How can i pass a string as parameter for a thread in Windows?

Question

I'm studying threads in c++. I'm using the CreateThread() function from windows.h library:

#include <windows.h>
#include <iostream>
#include <unistd.h>


DWORD WINAPI ThreadFunc(void* data, std::string message) {
    std::cout<<message;
  return 0;
}

int main() {
  std::string saluti="hi";
  HANDLE thread = CreateThread(NULL, 0, ThreadFunc, &saluti, 0, NULL);
  sleep(5);
  
}

The error:

 error: invalid conversion from 'DWORD (__attribute__((__stdcall__)) *)(void*, std::__cxx11::string) {aka long unsigned int (__attribute__((__stdcall__)) *)(void*, std::__cxx11::basic_string<char>)}' to 'LPTHREAD_START_ROUTINE {aka long unsigned int (__attribute__((__stdcall__)) *)(void*)}' [-fpermissive]
   HANDLE thread = CreateThread(NULL, 0, ThreadFunc, &saluti, 0, NULL);
                                                                     ^

how can i pass a std::string to a thread function?

Answer 1

The thread start routine needs to have the signature:

DWORD __stdcall ThreadFunc(LPVOID lpThreadParameter);

So, you need to cast the void* into the pointer type which you sent into the function:

DWORD WINAPI ThreadFunc(LPVOID lpThreadParameter) {
    std::string& message = *static_cast<std::string*>(lpThreadParameter);
    std::cout<<message;
    return 0;
}

Just note that the string must not be destroyed while the thread is using it.