SDL2 - 应该返回 True 的函数评估为 False
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【中文标题】SDL2 - 应该返回 True 的函数评估为 False【英文标题】：SDL2 - function supposed to return True evaluates to False 【发布时间】：2019-12-17 15:25:48 【问题描述】：我正在使用 SDL2，遵循 LazyFoo 的教程。我已经到了加载 TTF 字体部分，而且我似乎遵循了他所做的一切，除了添加两个额外的 TTF_Font 和 SDL_Renderer 参数
bool LTexture::loadFromRenderedText(TTF_Font *&gFont, std::string textureText, SDL_Color textColor, SDL_Renderer *&gRenderer)
//Get rid of preexisting texture
free();
//Render text surface
SDL_Surface* textSurface = TTF_RenderText_Solid( gFont, textureText.c_str(), textColor );
if( textSurface == NULL )
printf( "Unable to render text surface! SDL_ttf Error: %s\n", TTF_GetError() );
else
//Create texture from surface pixels
mTexture = SDL_CreateTextureFromSurface( gRenderer, textSurface );
if( mTexture == NULL )
printf( "Unable to create texture from rendered text! SDL Error: %s\n", SDL_GetError() );
else
//Get image dimensions
mWidth = textSurface->w;
mHeight = textSurface->h;
//Get rid of old surface
SDL_FreeSurface( textSurface );
return 1;
这是函数，也是它的调用位置：
gFont = TTF_OpenFont( "Font/comicSans.ttf", 28 );
if( gFont == NULL )
printf( "Failed to load COMIC_SANS font! SDL_ttf Error: %s\n", TTF_GetError() );
success = false;
else
//Render text
SDL_Color textColor = 0, 0, 0 ;
if( !gTextTexture.loadFromRenderedText(gFont, "Hello I am hot", textColor, gRenderer));
printf( "Failed to render text texture!\n" );
success = false;
如果succes 为假，程序会打印“加载媒体失败”
这是我从运行程序得到的输出，注意没有实际的 SDL 或 TTF 错误，只有当loadFromRendereredText 返回 false 时出现的错误，它没有，因为我已将其设置为返回1：
Failed to render text texture!
Failed to load media!
我的文件和 LazyFoo 的文件的唯一实际区别是我的 LTexture 类与主文件位于一个单独的文件中，这就是为什么由于某种原因我不能使用 gFont 和 gRenderer（全局变量）
知道是什么原因造成的吗？
完整代码：
main.cpp:
/*This source code copyrighted by Lazy Foo' Productions (2004-2019)
and may not be redistributed without written permission.*/
//Using SDL and standard IO
#include <SDL.h>
#include <SDL_image.h>
#include <SDL_ttf.h>
#include <stdio.h>
#include <string>
#include "LTexture.h"
bool init();
bool loadMedia();
void close();
//The window we'll be rendering to
SDL_Window* gWindow = NULL;
SDL_Renderer* gRenderer = NULL;
//The surface contained by the window
SDL_Surface* gScreenSurface = NULL;
TTF_Font *gFont = NULL;
LTexture gTextTexture;
//Screen dimension constants
const int SCREEN_WIDTH = 500;
const int SCREEN_HEIGHT = 500;
int main(int argc, char* args[])
//Start up SDL and create window
if( !init() )
printf( "Failed to initialize!\n" );
else
//Load media
if( !loadMedia() )
printf( "Failed to load media!\n" );
else
//Main loop flag
bool quit = false;
//Event handler
SDL_Event event;
//While application is running
while( !quit )
//Handle events on queue
while( SDL_PollEvent( &event ) != 0 )
//User requests quit
if( event.type == SDL_QUIT )
quit = true;
//Clear screen
SDL_SetRenderDrawColor(gRenderer, 0xFF, 0xFF, 0xFF, 0xFF);
SDL_RenderClear( gRenderer );
gTextTexture.render(gRenderer, (SCREEN_WIDTH - gTextTexture.getWidth()) / 2, (SCREEN_HEIGHT - gTextTexture.getHeight()) / 2);
//Update screen
SDL_RenderPresent( gRenderer );
//Free resources and close SDL
close();
return 0;
bool init()
//Initialization flag
bool success = true;
//Initialize SDL
if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
printf( "SDL could not initialize! SDL_Error: %s\n", SDL_GetError() );
success = false;
else
//Create window
gWindow = SDL_CreateWindow( "SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
if( gWindow == NULL )
printf( "Window could not be created! SDL Error: %s\n", SDL_GetError() );
success = false;
else
//Create renderer for window
gRenderer = SDL_CreateRenderer( gWindow, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
if( gRenderer == NULL )
printf( "Renderer could not be created! SDL Error: %s\n", SDL_GetError() );
success = false;
else
//Initialize renderer color
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
//Initialize PNG loading
int imgFlags = IMG_INIT_PNG;
if( !( IMG_Init( imgFlags ) & imgFlags ) )
printf( "SDL_image could not initialize! SDL_image Error: %s\n", IMG_GetError() );
success = false;
//Initialize SDL_ttf
if( TTF_Init() == -1 )
printf( "SDL_ttf could not initialize! SDL_ttf Error: %s\n", TTF_GetError() );
success = false;
return success;
bool loadMedia()
//Loading success flag
bool success = true;
//Open the font
gFont = TTF_OpenFont( "Font/comicSans.ttf", 28 );
if( gFont == NULL )
printf( "Failed to load COMIC_SANS font! SDL_ttf Error: %s\n", TTF_GetError() );
success = false;
else
//Render text
SDL_Color textColor = 0, 0, 0 ;
if( !gTextTexture.loadFromRenderedText(gFont, "Hello I am hot", textColor, gRenderer));
printf( "Failed to render text texture!\n" );
success = false;
return success;
void close()
//Free loaded images
gTextTexture.free();
//Destroy window
SDL_DestroyRenderer( gRenderer );
SDL_DestroyWindow( gWindow );
TTF_CloseFont(gFont);
gWindow = NULL;
gRenderer = NULL;
gFont = NULL;
//Quit SDL subsystems
TTF_Quit();
IMG_Quit();
SDL_Quit();
LTexture.h：
#ifndef LTEXTURE_INCLUDED
#define LTEXTURE_INCLUDED
#include <SDL.h>
#include <SDL_image.h>
#include <SDL_ttf.h>
#include <stdio.h>
#include <string>
//Texture wrapper class
class LTexture
public:
//Initializes variables
LTexture();
//Deallocates memory
~LTexture();
//Loads image at specified path
bool loadFromFile( std::string path, SDL_Renderer *&gRenderer);
//Loads image from string text
bool loadFromRenderedText(TTF_Font *&gFont, std::string textureText, SDL_Color textColor, SDL_Renderer *&gRenderer);
//Deallocates texture
void free();
//Set color modulation
void setColor( Uint8 red, Uint8 green, Uint8 blue );
//Set blending
void setBlendMode( SDL_BlendMode blending );
//Set alpha modulation
void setAlpha( Uint8 alpha );
//Renders texture at given point
void render(SDL_Renderer *&gRenderer, int x, int y, SDL_Rect *clip = NULL, double angle = 0.0, SDL_Point* center = NULL, SDL_RendererFlip flip = SDL_FLIP_NONE );
//Gets image dimensions
int getWidth()return mWidth;
int getHeight()return mHeight;
private:
//The actual hardware texture
SDL_Texture* mTexture;
//Image dimensions
int mWidth;
int mHeight;
;
#endif // LTEXTURE_INCLUDED
LTexture.cpp:
#include "LTexture.h"
LTexture::LTexture()
mTexture = NULL;
mWidth = 0;
mHeight = 0;
LTexture::~LTexture()
//Deallocate resources
free();
bool LTexture::loadFromFile(std::string path, SDL_Renderer *&gRenderer)
free();
SDL_Texture* newTexture = NULL;
SDL_Surface *loadedSurface = IMG_Load(path.c_str());
if(loadedSurface == NULL)
printf("Unable to load image %s! SDL_image Error: %s\n", path.c_str(), IMG_GetError());
else
//Color key image
SDL_SetColorKey( loadedSurface, SDL_TRUE, SDL_MapRGB( loadedSurface->format, 0, 0xFF, 0xFF ) );
newTexture = SDL_CreateTextureFromSurface(gRenderer, loadedSurface);
if(newTexture == NULL)
printf( "Unable to create texture from %s! SDL Error: %s\n", path.c_str(), SDL_GetError() );
else
mWidth = loadedSurface->w;
mHeight = loadedSurface->h;
SDL_FreeSurface( loadedSurface );
mTexture = newTexture;
return mTexture != NULL;
bool LTexture::loadFromRenderedText(TTF_Font *&gFont, std::string textureText, SDL_Color textColor, SDL_Renderer *&gRenderer)
//Get rid of preexisting texture
free();
//Render text surface
SDL_Surface* textSurface = TTF_RenderText_Solid( gFont, textureText.c_str(), textColor );
if( textSurface == NULL )
printf( "Unable to render text surface! SDL_ttf Error: %s\n", TTF_GetError() );
else
//Create texture from surface pixels
mTexture = SDL_CreateTextureFromSurface( gRenderer, textSurface );
if( mTexture == NULL )
printf( "Unable to create texture from rendered text! SDL Error: %s\n", SDL_GetError() );
else
//Get image dimensions
mWidth = textSurface->w;
mHeight = textSurface->h;
//Get rid of old surface
SDL_FreeSurface( textSurface );
return 1;
void LTexture::free()
if(mTexture != NULL)
SDL_DestroyTexture(mTexture);
mTexture = NULL;
mWidth = 0;
mHeight = 0;
void LTexture::setColor( Uint8 red, Uint8 green, Uint8 blue )
//Modulate texture
SDL_SetTextureColorMod( mTexture, red, green, blue );
void LTexture::setBlendMode( SDL_BlendMode blending )
//Set blending function
SDL_SetTextureBlendMode( mTexture, blending );
void LTexture::setAlpha( Uint8 alpha )
//Modulate texture alpha
SDL_SetTextureAlphaMod( mTexture, alpha );
void LTexture::render(SDL_Renderer *&gRenderer, int x, int y, SDL_Rect *clip, double angle, SDL_Point *center, SDL_RendererFlip flip)
//Set rendering space and render to screen
SDL_Rect renderQuad = x, y, mWidth, mHeight ;
if( clip != NULL )
renderQuad.w = clip->w;
renderQuad.h = clip->h;
SDL_RenderCopyEx( gRenderer, mTexture, clip, &renderQuad, angle, center, flip );
【问题讨论】：
【参考方案1】：问题在于 if 语句末尾的分号。
if( !gTextTexture.loadFromRenderedText(gFont, "Hello I am hot", textColor, gRenderer));
printf( "Failed to render text texture!\n" );
success = false;
该分号将为该 if 块创建一个空语句，它将导致您的
printf( "Failed to render text texture!\n" );
success = false;
始终执行。是这样的，
if(.....)
;
....
【讨论】：
如果返回 true，则输出“无法渲染文本纹理”。这就是它的作用，它不会返回 false。 天啊，我没看到！太感谢了！我知道那个 if 语句有问题，该死的，非常感谢！以上是关于SDL2 - 应该返回 True 的函数评估为 False的主要内容，如果未能解决你的问题，请参考以下文章
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