using openssl to calculate sha1 hash in linux

http://buttom-meal.blogspot.com/2009/04/linux-c-openssl-sha1.html
http://www.ibm.com/developerworks/linux/library/l-openssl.html

On centos 5
yum install openssl, openssl-devel

/*
Code snippet to calculate SHA1sum using openssl libs.
Copyright 2005 Junichi Uekawa, given to public domain.

$ gcc openssltest.c -lssl
$ ./a.out < ./a.out
eae8189278303caaa78f2d89e6a6ebeb7d37b554
$ sha1sum ./a.out
eae8189278303caaa78f2d89e6a6ebeb7d37b554 ./a.out
*/

#include "openssl/ssl.h"

main ()
{
SHA_CTX s;
int i, size;
char c[512];
unsigned char hash[20];

SHA1_Init(&s);
while ((size=read (0, c, 512)) > 0)
SHA1_Update(&s, c, size);
SHA1_Final(hash, &s);

for (i=0; i < 20; i++)
printf ("%.2x", (int)hash[i]);
printf ("\n");
}