未使用的变量 'class' [-Wunused-变量] - 错误/警告

Question

我在c++中使用SDL完成了这个项目。

我在编译时得到这个错误，我不知道如何修复它。

它说:

Source/Classes/game.cpp:15:15: advarsel(this means 'warning' in danish): unused variable 'imagemanager' [-Wunused-variable]

但是imagemanager是一个类?这是导致错误的行:

Imagemanager imagemanager; // Init's class Imagemanager

它位于文件'game.cpp'的第15行

这是'Imagemanager';

class Imagemanager
{
friend class Player;
private:
public:
SDL_Surface* load_image( std::string filename ); // Loads images
//Apply a surface to another. Often used for applying surface to display
int apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip );
};

这是在另一个文件中定义的，但它被正确地包含。

编辑:忘了说我正在使用这个类，但编译器说，当我使用它，它没有定义我在这里使用imagemanager:

surface = imagemanager.load_image("player.png";);

在另一个名为

的类中

Player

，初始化为

player 

两个类(imagemanager和player)都在Game类的构造函数中初始化，Game类在main中初始化。我在player中使用imagemanager，并计划在其他地方也使用它。主文件:

#include <windows.h>
#include <string>
#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "Classes/game.cpp"
int main( int argc, char* args[] ) 
{
    Game game;
    game.initialize(); // Initializes the rest of game
    game.go(); // Starts the game
    return 0; // Ends the program
}

Game.cpp的构造函数+头文件:

#ifndef _GAME_
#define _GAME_
#include "imagemanager.cpp"
#include "player.cpp"
#include "timer.cpp"
#include "game.h"
Game::Game()
{
    screenDimension.w = 940; // Width  of the initialized window
    screenDimension.h = 540; // Height of the initialized window
    useFrameCap = true; // Tells the frame cap wether to activate or not
    quitGame = false; // Tells the main loop to quit if true
        FPS = 60; // Frames per second. Used by the frame cap.
    Imagemanager imagemanager; // Inits class Imagemanager
    Player player; // Inits class Player
    Timer timer; // Inits class Timer
    Game game; // Inits class Game
}

之后在"game.go()"中，我调用了函数"player.render()"，之后调用了"player.update()"。":

if ( RunJumpF )
    {
        RunJumpF = player.jump();
    }

当右键被按下或者当函数想在下一个刻度

运行时，RunJumpF将变为true

在所有其他的计算之后，我调用:

player.update();

我的player.cpp文件的实际功能如下所示:

#ifndef __PLAYER__
#define __PLAYER__
#include <string>
#include "player.h"
Player::Player()
{
    surface = imagemanager.load_image("player.png";); // Loads the player tile and saves into the surface 'surface'
    if (surface == NULL) // in case something went wrong in loading the player, tell the user
    {
        SDL_WM_SetCaption("ERROR LOADING PLAYER!", NULL); // I know there are better ways to do this but i'll look at that later
    }
    needsUpdate = true;
}
bool Player::jump()
{
    move.x = move.x + 3; // Moves the player X pixels right, next time the player updates
    needsUpdate = true; // Tells the program to update the player
    return true; // Tells the program that this function isn't done and it will be run next tick
}
int Player::update()
{
    if ( needsUpdate )
    {
        pos.x = pos.x + move.x;
        pos.y = pos.y + move.y;
        move.x = 0;
        move.y = 0;
        render(); // This calculates the position of the player and blits the player to the display
        return 1; // If no errors were discovered return 1;
    } else {
        render();
        return -1; // If no need to update, returns -1
    }
}
bool Player::render()
{
        if (SDL_BlitSurface( surface, NULL, display, pos ) != 0)
        {
            SDL_WM_SetCaption("ERROR BLITTING PLAYER!", NULL); // Tells the user that shit gone wrong
            return false;
        }
        return true
}
#endif

Answer 1

这是警告，不是错误。由于您不使用imagemanager对象，而只是声明它，因此会出现此警告。你可以用for example(void)imagemanager;，或者真正使用这个对象(不要注意这个警告，直到你开发应用程序)，警告将消失。

编辑:告诉我们这个对象的用法如何?

Answer 2

imagemanager是Imagemanager类型的变量(对象)。

所以，警告是正确的。在代码的某个地方使用imagemanager，或者删除这行。

还要注意，c++是区分大小写的，所以Imagemanager和imagemanager之间是有区别的。

一个是代码中的类，另一个是该类型的对象。