Warn redefined macros by clang (-Wmacro-redefined)
Use -Wmacro-redefined flag to warn redefined macros by clang. #define MY_DEFINE 111 #define MY_DEFINE 222 int main(void) { return 0; } $ # M1 Mac (Ventura) + Apple clang 14.0.0 $ clang sample.cpp -Wmacro-redefined sample.cpp:2:9: warning: 'MY_DEFINE' macro redefined [-Wmacro-redefined] #define MY_DEFINE 222 ^ sample.cpp:1:9: note: previous definition is here #define MY_DEFINE 111 ^ 1 warning generated. The warnings are displayed automatically: clang enables -Wmacro-redefined by default.