SDL Wiki

SDL_AllocRW

Use this function to allocate an empty, unpopulated SDL_RWops structure.

Syntax

SDL_RWops* SDL_AllocRW(void);

Return Value

Returns a pointer to the allocated memory on success, or NULL on failure; call SDL_GetError() for more information.

Remarks

Applications do not need to use this function unless they are providing their own SDL_RWops implementation. If you just need a SDL_RWops to read/write a common data source, you should use the built-in implementations in SDL, like SDL_RWFromFile() or SDL_RWFromMem(), etc.

You must free the returned pointer with SDL_FreeRW(). Depending on your operating system and compiler, there may be a difference between the malloc() and free() your program uses and the versions SDL calls internally. Trying to mix the two can cause crashing such as segmentation faults. Since all SDL_RWops must free themselves when their close method is called, all SDL_RWops must be allocated through this function, so they can all be freed correctly with SDL_FreeRW().

Version

This function is available since SDL 2.0.0.

Code Examples

#include <stdlib.h>
#include "SDL.h"

/* These functions should not be used except from pointers in an SDL_RWops */
static Sint64 mysizefunc(SDL_RWops * context)
{
    return -1;
}

static Sint64 myseekfunc(SDL_RWops *context, Sint64 offset, int whence)
{
    return SDL_SetError("Can't seek in this kind of SDL_RWops");
}

static size_t myreadfunc(SDL_RWops *context, void *ptr, size_t size, size_t maxnum)
{
    SDL_memset(ptr,0,size*maxnum);
    return maxnum;
}

static size_t mywritefunc(SDL_RWops *context, const void *ptr, size_t size, size_t num)
{
    return num;
}

static int myclosefunc(SDL_RWops *context)
{
    if(context->type != 0xdeadbeef) {
        return SDL_SetError("Wrong kind of SDL_RWops for myclosefunc()");
    }

    free(context->hidden.unknown.data1);
    SDL_FreeRW(context);
    return 0;
}

SDL_RWops *MyCustomRWop(void)
{
    SDL_RWops *c=SDL_AllocRW();
    if(c==NULL) return NULL;

    c->size = mysizefunc;
    c->seek = myseekfunc;
    c->read = myreadfunc;
    c->write = mywritefunc;
    c->close = myclosefunc;
    c->type = 0xdeadbeef;
    c->hidden.unknown.data1 = SDL_malloc(256);
    return c;
}
SDL_FreeRW

CategoryAPI, CategoryIO


[ edit | delete | history | feedback | raw ]

[ front page | index | search | recent changes | git repo | offline html ]

All wiki content is licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).
Wiki powered by ghwikipp.