README.md

Dylib - Dynamic Library Loader for C++

The goal of this C++ Library is to load dynamic libraries (.so, .dll, .dylib) and access its functions and global variables at runtime.

Compatibility

Works on Linux, Windows, MacOS

Installation

Click HERE to download the dylib header file
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Documentation

Dylib Class

The dylib class can load a dynamic library at runtime:

dylib lib("./myDynLib.so");

The dylib class can detect the file extension of the actual os using dylib::extension:

dylib lib("./myDynLib", dylib::extension);

or

dylib lib;
lib.open("./myDynLib", dylib::extension);

Open and Close

open
Load a dynamic library into the object. If a dynamic library was already opened, it will be unloaded and replaced

close
Close the dynamic library currently loaded in the object. This function will be automatically called by the class destructor

// Load ./myDynLib.so

dylib lib("./myDynLib.so");

// Unload ./myDynLib.so and load ./otherLib.so

lib.open("./otherLib.so");

// Close ./otherLib.so

lib.close();

Get a Function or a Variable

get_function
Get a function from the dynamic library currently loaded in the object.

get_variable
Get a global variable from the dynamic library currently loaded in the object.

// Load ./myDynLib.so

dylib lib("./myDynLib.so");

// Get the global function adder

auto adder = lib.get_function<double(double, double)>("adder");

// Get the global variable pi_value

double pi = lib.get_variable<double>("pi_value");

// Use the function adder with pi_value

double result = adder(pi, pi);

Dylib Exceptions

handle_error
This exception is raised when the library failed to load or the library encountered symbol resolution issues

symbol_error
This exception is raised when the library failed to load a symbol. This usually happens when you forgot to put DYLIB_API before a library function or variable

Those exceptions inherit from dylib::exception

try {
    dylib lib("./myDynLib.so");
    double pi_value = lib.get_variable<double>("pi_value");
    std::cout << pi_value << std::endl;
}
catch (const dylib::exception &e) {
    std::cerr << e.what() << std::endl;
    return EXIT_FAILURE;
}
return EXIT_SUCCESS;

Example

Let's write some functions in our forthcoming dynamic library:

// myDynLib.cpp

#include <iostream>
#include "dylib.hpp"

DYLIB_API double pi_value = 3.14159;
DYLIB_API void *ptr = (void *)1;

DYLIB_API double adder(double a, double b)
{
    return a + b;
}

DYLIB_API void print_hello()
{
    std::cout << "Hello!" << std::endl;
}

Let's build our code into a dynamic library:

g++ -std=c++11 -fPIC -shared myDynLib.cpp -o myDynLib.so

Let's try to access the functions and global variables of our dynamic library at runtime with this code:

// main.cpp

#include <iostream>
#include "dylib.hpp"

int main()
{
    try {
        dylib lib("./myDynLib.so");

        auto adder = lib.get_function<double(double, double)>("adder");
        std::cout << adder(5, 10) << std::endl;

        auto printer = lib.get_function<void()>("print_hello");
        printer();

        double pi_value = lib.get_variable<double>("pi_value");
        std::cout << pi_value << std::endl;

        auto &ptr = lib.get_variable<void *>("ptr");
        if (ptr == (void *)1)
            std::cout << "1" << std::endl;
    }
    catch (const dylib::exception &e) {
        std::cerr << e.what() << std::endl;
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

Let's build and run our code:
g++ -std=c++11 main.cpp -o out -ldl
./out

Output:

15
Hello!
3.14159
1

Tips

If you use CMake to build a dynamic library, running the below CMake rule will allow you to remove the prefix lib for macOS and linux, ensuring that the library shares the same name on all the different OS:

set_target_properties(target PROPERTIES PREFIX "")

Results

	Without CMake rule	With CMake rule
Linux	libmalloc.so	malloc.so
MacOS	libmalloc.dylib	malloc.dylib
Windows	malloc.dll	malloc.dll