Win32.hpp

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/* Copyright 2021 Jan Stephan
 *
 * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by
 * the European Commission - subsequent versions of the EUPL (the “Licence”).
 * You may not use this work except in compliance with the Licence.
 * You may obtain a copy of the Licence at:
 *
 *     http://ec.europa.eu/idabc/eupl.html
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the Licence is distributed on an “AS IS” basis, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 *  Licence permissions and limitations under the Licence.
 */
 
#ifdef _WIN32
 
#    include <windows.h>
 
#    include <cstdio>
#    include <string>
#    include <system_error>
 
namespace bactria
{
    namespace system
    {
        // HMODULE <- HINSTANCE <- HANDLE <- PVOID <- void*
        using plugin_handle_t = HMODULE;
 
        [[nodiscard]] auto make_last_error_string() -> std::string
        {
            const auto code = std::error_code{GetLastError(), std::system_category()};
            return code.message();
        }
 
        [[nodiscard]] auto open_plugin(const char* path) -> plugin_handle_t
        {
            auto handle = LoadLibrary(path);
            if(handle != nullptr)
                return handle;
 
            throw std::runtime_error{make_last_error_string()};
        }
 
        template<typename Sig>
        auto load_func(plugin_handle_t handle, Sig& ptr, const char* name) -> void
        {
            if(ptr == nullptr)
            {
                ptr = reinterpret_cast<Sig>(GetProcAddress(handle, name));
                if(ptr == nullptr)
                    throw std::runtime_error{make_last_error_string()};
            }
        }
 
        auto close_plugin(plugin_handle_t handle) noexcept -> void
        {
            if(handle == nullptr)
                return;
 
            auto err = FreeLibrary(handle);
            if(err == 0)
            {
                auto errstr = make_last_error_string();
                if(!errstr.empty())
                    std::fprintf(stderr, "WARNING: Error while closing plugin library: %s\n", errstr.c_str());
                else
                    std::fprintf(stderr, "WARNING: Unknown error while closing plugin library.\n");
            }
        }
    } // namespace system
} // namespace bactria
 
#endif // _WIN32