Thread: Dynamic loading with C++

I have problem with dynamic loading function with C++ (in C it works).
Let test.cpp be

Code:

#include <iostream>
#include <string>

using namespace std;

void f(string s)
{
  cout << s << endl;
}

and main.cpp

Code:

#include <dlfcn.h>
#include <string>

using namespace std;

extern "C" void f(string);
 
int main()
{
  void* handle = dlopen("libtest.so", RTLD_LAZY);
  void (*test)(string) = dlsym(handle, "f");
  (*test)("Hello, World!");
  dlclose(handle); 
}

Then, I made libtest.so with

Code:

g++ -c test.c
g++ -shared -fPIC -o libtest.so test.o

put it into /usr/lib and set appropriate file attributes. But,

Code:

g++ -ldl main.cpp

gives error main.cpp:12: error: invalid conversion from `void*' to `void (*)(std::string)'.
Why? Same thing works in C with char* and printf() instead of string and cout.

If I cast it with

Code:

void (*test)(string) = (void (*)(string))dlsym(handle, "f");

then it compiles but on run gives Segmentation fault.

After some experimenting I think the easiest way is to declare the exported function in the dynamic libarary as extern "C", and use it as extern "C" as well. This way there are no namemangling issues.
Kurt

extern declaration must be placed into f's definition in the test.cpp and removed from main.cpp.
Thanks for the help, especially for the URL about pointer conversions.