GCDa

gcda is the file extension used by GCC's gcov coverage tooling for storing runtime coverage data. It accompanies the corresponding .gcno file, which describes the program’s control-flow graph, and together they enable generation of coverage reports.

When a program is compiled with coverage options, such as -fprofile-arcs -ftest-coverage or the modern -coverage, the compiler produces a .gcno file for each source file. During program execution, gcov writes or updates a .gcda file for each source file, recording how many times instrumented lines and branches were executed in that run. The .gcda files are binary data files located in the same directory as the source and its .gcno counterpart.

gcov uses both the .gcno and .gcda files to compute coverage statistics and to generate human-readable reports (for example, the textual .gcov reports or HTML reports via front-ends like lcov/genhtml). The data in a .gcda file can be accumulated across multiple runs, enabling aggregated coverage across tests, although users typically reset counters by removing older .gcda and .gcno files before re-running tests to obtain fresh results.

In summary, gcda files are the runtime coverage data produced by instrumented programs, essential for enabling code coverage analysis with gcov and related tools. They are not source code and are not intended to be edited manually; their primary purpose is to record execution counts to support coverage reporting.