SDL_AllocRW
Name
SDL_AllocRW -- Allocates an empty, unpopulated SDL_RWops structure.
Synopsis
1 #include "SDL_rwops.h"
2
3 SDL_RWops *SDL_AllocRW(void);
Description
SDL_AllocRW allocates an empty, unpopulated SDL_RWops structure. You must fill out the fields yourself.
Return Value
Returns a pointer to the allocated memory on success, or NULL on error.
Note: You must free any memory allocated with SDL_AllocRW 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.
Example
1 #include <string.h> /* for memset */
2 #include "SDL_error.h" /* for SDL_SetError */
3 #include "SDL_rwops.h"
4
5 /* These functions should not be used except from pointers in a RWops */
6 static int myseekfunc(SDL_RWops *context, int offset, int whence)
7 {
8 SDL_SetError("Can't seek in this kind of RWops");
9 return(-1);
10 }
11
12 static int myreadfunc(SDL_RWops *context, void *ptr, int size, int maxnum)
13 {
14 memset(ptr,0,size*maxnum);
15 return(maxnum);
16 }
17
18 static int mywritefunc(SDL_RWops *context, const void *ptr, int size, int num)
19 {
20 return(num);
21 }
22
23 static int myclosefunc(SDL_RWops *context)
24 {
25 if(context->type != 0xdeadbeef)
26 {
27 SDL_SetError("Wrong kind of RWops for myclosefunc()");
28 return(-1);
29 }
30
31 free(context->hidden.unknown.data1);
32 SDL_FreeRW(context);
33 return(0);
34 }
35
36 /* Note that this function is NOT static -- we want it directly callable from other source files */
37 SDL_RWops *MyCustomRWop()
38 {
39 SDL_RWops *c=SDL_AllocRW();
40 if(c==NULL) return(NULL);
41
42 c->seek =myseekfunc;
43 c->read =myreadfunc;
44 c->write=mywritefunc;
45 c->close=myclosefunc;
46 c->type =0xdeadbeef;
47 c->hidden.unknown.data1=malloc(256);
48 return(c);
49 }