giving function cast size

[nabeels786]

i have:

ipAddr=(char) inet_ntoa(ia);

//ipAddr = char ipAddr[15]

how can i cast the function so it's length = 15, and itll truncate the rest (maybe)

i tried this, doesnt work

ipAddr = (char [15]) inet_ntoa(ia);

thanks
-nabeel

[HarryW]

Well, first of all it's a string so you would cast it to char*, not char. Secondly, I have no idea how long the string this inet_ntoa() function might return can be, but I'll assume no more than 255 characters.

You need to make a buffer and copy the string the function returns into it. This is because although you could just get a pointer to the return string and keep using that, if the string that this function returns is declared at a scope local to the function you're calling, you will have stored a pointer to a string in memory that is not allocated and thus not protected from being altered by something outside your app while you're using it.

So anyway, once you've made a copy you can easily truncate the string to 15 characters by setting the 16th character to be a null-terminator, marking it as the end of the string. Anything after that in the array will get ignored by string functions.

So it looks something like this:

char ipAddr[256];
memset(ipAddr, 0, sizeof(char)); //clear out the string

strcpy(ipAddr, inet_ntoa(ia));  //copy into the buffer
ipAddr[15] = '\0';  //set 16th element to null-terminator

There is actually a more efficient and easier way of doing it if you know the returned string will be at least 15 characters long, and that's to just copy the first 15 characters (the first 15 bytes) of the string across using memcpy(), in which case you only need 16 characters allocated:

char ipAddr[16];
ipAddr[15] = '\0';  //set the null-terminator for the last character

memcpy(ipAddr, inet_ntoa(ia), 15);  //copy 15 chars into the buffer

[nabeels786]

yeah ive done that already, it seems to work so far. heres the whole function...any suggestions effeciency-wise?

u_long checkIP(const char *IP){
	char *ipAddr = new char[15];
	u_long iaIP;

	iaIP=inet_addr(IP);
	if (iaIP==INADDR_NONE) {

		HOSTENT* hst= new HOSTENT;
		hst = gethostbyname(IP);	

		struct in_addr ia; 

		// Resolve the hostname
		hst = gethostbyname(IP);	

		// Format it into a string.
		for(int i=0;hst->h_addr_list[i];i++){
			memcpy(&ia.s_addr,hst->h_addr_list[i],sizeof(ia.s_addr));
			ipAddr=(char *) inet_ntoa(ia);
		}

		printf ("Hostname %s resolved to %s",IP,ipAddr);
		iaIP = inet_addr(ipAddr);
		free (hst); //free memory used up
		
		//check whether its a 0 also
		if(iaIP == INADDR_NONE)
			return 0;
	}

	return iaIP;
}

[nabeels786]

alright it gives a pointer error after i try to access it

void main( int argc, char *argv[ ]) { 

	char *ipAddr = new char[15];
//	char hostName[255];
	int  hnLength=0;
	struct hostent *heHost=NULL;
	u_long  iaIP;	

	int startPort=0;
	int stopPort =0

	// get the ip address and stuff to use from 
	// the user
	printf("Please enter the IP Address to scan: ");
	scanf("%s",ipAddr);
	printf("Please enter the start port:");
	scanf("%i", &startPort);
	printf("Please enter the stop port: ");
	scanf("%i", &stopPort);

	if((iaIP=checkIP(ipAddr)) == 0){
		printf("An invalid IP Address was entered, exiting in one second...");
		Sleep(1000);
		return ;
	}
 ...
}

[nabeels786]

oh ok i got it to work, sorta.

i had to initialize winsock before i did that the calls.

thanks for the help

[HarryW]

It looks as if you may be unused to using dynamic memory allocation? In your second post you used the new operator to allocate some memory and then used the free() function to deallocate it when you'd finished with it. These are incompatible, you should use free() for memory allocated with malloc() and the delete (or delete[] for arrays) operator to deallocate memory allocated with new.

In the bit of code you posted most recently, you forgot to delete the array after you'd finished with it, too.

Apart from that, well done for getting it to work What are you writing? A ping app? Something to do reverse lookups?