C
Coverage
Learn code coverage measurement.
Coverage
Code coverage measures how much of the source code the tests exercise. The gcov and lcov tools ship with GCC; they give execution counts for each line and branch.
In this lesson we count branches manually with a coverage_counter; this is a simplified view of what gcov does behind the scenes. The sign(int n) function has three branches: positive, negative and zero. If a test exercises only one branch, coverage is 1/3.
Counting branches
You declare a coverage_counter global variable. The sign function increments the counter in each branch; you see which branches ran. Test coverage is the ratio of executed branches to total branches.
Example: int sign(int n) { if (n > 0) { coverage_counter++; return 1; } if (n < 0) { coverage_counter++; return -1; } coverage_counter++; return 0; }. Calling sign(5) exercises only the first branch; the counter becomes 1. For full coverage you must test all three branches.
Exercise sign with coverage counter
Declare a global int coverage_counter = 0;. Write int sign(int n): if n > 0 do { coverage_counter++; return 1; }, if n < 0 do { coverage_counter++; return -1; }, else coverage_counter++; return 0;. In main compute int r = sign(5); and print printf("kapsam: %d\n", coverage_counter); and printf("sign: %d\n", r);.
Show example solution
#include <stdio.h>
int coverage_counter = 0;
int sign(int n) {
if (n > 0) { coverage_counter++; return 1; }
if (n < 0) { coverage_counter++; return -1; }
coverage_counter++;
return 0;
}
int main(void) {
int r = sign(5);
printf("kapsam: %d\n", coverage_counter);
printf("sign: %d\n", r);
return 0;
}
Test yourself
-
What does gcov measure?
- Memory usage
- Code coverage
- File size
- CPU speed
Show answer
Code coverage — gcov gives execution counts for each line and branch.
-
Match coverage tools
- gcov
- Line counter
- lcov
- HTML report
- sign
- Three-branch fn
- coverage_counter
- Manual counter
-
sign positive branch
if (n > 0) { coverage_counter++; return ____; }
Show answer
if (n > 0) { coverage_counter++; return 1; }
Next lesson: Test patterns
