cc -pthread -Wall -Wextra -Werror=implicit-function-declaration wctype/wctrans_l.c -o wctype/wctrans_l -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -liconv wctype/wctrans_l.c:13:19: error: call to undeclared function 'wctrans_l'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration] 13 | wctrans_t desc = wctrans_l("tolower", locale); | ^ wctype/wctrans_l.c:13:19: note: did you mean 'wctrans'? /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_wctype.h:126:2: note: 'wctrans' declared here 126 | wctrans(const char *); | ^ 1 error generated.