Gcov is a tool you can use in conjunction with GCC to test code coverage in your programs. This extension visualizes the output of gcov in Visual Studio Code. It allows you to see which lines of the program have been executed and how often.
Compile your code with gcc/g++ (version >= 9) with --coverage and without optimizations.
Run your program or tests.
Open a source file in vscode and use ctrl+shift+P to run the Gcov Viewer: Show command.
During compilation, gcc will generate a .gcno file next to every .o file. When you run the program, it will create .gcda files in the same location. Those contain information about how often functions and lines have been executed.
This vscode extension uses the gcov program to parse these additional files and displays the information on top of your source files. For this to work, it has to find the generated .gcda for a given project. Those are usually in your build directory. If the extension does not find them on its own, you have to edit the gcovViewer.buildDirectories setting of your workspace folder. The most convenient way to do this is to use the Gcov Viewer: Select Build Directory command.
Sometimes lines are counted more than once when they do more than one thing. That might be confusing in some cases. Usually it is quite easy to get the correct number by looking at neighboring lines.
When the Highlight Missed Lines setting is enabled, some missed lines might not be marked as such.
Only works with version 9 or higher of gcc, g++ and gcov. If you have multiple versions of gcov, you might have to change the Gcov Binary setting.