CODEWITHSUNDEEP
c++stdloadlibrary
Anonymous
Anonymous

Reputation: 501

Function pointer obtained from GetProcAddress crashes the program if it uses the stdlib

I'm trying to dynamically load a dll and call a function from it at runtime. I have succeeded in getting a working pointer with GetProcAddress, but the program crashes if the function from the dll uses the stdlib. Here's the code from the executable that loads the dll:

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

typedef int (*myFunc_t)(int);

int main(void) {
  using namespace std;
  HINSTANCE dll = LoadLibrary("demo.dll");
  if (!dll) {
    cerr << "Could not load dll 'demo.dll'" << endl;
    return 1;
  }
  myFunc_t myFunc = (myFunc_t) GetProcAddress(dll, "myFunc");
  if (!myFunc) {
    FreeLibrary(dll);
    cerr << "Could not find function 'myFunc'" << endl;
    return 1;
  }
  cout << "Successfully loaded myFunc!" << endl;
  cout << myFunc(3) << endl;
  cout << myFunc(7) << endl;
  cout << myFunc(42) << endl;
  cout << "Successfully called myFunc!" << endl;
  FreeLibrary(dll);
  return 0;
}

Here's code for the dll that actually works:

#include <iostream>

extern "C" {

  __declspec(dllexport) int myFunc(int demo) {
    //std::cout << "myFunc(" << demo << ")" << std::endl;
    return demo * demo;
  }

}

int main(void) {
  return 0;
}

(Note that the main method in the dll code is just to appease the compiler)

If I uncomment the line with std::cout however, then the program crashes after the cout << "Sucessfully loaded myFunc!" << endl; line but before anything else gets printed. I know there must be some way to do what I want; what do I need to change for it to work?

Upvotes: 1

Views: 639

Answers (1)

Anonymous
Anonymous

Reputation: 501

As discussed in the comments, it turns out that the compiler's demands for a main function were hints that I was inadvertently making a an exe that decptively used the file extension dll, not an actual dll (because I didn't quite understand the compiler options I was using), which in some way messed up the dynamic loading of that assembly.

Upvotes: 1

Related Questions