Question

I have a class A with a functionvoid runThread() to call new thread. This is my A.cpp with struct SendInfo and function void thread(...) are not included in header file A.h:

//A.cpp
struct SendInfo{
   int a;
   std::string mess;
   SendInfo(int _a, std::string _mess){
      a = _a;
      mess = _mess;
   }
};

void thread(SendInfo* args){
   std::cout << args->mess << std::endl; // Result here is nothing :-?
}

void A::runThread(){
   SendInfo info(10,"dump_string");
   std::cout << info.mess << std::endl; // Result here is "dump_string"
   _beginthread((void(*)(void*))thread, 0, &info);
}

When in main function, i call runThread() of A object, the result of info.mess is good, but args->mess have no string. So what’s my problem? and how to solve it?

Answer 1

You are using the local variable info; as soon as runThread exits, this variable goes out of scope and you must no longer access it, even from the other thread.

You need to ensure info has a lifetime which extends until the end of your thread function (or at least, until you’ve accessed it for the last time in thread).