Synopsis

Do not call getc(), putc(), getwc(), or putwc() with a stream argument that has side effects.

Enabled by default

Yes

Severity/Certainty

Low/Low

Full description

Do not invoke getc() or putc() or their wide-character analogues getwc() and putwc() with a stream argument that has side effects. The stream argument passed to these macros may be evaluated more than once if these functions are implemented as unsafe macros.

Coding standards

Code examples

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

#include <stdio.h>

void func(const char *file_name) {
  FILE *fptr;

  int c = getc(fptr = fopen(file_name, "r"));
  if (feof(stdin) || ferror(stdin)) {
    /* Handle error */
  }

  if (fclose(fptr) == EOF) {
    /* Handle error */
  }
}

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

#include <stdio.h>

void func(const char *file_name) {
  int c;
  FILE *fptr;

  fptr = fopen(file_name, "r");
  if (fptr == NULL) {
    /* Handle error */
  }

  c = getc(fptr);
  if (c == EOF) {
    /* Handle error */
  }

  if (fclose(fptr) == EOF) {
    /* Handle error */
  }
}