++ developer and I'm trying to figure out why when I return a C-string from a function I'm getting garbage out.

#include <stdio.h>

const char* tinker(const char* foo);

int main(void)
{
    const char* foo = "foo";
    foo= tinker(foo);
    printf(foo); // Prints garbage
    return 0;
}

const char* tinker(const char* foo)
{
    std::string bar(foo);
    printf(bar.c_str());  // Prints correctly
    return bar.c_str();
}

Answer 1

You're returning a C-string that's based on the internal memory of a std::string. However, this is being printed AFTER your bar is destructed. This memory is garbage by the time it reaches the printf(foo); line.

Answer 2

You're returning a pointer to a buffer internal to bar, but then you're destroying bar (and the buffer) before you use that pointer.

If you need the content of bar after the function returns, return bar instead of bar.c_str().