Update test_coverage_visualization.md

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doc/user/project/merge_requests/test_coverage_visualization.md

@@ -219,3 +219,32 @@ run tests:
     reports:
       cobertura: coverage.xml
 ```
+
+### C/C++ example
+
+The following [`gitlab-ci.yml`](../../../ci/yaml/README.md) example for C/C++ with
+`gcc` or `g++` as the compiler uses [`gcovr`](https://gcovr.com/en/stable/) to generate the coverage
+output file in Cobertura XML format.
+
+This example assumes:
+
+- That the `Makefile` is created by `cmake` in the `build` directory,
+  within another job in a previous stage.
+  (If you use `automake` to generate the `Makefile`,
+  then you need to call `make check` instead of `make test`.)
+- `cmake` (or `automake`) has set the compiler option `--coverage`.
+
+```yaml
+run tests:
+  stage: test
+  script:
+    - cd build
+    - make test
+    - gcovr --xml-pretty --exclude-unreachable-branches --print-summary -o coverage.xml --root ${CI_PROJECT_DIR}
+  coverage: /^\s*lines:\s*\d+.\d+\%/
+  artifacts:
+    name: ${CI_JOB_NAME}-${CI_COMMIT_REF_NAME}-${CI_COMMIT_SHA}
+    expire_in: 2 days
+    reports:
+      cobertura: build/coverage.xml
+```