crypt function and link error “undefined reference to 'crypt'”

Question

I have used the crypt function in c to encrypt the given string. I have written the following code,

#include<stdio.h>
#include<unistd.h>

int main()
{
    printf("%s\n",crypt("passwd",1000));
}

But the above code threw an error ,"undefined reference to `crypt'". What is the problem in the above code.

Thanks in advance.

Answer 1

If you want to use the crypt() function, you need to link to the library that supplies it. Add -lcrypt to your compile command.

Older versions of glibc supplied a libcrypt library for this purpose, and declared the function in <unistd.h> - to compile against this support, you may also need to define either _XOPEN_SOURCE or _GNU_SOURCE in your code before including <unistd.h>.

Newer versions of glibc don't supply libcrypt - it is instead provided by a separate libxcrypt. You still link with -lcrypt, but the function is instead declared in <crypt.h>.

Answer 2

crypt() uses DES which is extremely insecure and probably older than you 12 years older than you.

I suggest you use a serious encryption algorithm, such as AES. Many libraries offer such encryption; OpenSSL (crypto.lib) is a good choice for example.

^{Not answering your actual question since a lot of people already did}

Answer 3

You need to include crypt.h if you want to use crypt(). Below your other two includes, add:

#include <crypt.h>

Answer 4

You need to put the following line before your includes:

#define _XOPEN_SOURCE

Answer 5

You have to #define __XOPEN_SOURCE before you #include the header files.

Answer 6

The crypt function is non-standard, but is supplied as an extension by the GNU C library on Linux. It's defined in <crypt.h>