I have some old C code that I would like to combine with some C++ code.
The C code used to have has the following includes:
#include <windows.h>
#include <stdio.h>
#include <string.h>
#include "mysql.h"
Now I'm trying to make it use C++ with iostream like this:
#include <windows.h>
#include <stdio.h>
#include <string>
#include <iostream>
#include "mysql.h"
But I keep getting the following linker errors when I compile:
[Linker error] undefined reference to `std::string::size() const'
[Linker error] undefined reference to `std::string::operator[](unsigned int) const'
[Linker error] undefined reference to `std::string::operator[](unsigned int) const'
[Linker error] undefined reference to `std::string::operator[](unsigned int) const'
[Linker error] undefined reference to `std::ios_base::Init::Init()'
[Linker error] undefined reference to `std::ios_base::Init::~Init()'
ld returned 1 exit status
How do I resolve this?
Edit: My compiler is Dev-C++ 4.9.9.2
The C string.h
header and the C++ string
header are not interchangeable.
Overall, though, your problem is that the file is getting properly compiled, but the wrong runtime library is getting linked in.
Dev-C++ uses GCC. GCC can correctly determine the language in a file based on file extension, but won't link the right runtime library in unless you specifically ask it to (-lstdc++
at the command line). Calling GCC as "g++
" (or, in your case, "mingwin32-g++
") will also get the right language and will link the needed library.