utility of the day

gcov - coverage testing tool

        -:    0:Source:/tmp/1.c
        -:    0:Graph:1.gcno
        -:    0:Data:1.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:#include <stdio.h>
        -:    2:
        -:    3:void foo()
        1:    4:{
        1:    5:  printf("int:\t%ld\n", (long) sizeof(int));
        1:    6:  printf("long:\t%ld\n", (long) sizeof(long));
        1:    7:}
        -:    8:
        -:    9:void bar()
    #####:   10:{
    #####:   11:  printf("size_t:\t%ld\n", (long) sizeof(size_t));
    #####:   12:  printf("void*:\t%ld\n", (long) sizeof(void*));
    #####:   13:}
        -:   14:
        -:   15:int main()
        1:   16:{
        1:   17:  foo();
        -:   18:/*   bar(); */
        1:   19:  return 0;
        -:   20:}

The lines marked with `#####' were never executed.

Compile with `--coverage' and run yer program:

  $ vi /tmp/1.c
  $ cd /tmp
  $ gcc --coverage -g -Wall -W -o 1 1.c
  $ ./1 >/dev/null
  $ gcov /tmp/1.c
  File '/tmp/1.c'
  Lines executed:63.64% of 11
  /tmp/1.c:creating '1.c.gcov'

GCC only.

Update: gcov with `-b' option measures branch coverage.

See also:

• SQLite: A Lesson In Low-Defect Software blog post
• the presentation it mentions
• and the corresponding reddit discussion