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This code calls the getc() function with an expression as an argument. If getc() is implemented as a macro, the file may be opened several times (see FIO31-C. Do not simultaneously open the same file multiple times).

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const char *filename = "test.txt";
FILE *fptr;

int c = getc(fptr = fopen(filenamefile_name, "r"));

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

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In this compliant solution, getc() is no longer called with an expression as its argument.

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const char *filename = "test.txt";
FILE *fptr = fopen(filenamefile_name, "r");
if (fptr == NULL) {
  /* Handle Error */
}

int c = getc(fptr);

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In this non-compliant example, putc() is called with c++ as an argument. If putc() is implemented as a macro, c++ could be evaluated several times within the macro expansion of putc() with unintended results.

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const char *filename = "test.txt";
FILE *fptr = fopen(filenamefile_name, "w");
if (fptr == NULL) {
  /* Handle Error */
}

int c = 'a';

while (c <= 'z') {
  putc(c++, fptr);
}

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In the compliant solution, c++ is no longer an argument to putc().

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const char *filename = "test.txt";
FILE *fptr = fopen(filenamefile_name, "w");
if (fptr == NULL) {
  /* Handle Error */
}

int c = 'a';

while (c <= 'z') {
  putc(c, fptr);
  c++;
}

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