This may be a bit 'meta', but there's an example thats written in clang as a tool to run on clang (although, there's more to it than just that.
RemoveCStrCalls.cpp
// This file implements a tool that prints replacements that remove redundant
// calls of c_str() on strings.
//
// Usage:
// remove-cstr-calls ...
//
// Where is a CMake build directory in which a file named
// compile_commands.json exists (enable -DCMAKE_EXPORT_COMPILE_COMMANDS in
// CMake to get this output).
//
// ... specify the paths of files in the CMake source tree. This path
// is looked up in the compile command database. If the path of a file is
// absolute, it needs to point into CMake's source tree. If the path is
// relative, the current working directory needs to be in the CMake source
// tree and the file must be in a subdirectory of the current working
// directory. "./" prefixes in the relative files will be automatically
// removed, but the rest of a relative path must be a suffix of a path in
// the compile command line database.
//
// For example, to use remove-cstr-calls on all files in a subtree of the
// source tree, use:
//
// /path/in/subtree $ find . -name '*.cpp'|
// xargs remove-cstr-calls /path/to/source
