Programming

#define _XOPEN_SOURCE
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <crypt.h>

int main (void)
{
    char *passwd;
    passwd = crypt("123456", "$1$yfKCUYj6");

}

gcc 1.c -o 1

/tmp/cci2MSHh.o: In function `main':
1.c:(.text+0x21): undefined reference to `crypt'
collect2: ld returned 1 exit status

SYNOPSIS
       #define _XOPEN_SOURCE
       #include <unistd.h>

       char *crypt(const char *key, const char *salt);

       char *crypt_r(const char *key, const char *salt,
                     struct crypt_data *data);

       Link with -lcrypt.

gcc -lcrypt 1.c -o 1