Why does this program crash: passing of std::string between DLLs

Posted by msiemeri on Stack Overflow See other posts from Stack Overflow or by msiemeri
Published on 2010-02-23T22:01:53Z Indexed on 2010/04/09 15:23 UTC
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Hello together.

I have some trouble figuring out why the following crashes (MSVC9):

//// the following compiles to A.dll with release runtime linked dynamically
//A.h
class A {
  __declspec(dllexport) std::string getString();
};
//A.cpp
#include "A.h"
std::string A::getString() {
   return "I am a string.";
}

//// the following compiles to main.exe with debug runtime linked dynamically
#include "A.h"
int main() {
   A a;
   std::string s = A.getString();
   return 0;
} // crash on exit

Obviously (?) this is due to the different memory models for the executable and DLL. Could it be that the string A::getString() returns is being allocated in A.dll and freed in main.exe?

If so, why - and what would be a safe way to pass strings between DLLs (or executables, for that matter)? Without using wrappers like shared_ptr with a custom deleter.

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