Thread: STRTOK SegFaults!

Ok, now, I wouldnt normally do this, but I dont understand why this isnt working. Now, I know my getmask() function does practically nothing, but it serves its purpose for now. What my real problem is, is that when I try to strtok cSM, it seg faults. This is the EXACT SAME THING I am doing above with cIP, only difference is I'm taking the value from argv (which, I'm also going to add, when I change where Im getting cIP from (from argv to simple cIP="192.168.0.1") it crashes there too!). So my problem is, why the hell is strtok crashing? It's a char* filetype, so there shouldnt be ANY problems.

HELP!!!

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>

char* getmask(int nCIDR);

int main(int argc, char* argv[])
{
	int i;
	int nCIDR;
	int anIP[3];
	int anSubMask[3];
	char* cIP;
	char* cSM;
	char* ctemp;
	int ntemp;
	
		/*Make sure all arguments are there*/
	if (argc!= 3)
	{
		printf("Invalid number of arguments inputted.\nPlease run program again.\nEnding program\n");
		exit(1);
	}
	else
	{
			/*Copies in CIDR*/
		nCIDR=atoi(argv[2]);
			/*Copies in IP as CHAR*/
		cIP=argv[1];
						
		printf("IP: %s\nCIDR: %d\n", cIP, nCIDR);
			/*Checks to see if CIDR is correct*/
		if (nCIDR<0 || nCIDR>32)
		{
			printf("Please use a proper CIDR\nEnding program\n");
			exit(1);
		}
	}
		/*Convert IP to INT's*/
	anIP[0]=atoi(strtok(cIP, "."));
		/*Loop through and get rest of IP*/
	for(i=1; i!=4; i++)
		anIP[i]=atoi(strtok(NULL, "."));
	printf("The four parts of the IP address is...\n1: %d\n2: %d\n3: %d\n4: %d\n",anIP[0],anIP[1],anIP[2],anIP[3]);

		/*Get the Subnet Mask*/	
	cSM=getmask(nCIDR);
	
	printf("Toking up with SubMask: %s\n", cSM);
	ctemp=strtok(cSM,".");
	printf("Stoned!");
	anSubMask[0]=atoi(ctemp);
	printf("BAM!\n");
	
		/*Loop through and get rest of IP*/
	/*for(i=1; i!=4; i++)
		anSubMask[i]=atoi(strtok(NULL, "."));
	printf("The four parts of the IP address is...\n1: %d\n2: %d\n3: %d\n4: %d\n",naIP[0],naIP[1],naIP[2],naIP[3]);
	
	
	printf("The four parts of the SubNet Mask is...\n1: %d\n2: %d\n3: %d\n4: %d\n",anSubMask[0],anSubMask[1],anSubMask[2],anSubMask[3]);
	*/
	return(0);
}

char* getmask(int nCIDR)
{
	char* cMask;
	cMask="255.255.255.0";	
	return(cMask);
}

Originally Posted by Narf

cSM is set to a string literal. strtok modifies the string you pass to it, and you can't safely modify a string literal because it could be in read-only memory.

So what data type can I use for cSM to make STRTOK accept it? And why would it accept cIP no problem when they are clearly of the same type?