Cannot Use Printf!?! (while performing hashing algorithm using mhash) - c

Question

I am using Mhash and I would like to print the length of my blocksize for debugging purposes, but I keep getting an error every time I try to compile
Any suggestions on how I can fix this error?
Here is my code:
#include <mhash.h>
#include <stdio.h>
#include <string.h>
// 0x12e6bc6e68c3b9506e6668db6b7224f894fab073728fc179 (TIGER192) (48)
int main()
{
char password[] = "Jefe";
int keylen = 4;
char data[] = "what do ya want for nothing?";
int datalen = 28;
MHASH td, td2;
unsigned char *mac, *mac2;
int i, j;
td = mhash_hmac_init(MHASH_TIGER192, password, keylen, mhash_get_hash_pblock(MHASH_TIGER192));
mhash(td, data, datalen);
mac = mhash_hmac_end(td);
printf("0x");
for (i = 0; i < mhash_get_block_size(MHASH_TIGER192); i++)
{
printf("%.2x", mac[i]);
}
printf("\n");
// int length = strlen(mac);
// printf(length);
// int length = 5;
// printf(length);
exit(0);
}
I run the program with the following commands:
hb2#hb1:~/Desktop$ gcc -o hashexample hashexample.c -lmhash
hb2#hb1:~/Desktop$ ./hashexample
0x12e6bc6e68c3b9506e6668db6b7224f894fab073728fc179
And it runs successfully, but when I try to print the length of the hashed result, I get the following error!!? Any ideas on why?
// int length = strlen(mac);
// printf(length);
hb2#hb1:~/Desktop$ gcc -o hashexample hashexample.c -lmhash
hashexample.c: In function ‘main’:
hashexample.c:33:2: warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast [enabled by default]
/usr/include/stdio.h:363:12: note: expected ‘const char * __restrict__’ but argument is of type ‘int’
hashexample.c:33:2: warning: format not a string literal and no format arguments [-Wformat-security]
At first, I thought it was because I thought I was using strlen incorrectly?! But even when I try to do a simple printf of an integer, I still get an error:
// int length = 5;
// printf(length);
hb2#hb1:~/Desktop$ gcc -o hashexample hashexample.c -lmhash
hashexample.c: In function ‘main’:
hashexample.c:35:2: warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast [enabled by default]
/usr/include/stdio.h:363:12: note: expected ‘const char * __restrict__’ but argument is of type ‘int’
hashexample.c:35:2: warning: format not a string literal and no format arguments [-Wformat-security]
Thanks for your help in advance!

Answer 1

Check the man page for printf(). The first argument is a const char *. You're passing an int.
That's what the warning says too:
warning: passing argument 1 of ‘printf’ makes pointer from integer without a cast [enabled by default]
You wanted:
printf("%d", length);
You need the format string to specify that an int is going to be printed.