Synopsis

A file opened as read-only is written to.

Enabled by default

Yes

Severity/Certainty

Medium/Medium

Full description

A file opened as read-only is written to. This will cause a runtime error in your application, either silently if the file exists, or as a crash if it does not exist. This check is identical to MISRAC2012-Rule-22.4.

Coding standards

Code examples

The following code example fails the check and will give a warning:

#include <stdio.h>
#include <stdlib.h>

void example(void) {
  FILE *f1;
  f1 = fopen("test-file.txt", "r");
  fprintf(f1, "Hello, World!");
  fclose(f1);
}

The following code example passes the check and will not give a warning about this issue:

#include <stdio.h>
#include <stdlib.h>

void example(void) {
  FILE *f1;
  f1 = fopen("test-file.txt", "r+");
  fprintf(f1, "Hello, World!");
  fclose(f1);
}