Question

I use crypt() function and the compile flag named -lcrypt the problem is that the compiler says undefined reference to crypt(). Can anyone tell me what I’m doing wrong?

Makefile

    CC = gcc
    CFLAGS=-Wall -lm -lcrypt
    OBJS = get_passwords_hashed.o
    PROG = get_passwords_hashed.exe

    #adicionar or mudar o OBJS se tiver outras files para o programa


    #GENERIC

    all:    ${PROG}

    clean:
            rm ${OBJS} *~ ${PROG}

    ${PROG}: ${OBJS}
            ${CC} ${OBJS} -o $@

    .c.o:
            ${CC} $< -c -o $@
    # $@ - turns .c into .o 
    ###################################
    #dependencias
    so_final.o: get_passwords_hashed.c get_passwords_hashed.h

main.c

#include <stdio.h>
#include <string.h>
#include <crypt.h>

int testar_pass(char ant[],char (*pointer_hashes)[max_chars_string]){ // ponteiro para array de chars - char ** ant
     char * password ;
     char * encrypted;
     password = malloc(strlen(ant)*sizeof(char)); //password calculada recebida anteriror
     encrypted = malloc(strlen(ant)*sizeof(char));//hash
     strcpy(password,ant);
     encrypted = crypt(password,"10");
     if(strcmp(*pointer_hashes,encrypted) == 0){
         return 1;
         }
     else return 0;// devolve erro
}

Answer 1

Pass -lm -lcrypt at the end of your compilation line.

LIBS=-lm -lcrypt

${CC} ${OBJS} -o $@ ${LIBS}

EDIT:

The explanation of why it makes a difference (as requested in a comment) from gcc manual:

-llibrary

[…]

It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the
order they are specified.

Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file ‘foo.o’ but before ‘bar.o’. If ‘bar.o’ refers to functions in ‘z’, those functions
may not be loaded.