CWARN.CMPCHR.EOF

Char expression is compared with EOF constant

The CWARN.CMPCHR.EOF checker flags instances in which a char expression is compared with an EOF constant.

Vulnerability and risk

Functions for reading single characters from a file, such as getchar, fgetc and getc, normally return an int value to distinguish an EOF return value (0xffffffff on 32-bit platforms) from a read byte whose value equals -1 (0x000000ff). So it's typically a mistake when a variable of char type is compared with an EOF constant, and an int variable should be used instead.

Vulnerable code example

Copy 
 #include <stdio.h>
 
 void read_file(FILE *file) {
   char c;
   do {
     c = fgetc(file);
   } while(c != EOF);
 }

Klocwork flags the attempt to compare char variable 'c' to the EOF return variable at line 6.

Fixed code example

Copy 
 #include <stdio.h>
 
 void read_file(FILE *file) {
   int c;    
   do {
     c = fgetc(file);
   } while(c != EOF);
 }

In the fixed example, variable 'c' is correctly defined as an int type.

External guidance