External Types Used is one of the source-code metrics Understand computes across 17+ languages — browse them in the GUI, export and track them, or script them with the Python API.
External Types Used
API ID: CountCFileExternalTypesUsedLanguages: C, C++
Targets: Files
For C/C++ files, the number of External Types Used.
This is approximately how many entities would appear in the Information Browser for that category.