get rid of unused return value from write callback

stb_image_write.h

 /* stb_image_write - v1.00 - public domain - http://nothings.org/stb/stb_image_write.h
-   writes out PNG/BMP/TGA images to C stdio - Sean Barrett 2010
+   writes out PNG/BMP/TGA images to C stdio - Sean Barrett 2010-2015
                                      no warranty implied; use at your own risk
 
    Before #including,
@@ -44,6 +44,9 @@ USAGE:
      int stbi_write_tga_to_func(stbi_write_func *func, void *context, int w, int h, int comp, const void  *data);
      int stbi_write_hdr_to_func(stbi_write_func *func, void *context, int w, int h, int comp, const float *data);
 
+   where the callback is:
+      void stbi_write_func(void *context, void *data, int size);
+
    You can define STBI_WRITE_NO_STDIO to disable the file variant of these
    functions, so the library will not use stdio.h at all. However, this will
    also disable HDR writing, because it requires stdio for formatted output.
@@ -125,7 +128,7 @@ STBIWDEF int stbi_write_tga(char const *filename, int w, int h, int comp, const
 STBIWDEF int stbi_write_hdr(char const *filename, int w, int h, int comp, const float *data);
 #endif
 
-typedef int stbi_write_func(void *context, void *data, int size);
+typedef void stbi_write_func(void *context, void *data, int size);
 
 STBIWDEF int stbi_write_png_to_func(stbi_write_func *func, void *context, int w, int h, int comp, const void  *data, int stride_in_bytes);
 STBIWDEF int stbi_write_bmp_to_func(stbi_write_func *func, void *context, int w, int h, int comp, const void  *data);
@@ -192,15 +195,15 @@ static void stbi__start_write_callbacks(stbi__write_context *s, stbi_write_func
 
 #ifndef STBI_WRITE_NO_STDIO
 
-static int stbi__stdio_write(void *user, void *data, int size)
+static void stbi__stdio_write(void *context, void *data, int size)
 {
-   return (int) fwrite(data,1,size,(FILE*) user);
+   fwrite(data,1,size,(FILE*) context);
 }
 
 static int stbi__start_write_file(stbi__write_context *s, const char *filename)
 {
    FILE *f = fopen(filename, "wb");
-   stbi__start_write_callbacks(s, &stbi__stdio_write, (void *) f);
+   stbi__start_write_callbacks(s, stbi__stdio_write, (void *) f);
    return f != NULL;
 }
 

tests/image_test.c

@@ -53,7 +53,7 @@ void test_ycbcr(void)
 
 float hdr_data[200][200][3];
 
-void dummy(void *context, void *data, int len)
+void dummy_write(void *context, void *data, int len)
 {
    static char dummy[1024];
    if (len > 1024) len = 1024;
@@ -97,6 +97,9 @@ int main(int argc, char **argv)
             stbi_write_png(stb_sprintf("output/%s.png", fname), w, h, 4, data, w*4);
             stbi_write_bmp(stb_sprintf("output/%s.bmp", fname), w, h, 4, data);
             stbi_write_tga(stb_sprintf("output/%s.tga", fname), w, h, 4, data);
+            stbi_write_png_to_func(dummy_write,0, w, h, 4, data, w*4);
+            stbi_write_bmp_to_func(dummy_write,0, w, h, 4, data);
+            stbi_write_tga_to_func(dummy_write,0, w, h, 4, data);
             free(data);
          } else
             printf("FAILED 4\n");