Storing function pointer in std::function

Question

I\'m trying to write a C++0x wrapper around dlopen()/dlsym() to dynamically load functions from shared objects:

class DynamicLoader
{
  public:
    DynamicLoade         


        

Answer 1

You just need to cast result of dlsym() call to a proper type. Here's a complete working example:

#include 
#include 
#include 
#include 
#include 

class DynamicLoader
{
public:
    DynamicLoader(std::string const& filename) :
        m_handle(dlopen(filename.c_str(), RTLD_LAZY))
    {
        if (!m_handle)
        {
            throw std::logic_error("can't load library named \"" + filename + "\"");
        }
    }

    template
    std::function load(std::string const& functionName) const
    {
        dlerror();
        void* const result = dlsym(m_handle, functionName.c_str());
        if (!result)
        {
            char* const error = dlerror();
            if (error)
            {
                throw std::logic_error("can't find symbol named \"" + functionName + "\": " + error);
            }
        }

        return reinterpret_cast(result);
    }

private:
    void* const m_handle;
};

int main()
{
    DynamicLoader const loader("/lib64/libz.so.1");
    auto const zlibVersion = loader.load("zlibVersion");
    std::cout << "zlib version: " << zlibVersion() << std::endl;
    return 0;
}