gcc -pthread -Wall -Wextra -Werror=implicit-function-declaration unistd/encrypt.c -o unistd/encrypt -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt -lxnet -lsocket -latomic unistd/encrypt.c: In function 'main': unistd/encrypt.c:19:9: error: implicit declaration of function 'encrypt' [-Wimplicit-function-declaration] 19 | encrypt(buffer, 0); | ^~~~~~~