DllLoader.h

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/* Copyright (C) 2011 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_DLLLOADER
#define INCLUDED_DLLLOADER

#include "ps/Errors.h"

ERROR_GROUP(DllLoader);
ERROR_TYPE(DllLoader, DllNotLoaded);
ERROR_TYPE(DllLoader, SymbolNotFound);

class DllLoader
{
public:
    /**
     * Prepare the DLL loader. Does no actual work.
     *
     * @param name base name of the library (from which we'll derive
     *  "name.dll", "libname_dbg.so", etc). Pointer must remain valid for
     *  this object's lifetime (which is fine if you just use a string literal).
     */
    DllLoader(const char* name);

    ~DllLoader();

    /**
     * Attempt to load and initialise the library, if not already. Can be harmlessly
     * called multiple times. Returns false if unsuccessful.
     */
    bool LoadDLL();

    /**
     * Check whether the library has been loaded successfully. Returns false
     * before {@link #LoadDLL} has been called; otherwise returns the same as
     * LoadDLL did.
     */
    bool IsLoaded() const;

    /**
     * Unload the library, if it has been loaded already. (Usually not needed,
     * since the destructor will unload it.)
     */
    void Unload();
    
    /**
     * Attempt to load a named symbol from the library. If {@link #IsLoaded} is
     * false, throws PSERROR_DllLoader_DllNotLoaded. If it cannot load the
     * symbol, throws PSERROR_DllLoader_SymbolNotFound. In both cases, sets fptr
     * to NULL. Otherwise, fptr is set to point to the loaded function.
     *
     * @throws PSERROR_DllLoader
     */
    template <typename T>
    void LoadSymbol(const char* name, T& fptr) const;

    /**
     * Override the build-time setting of the directory to search for libraries.
     */
    static void OverrideLibdir(const char* libdir);

private:
    // Typeless version - the public LoadSymbol hides the slightly ugly
    // casting from users.
    void LoadSymbolInternal(const char* name, void** fptr) const;

    const char* m_Name;
    void* m_Handle;
};

template <typename T>
void DllLoader::LoadSymbol(const char* name, T& fptr) const
{
    LoadSymbolInternal(name, (void**)&fptr);
}

#endif // INCLUDED_DLLLOADER