Type Mismatch: Integer to Character

The function returns an unsigned char cast to an int, but the return value is assigned to a char type.

When an unsigned character cast to an integer is assign to a signed character, its value might be indistinguishable from EOF.

Example 1: The following code reads a character and compares it to EOF.

char c;

while ( (c = getchar()) != '\n' && c != EOF ) {
  ...
}

In this case, the return value from getchar() is cast to a char and compared to EOF (an int). Assuming c is a signed 8-bit value and EOF is a 32-bit signed value, then if getchar() returns a character represented by 0xFF, the value of c will be sign extended to 0xFFFFFFFF in the comparison to EOF. Since EOF is typically defined as -1 (0xFFFFFFFF), the loop will terminate erroneously.