Fixing undefined reference to dlopen and dlcose

问题

I have created simple c++ application. I can compile it and t works fine. But now I need to load library dynamically and I have added dlfnc.h to my project and added some more code:

#include <iostream>
#include <dlfcn.h>
void *mylib;
int eret;

using namespace std;

int main() {

    mylib = dlopen("mylib.so", RTLD_LOCAL | RTLD_LAZY);
    eret = dlclose(mylib);

    cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
    return 0;
}

Compiling:

myname@ubuntu:~/workspace/LinuxGcc/src$ g++ LinuxGcc.cpp 

And got compilation error:

/tmp/ccxTLiGY.o: In function `main':
LinuxGcc.cpp:(.text+0xf): undefined reference to `dlopen'
LinuxGcc.cpp:(.text+0x25): undefined reference to `dlclose'
collect2: error: ld returned 1 exit status

dlfcn.h exist in /usr/include/

Where is problem?

回答1:

dlopen(3):

   Link with -ldl.

so

g++ LinuxGcc.cpp -ldl

will be ok.

回答2:

The solution is very simple. Add the -ldl flag for linking.

回答3:

In case of bazel build system linkopts = ['-ldl']

来源：https://stackoverflow.com/questions/33035712/fixing-undefined-reference-to-dlopen-and-dlcose