Using gcov/lcov to generate code coverage statistics

This document describes how to write a test coverage with GCOV and LCOV. LCOV is a graphical front-end for GCC's coverage testing tool gcov. It collects gcov data for multiple source files and creates HTML pages containing the source code annotated with coverage information. It also adds overview pages for easy navigation within the file structure. LCOV supports statement, function and branch coverage measurement.

• HTML based output: coverage rates are additionally indicated using bar graphs and specific colors.

• Support for large projects: overview pages allow quick browsing of coverage data by providing three levels of detail: directory view, file view and source code view.

Getting started

TAOS-CI provides the automated code coverage tool by default. You just have to append the below statement in /etc/crontab file as following:

$ sudo vi /etc/crontab
#  30 * * * * www-data /var/www/html/{YOUR_REPO_NAME}/ci/gcov/coverage-generator.sh

In order to check the generated result, please run the below statement.

$ firefox /var/www/html/{YOUR_REPO_NAME}/ci/gcov_html/index.html

Advanced

Install required packages

$ apt install lcov

Write a cpp example code

$ vi menu.cpp

#include <iostream>
using namespace std;

void showChoices();
float add(float, float);
float subtract(float, float);
float multiply(float, float);
float divide(float, float);

int main()
{
           float x, y;
           int choice;
           do
           {
                       showChoices();
                       cin >> choice;
                       switch (choice)
                       {
                       case 1:
                                   cout << "Enter two numbers: ";
                                   cin >> x >> y;
                                   cout << "Sum " << add(x,y) <<endl;
                                   break;
                       case 2:
                                   cout << "Enter two numbers: ";
                                   cin >> x >> y;
                                   cout << "Difference " << subtract(x,y) <<endl;
                                   break;
                       case 3:
                                   cout << "Enter two numbers: ";
                                   cin >> x >> y;
                                   cout << "Product " << multiply(x,y) <<endl;
                                   break;
                       case 4:
                                   cout << "Enter two numbers: ";
                                   cin >> x >> y;
                                   cout << "Quotient " << divide(x,y) <<endl;
                                   break;
                       case 5:
                                   break;
                       default:
                                   cout << "Invalid input" << endl;
                       }
           }while (choice != 5);

           return 0;
}

void showChoices()
{
           cout << "MENU" << endl;
           cout << "1: Add " << endl;
           cout << "2: Subtract" << endl;
           cout << "3: Multiply " << endl;
           cout << "4: Divide " << endl;
           cout << "5: Exit " << endl;
           cout << "Enter your choice :";
}

float add(float a, float b)
{
           return a+b;
}

float subtract(float a, float b)
{
           return a-b;
}

float multiply(float a, float b)
{
           return a*b;
}

float divide(float a, float b)
{
           return a/b;
}

Generate .gcno using --coverage option

The –coverage option here is used to compile and link code needed for coverage analysis.

$g++ -o menu.out --coverage menu.cpp

Declare environment variable

Let's change the path that .gcda files are created. Next we need to export two variables namely GCOV_PREFIX and GCOV_PREFIX_STRIP. Set GCOV_PREFIX to the folder you want the output files to be in. The GCOV_PREFIX_STRIP is equal to the the number of forward slashes or “/” in the path.

$export GCOV_PREFIX="/home/taos-ci/public_html/{your_repo_name}/data"
$export GCOV_PREFIX_STRIP=5

Generate .gcda

You can generate .gcda file by running the example program.

$./menu.out

MENU
1: Add
2: Subtract
3: Multiply
4: Divide
5: Exit
Enter your choice :2
Enter two numbers: 3 4
Difference -1
MENU
1: Add
2: Subtract
3: Multiply
4: Divide
5: Exit
Enter your choice :5

Getting HTML output

Now, you can generate the report file with html format.

• lcov options:

  • -t: sets a test name
  • -o: to specify the output file
  • -c: to capture the coverage data
  • -d: to specify the directory where the data files needs to be searched

• genhtml option:

  • -o To specify the output folder name

$mv *.gcno ./data/
$cd data
$lcov -t "Code Coverate Statistics Report" -o lcov_app.info -c -d .
$genhtml -o html lcov_app.info

Run web-server with python module

Let's run a simple web-server with the "SimpleHTTPServer" module of Python.

$cd html 
$python -m "SimpleHTTPServer"         // To start a web-server with SimpleHTTPServer
$firefox  http://localhost/index.html 
$firefox  ./html/index.html           // To open the index.html directly

How to read the code coverage stats

• http://ltp.sourceforge.net/coverage/lcov/output/index.html

The red lines are the ones not executed or uncovered region. The blue lines are the ones covered. Also you can look at the Line data section for the number of times the lines have been executed.

Reference

• http://gcc.gnu.org/onlinedocs/gcc/Gcov.html
• http://ltp.sourceforge.net/coverage/lcov.php