Thread: simple program to convert unsigned long to string throw segment fault

Code:

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

#define		HTTP_URI_FMT				"http://%s:%lu/%s"
#define IPCOMP(addr, n) ((addr >> (24 - 8 * n)) & 0xFF)
#define IP_ADDR_LEN 20
int main()
{
	unsigned long i= 19216811;
	static char UI8Ip[IP_ADDR_LEN];
	unsigned long port	= 80;
	char folder[] = "anoop/anoop";
	char buff[255];
	
snprintf((char *)UI8Ip, IP_ADDR_LEN, "%ld.%ld.%ld.%ld", IPCOMP(i, 3), IPCOMP(i, 2), IPCOMP(i, 1), IPCOMP(i, 0));

	//sprintf(buff,"http://%lu:%lu/%s",i,port,buff);
	snprintf(buff, 255, HTTP_URI_FMT, i, port, folder);


	printf("Val of:%s",buff);
	return 0;
}

I am struck with the segment fault

Regards,
Anoop

Originally Posted by sanddune008

Code:

    unsigned long i= 19216811;

Just to pick nits, but what IP address is equivalent to the decimal value 19216811? Answer: 1.37.57.171.

It looks like you tried to convert 192.168.1.1 to a decimal value by removing the dots; that's not going to work. One way to do it is to shift 192 left by 24 bits, shift 168 left by 16 bits, shift 1 left by 8 bits, shift 1 left by 0 bits, and then add them all up. Shifting left by N bits is the same as multiplying by 2^N.

192*2^24 + 168*2^16 + 1*2^8 + 1*2^0 = 3232235777

This is basically the opposite as extracting all four octets, as your code does with IPCOMP. You could even write a macro to convert four octets to an integer, which would make the conversion less error-prone.