Using Filters

Gcovr tries to only report coverage for files within your project, not for your libraries. This is influenced by the following options:

• -r, --root
• -f, --filter
• -e, --exclude
• --gcov-filter
• --gcov-exclude
• --exclude-directories
• (the current working directory where gcovr is invoked)

These options take filters. A filter is a regular expression that matches a file path. Because filters are regexes, you will have to escape “special” characters with a backslash \.

Always use forward slashes / as path separators, even on Windows:

• wrong: --filter C:\project\src\
• correct: --filter C:/project/src/

If the filter looks like an absolute path, it is matched against an absolute path. Otherwise, the filter is matched against a relative path, where that path is relative to the current directory or if defined in a configuration file to the directory of the file.

Examples of relative filters:

• --filter subdir/ matches only that subdirectory
• --filter '\.\./src/' matches a sibling directory ../src. But because a dot . matches any character in a regex, we have to escape it. You have to use additional shell escaping. This example uses single quotes for Bash or POSIX shell.
• --filter '(.+/)?foo\.c$' matches only files called foo.c. The regex must match from the start of the relative path, so we ignore any leading directory parts with (.+/)?. The $ at the end ensures that the path ends here.

If no -f/--filter is provided, the -r/--root is turned into a default filter. Therefore, files outside of the -r/--root directory are excluded.

To be included in a report, the source file must match any -f/--filter, and must not match any -e/--exclude filter.

The --gcov-filter and --gcov-exclude filters apply to the .gcov files created by gcov. This is useful mostly when running gcov yourself, and then invoking gcovr with -g/--use-gcov-files. But these filters also apply when gcov is launched by gcovr.

Speeding up coverage data search

The --exclude-directories filter is used while searching for raw coverage data (or for existing .gcov files when -g/--use-gcov-files is active). This filter is matched against directory paths, not file paths. If a directory matches, all its contents (files and subdirectories) will be excluded from the search. For example, consider this build directory:

build/
├─ main.o
├─ main.gcda
├─ main.gcno
├─ a/
│  ├─ awesome_code.o
│  ├─ awesome_code.gcda
│  └─ awesome_code.gcno
└─ b/
   ├─ better_code.o
   ├─ better_code.gcda
   └─ better_code.gcno

If we run gcovr --exclude-directories 'build/a$', this will exclude anything in the build/a directory but will use the coverage data for better_code.o and main.o.

This can speed up gcovr when you have a complicated build directory structure. Consider also using the search_paths or --object-directory arguments to specify where gcovr starts searching. If you are unsure which directories are being searched, run gcovr in -v/--verbose mode.

For each found coverage data file gcovr will invoke the gcov tool. This is typically the slowest part, and other filters can only be applied after this step. In some cases, parallel execution with the -j option might be helpful to speed up processing.

Filters for symlinks

Gcovr matches filters against real paths that have all their symlinks resolved. E.g. consider this project layout:

/home/you/
├─ project/  (pwd)
│  ├─ src/
│  ├─ relevant-library/ -> ../external-library/
│  └─ ignore-this/
└─ external-library/
   └─ src/

Here, the relevant-library has the real path /home/you/external-library.

To write a filter that includes both src/ and relevant-library/src/, we cannot use --filter relevant-library/src/ because that contains a symlink. Instead, we have to use an absolute path to the real name:

gcovr --filter src/ --filter /home/you/external-library/src/

or a relative path to the real path:

gcovr --filter src/ --filter '\.\./external-library/src/'

New in version 5.1: gcovr also supports symlinks/junctions/drive substitutions on Windows.