clang -O2 -Wall -Wextra -Werror=implicit-function-declaration libintl/dcgettext_l.c -o libintl/dcgettext_l -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lintl libintl/dcgettext_l.c:19:17: error: implicit declaration of function 'dcgettext_l' is invalid in C99 [-Werror,-Wimplicit-function-declaration] char* output = dcgettext_l("os-test", input, LC_NUMERIC, locale); ^ libintl/dcgettext_l.c:19:17: note: did you mean 'dcgettext'? /usr/include/libintl.h:56:7: note: 'dcgettext' declared here char *dcgettext(const char *, const char *, int) __format_arg(2); ^ libintl/dcgettext_l.c:19:8: warning: incompatible integer to pointer conversion initializing 'char *' with an expression of type 'int' [-Wint-conversion] char* output = dcgettext_l("os-test", input, LC_NUMERIC, locale); ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1 warning and 1 error generated.