Page History

...

These examples also assume that errno is set if fopen() or malloc() fail. These are guaranteed by POSIX but not by C11. See ERR30-C. Set errno to zero before calling a library function known to set errno, and check errno only after the function returns a value indicating failureTake care when reading errno for more details.

typedef struct object {  /* Generic struct: contents don't matter */
  int propertyA, propertyB, propertyC;
} object_t;

errno_t do_something(void){
  FILE *fin1, *fin2;
  object_t *obj;
  errno_t ret_val;
  
  fin1 = fopen("some_file", "r");
  if (fin1 == NULL) {
    return errno;
  }

  fin2 = fopen("some_other_file", "r");
  if (fin2 == NULL) {
    fclose(fin1);
    return errno;
  }

  obj = malloc(sizeof(object_t));
  if (obj == NULL) {
    ret_val = errno;
    fclose(fin1);
    return ret_val;  /* Forgot to close fin2!! */
  }

  /* ... More code ... */

  fclose(fin1);
  fclose(fin2);
  free(obj);
  return NOERR;
}

...

This method is beneficial because the code is cleaner, and the programmer does not need to rewrite similar code upon every function error.

Note that this guideline does not advocate more general uses of goto, which is still considered harmful. The use of goto in these cases is specifically to transfer control within a single function body.

Compliant Solution (copy_process() from Linux kernel)

...

...

Bibliography

...