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FILE *fptr;

int c = getc(fptr = fopen(file_name, "r"));
if (c == EOF) {
  /* Handle Error */
}

This non-compliant code example also violaties FIO33-C. Detect and handle input output errors resulting in undefined behavior.

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FILE *fptr;
int c;

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

intif ((c = getc(fptr);)) == EOF) {
  /* Handle Error */
}

Non-Compliant Code Example: putc()

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FILE *fptr = NULL;
int c = 'a';
while (c <= 'z') {
  putc(c++, fptr ? fptr : (fptr = fopen(file_name, "w"));
}

If the putc() macro does evaluate evaluates its stream argument 2 or more multiple times, this might still seem safe, as the ?: operator ostensibly prevents multiple calls to fopen(). However, there is no guarantee that these would happen in distinct sequence points. So Consequently this coode might code also violate violates EXP30-C. Do not depend on order of evaluation between sequence points.

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FILE *fptr = fopen(file_name, "w");

if (fptr == NULL) {
  /* Handle Error */
}

int c = 'a';

while (c <= 'z') {
  if (putc(c++, fptr); == EOF) {
    /* Handle Error */
  }
}

The c++ is perfectly safe, since because putc() guarantees to evaluate its character argument exactly once.

This example only illustrates the side-effect issue.   The output will differ differs depending on the character set.

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