test_append.c

#include<stdio.h>
#include<unistd.h>
int main (int argc, char *argv[])
{
   FILE *fp;
   char test_buf[30];

   fp = fopen("sdltest", "wb+");
   if (!fp) {
     printf("Could not open file\n");
     return 0;
   }

   if (fwrite("1234567890", 10, 1, fp) != 1) {
     printf("Could not write to file\n");
     goto error;
   }

   fclose(fp);
   fp = fopen("sdltest", "ab+");
   
   if (!fp) {
     printf("Could not open file\n");
     return 0;
   }

   if (fwrite("1234567890", 10, 1, fp) != 1) {
     printf("Could not write to file\n");
     goto error;
   }

   fseek(fp, 0, SEEK_SET);
   fread(test_buf, 20, 1, fp);
   printf("Read %s\n", test_buf);

   fseek(fp, -7, SEEK_END);
   long len = ftell(fp);
   if (len != 13) {
     printf("Could not seek correctly\n");
     printf("[DEBUG] len == %lu\n", len);
     goto error;
   }

 error:
   fclose(fp);
   unlink("sdltest");
   return 0;
}