4 replies to this topic

[kaktusas2598]

Hello all I am refreshing my kwoledge on SDL, using Lazy foo tutorials, and I need to code all my projects for SDL in C. So I convert all his C++ code to C. Bet I have serious issue in 12th tutorial about timing. Here is my code:
[source lang="cpp"]#include "SDL/SDL.h"#include "SDL/SDL_image.h"#include "SDL/SDL_ttf.h"const int SCREEN_WIDTH = 640;const int SCREEN_HEIGHT = 480;const int SCREEN_BPP = 32;SDL_Surface* message = NULL;SDL_Surface* seconds = NULL;SDL_Surface *background = NULL;SDL_Surface *screen = NULL;SDL_Event event;TTF_Font* font = NULL;SDL_Color textColor = {255,0,0};//white, same 0xff,0xff,0xffSDL_Surface *load_image( char *filename ){ SDL_Surface* loadedImage = NULL; SDL_Surface* optimizedImage = NULL; loadedImage = IMG_Load( filename ); if( loadedImage != NULL ) { optimizedImage = SDL_DisplayFormat( loadedImage ); SDL_FreeSurface( loadedImage ); if (optimizedImage != NULL) { //map the color key Uint32 colorkey = SDL_MapRGB(optimizedImage->format, 0,0xFF,0xFF); //sets all pixels of color R0, G 0xFF, B 0xFF to be tranparent SDL_SetColorKey(optimizedImage, SDL_SRCCOLORKEY, colorkey); } } return optimizedImage;}void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination ){ SDL_Rect offset; offset.x = x; offset.y = y; SDL_BlitSurface( source, NULL, destination, &offset );}int init(char * caption){ if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 ) { return 0; } screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE); if( screen == NULL ) { return 0; } //initiliaze SDL_ttf if (TTF_Init() == -1) { return 0; } SDL_WM_SetCaption( caption, NULL ); return 1;}int load_files(){ background = load_image("background.png"); //open the font font = TTF_OpenFont("lazy.ttf",30); if( background == NULL ) { return 0; } if( font == NULL ) { return 0; } return 1;}void clean_up(){ SDL_FreeSurface( background ); SDL_FreeSurface( message ); TTF_CloseFont(font); TTF_Quit(); SDL_Quit();}int main( int argc, char* args[] ){ int quit = 0;//make sure program waits for quit //the timer starting time Uint32 start = 0; //the timer start/stop flag int running = 0; if( init("Simple timer") == 0 )return 1; if(load_files() == 0) return 1; message = TTF_RenderText_Solid(font,"Press s to start/stop the timer", textColor); if (message == 0) return 1; //start the timer start = SDL_GetTicks(); //main loop while (!quit)//while user hasnt quit { //while there's event to handle! while(SDL_PollEvent(&event)) { //if user has Xed out if(event.type == SDL_QUIT) { //quit the program quit = 1; } else if(event.type == SDL_KEYDOWN) { if(event.key.keysym.sym == SDLK_s) { //if timer is running if(running) { //stop the timer running = 0; start = 0; } else { //start the timer running = 1; start = SDL_GetTicks(); } } else if(event.key.keysym.sym == SDLK_ESCAPE) { quit = 1; } } //rendering apply_surface(0,0,background,screen); apply_surface((SCREEN_WIDTH - message->w)/2,SCREEN_HEIGHT/2,message,screen); //if the timer is running if(running) { //timer: as a string char* time = "Timer: "; //current time as a string char* current = 0; //convert timers time to a string itoa((SDL_GetTicks() - start), current, 10); //adds time (Timer: ) + time in ms strcat(time, current); //renders the time surface seconds = TTF_RenderText_Solid(font, time, textColor); //apply the times surface apply_surface((SCREEN_WIDTH - seconds->w)/2,50,seconds,screen); SDL_FreeSurface(seconds); } //updating if( SDL_Flip( screen ) == -1 ) { return 1; } } } clean_up(); return 0;}[/source]
It doesn't have any compile or link errors, I can launch it, surfaces loads, but when I press 's'(to start/stop timer) it suddenly quits. I don't have idea what the problem might be, but I think issue in my "C version" of converting SDL time to string (Lazy Foo used string streams to handle this). This is the code where I used some standart C functions for doing so:
[source lang="cpp"]//rendering apply_surface(0,0,background,screen); apply_surface((SCREEN_WIDTH - message->w)/2,SCREEN_HEIGHT/2,message,screen); //if the timer is running if(running) { //timer: as a string char* time = "Timer: "; //current time as a string char* current = 0; //convert timers time to a string itoa((SDL_GetTicks() - start), current, 10); //adds time (Timer: ) + time in ms strcat(time, current); //renders the time surface seconds = TTF_RenderText_Solid(font, time, textColor); //apply the times surface apply_surface((SCREEN_WIDTH - seconds->w)/2,50,seconds,screen); SDL_FreeSurface(seconds); }[/source]

[ultramailman]

//timer: as a string
char* time = "Timer: ";
/*...*/
strcat(time, current);

The length of "time" is fixed at 7. You can't concatenate anything to it.

[Álvaro]

Besides what ultramailman said...

char* current = 0;
//convert timers time to a string
itoa((SDL_GetTicks() - start), current, 10);

I am not sure what the semantics of you itoa function are (itoa is not a standard function), but you typically have to pass a pointer to a buffer big enough to hold the answer. If you pass 0, you are asking for trouble.

You don't seem to have a grasp of how to handle strings in C. Try to read up on it, because it's not easy to teach you about it in a forum post.

Why don't you want to use C++ anyway? C++ provides much cleaner ways to handle this type of thing.

[BeerNutts]

Besides your C string issues, do you also realize your rendering code will only run while this is true: ?

while(SDL_PollEvent(&event))

since all the rendering is done within that loop (meaning, it only renders when it gets an event, typically an input event).

[kaktusas2598]

You are right guys, it was silly mistake, now it works, thanks for your assistance