Thread: Segmentation fault

Hello,
I need a little help.
This code works without any errors.

Code:

int main()
{
	int i=0;
        char c=0;
	char *command;

	while ((c=getchar()) != '\n'){  
	    command[i]=c;
	    i++;
	 }

	command[i]='\0';
	return 1;
}

However, when I add a new variable, for example:

int main()
{
	int i=0, k=0;
        char c=0;
	char *command;

	while ((c=getchar()) != '\n'){  
	    command[i]=c;
	    i++;
	 }

	command[i]='\0';
	printf(" k is %d\n", k+3);[/B]
	return 1;
}

the codes stop working and I get a "Segmentation fault" announcement.
What is the problem?

Thanks

Well, in both cases, command is a pointer to char that does not point to anything in particular, yet you write command[i] = c;

Incidentally, c should be an int instead of a char since getchar() returns an int (as is necessary to compare with EOF, should you choose to do so).

Oh, and please post code in [code][/code] bbcode tags.

I've change c type to int, but I still got segmentation fault (and I'v change to compare with EOF)

And moreover, it stopped working without the new variable.

Yeah, but that does not address the first part: command does not point to anything. Change it to be an array instead, then check that i is always a valid index before you do command[i].

> char *command;
Where does this point?

You've written
char *command = somerandomaddressinmemory;

Rearrange the code, you're walking in a different part of the mine-field.
The failure to blow up doesn't make it any less of a minefield.

Originally Posted by ksusha

The problem is that my input is of unknown length, and that's why I can't use an array

In that case, use malloc(), realloc() and free(). You would keep track of both the current size of the dynamic array (as in the number of elements in use) and its capacity. The former is already done with i, so you need another variable for the latter. When the size is about to exceed capacity, you "expand" the dynamic array with realloc().