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Use this function to read from a data source.


size_t SDL_RWread(struct SDL_RWops* context,
                  void*             ptr,
                  size_t            size,
                  size_t            maxnum)

Function Parameters


a pointer to an SDL_RWops structure


a pointer to a buffer to read data into


the size of each object to read, in bytes


the maximum number of objects to be read

Return Value

Returns the number of objects read, or 0 at error or end of file; call SDL_GetError() for more information.

Code Examples

SDL_RWops *rw = SDL_RWFromFile("test.bin","r");
if (rw != NULL) {
    extern Uint8 buf[256];
    SDL_RWread(rw, buf, sizeof (buf), 1);

Read a complete file in memory (assuming size can be detected) (from OpenGL WikiBook):

char* file_read(const char* filename) {
        SDL_RWops *rw = SDL_RWFromFile(filename, "rb");
        if (rw == NULL) return NULL;

        Sint64 res_size = SDL_RWsize(rw);
        char* res = (char*)malloc(res_size + 1);

        Sint64 nb_read_total = 0, nb_read = 1;
        char* buf = res;
        while (nb_read_total < res_size && nb_read != 0) {
                nb_read = SDL_RWread(rw, buf, 1, (res_size - nb_read_total));
                nb_read_total += nb_read;
                buf += nb_read;
        if (nb_read_total != res_size) {
                return NULL;

        res[nb_read_total] = '\0';
        return res;


This function reads up to maxnum objects each of size size from the data source to the area pointed at by ptr. This function may read less objects than requested. It will return zero when there has been an error or the data stream is completely read.

SDL_RWread() is actually a macro that calls the SDL_RWops's read method appropriately, to simplify application development.

More Examples

Uint32 buffer[10];
SDL_RWread(rwop, buffer, sizeof(Uint32), 10);

This will read 40 bytes of data, and put it into 'buffer', which is intended to hold 32-bit integers. Each Uint32 is 4 bytes, or 32-bits.

Uint64 buffer[10];
SDL_RWread(rwop, buffer, sizeof(Uint64), 10);

This will read 80 bytes of data, and place them into 'buffer', which is now designed for 64-bit integers (Uint64 values). Each Uint64 (long) is 8 bytes, and we are reading 10 of them (as shown by buffer[10] when we make it).

CategoryAPI, CategoryIO

None: SDL_RWread (last edited 2015-09-17 21:55:16 by PhilippWiesemann)

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