cc -pthread -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations signal/sig2str.c -o signal/sig2str -D_POSIX_C_SOURCE=202405L -lm -lpthread -liconv signal/sig2str.c:5:27: error: use of undeclared identifier 'sig2str'; did you mean 'sigset'? int (*foo)(int, char *) = sig2str; ^~~~~~~ sigset /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/signal.h:99:22: note: 'sigset' declared here void (* _Nullable sigset(int, void (* _Nullable)(int)))(int); ^ signal/sig2str.c:5:7: error: incompatible function pointer types initializing 'int (*)(int, char *)' with an expression of type 'void (* _Nullable (int, void (* _Nullable)(int)))(int)' [-Werror,-Wincompatible-function-pointer-types] int (*foo)(int, char *) = sig2str; ^ ~~~~~~~ 2 errors generated.