How can I initialize a string and then set it to the null terminator?

Question

I'm working on pset6. I'm at the part of the main.c function where I want to start combining the root and the absolute path. I was hoping to do something like this:

char* needle = NULL;
char* query = NULL;
needle = strchr(requestTarget, '?');
if (NULL == needle)
{
    query[0] = '\0';
}
else
{
    query = needle + 1;
}

The point here is to handle the case when there is no ? in the request path. I keep segmentation faulting when I try make that first if statement work, and there must be something about strings and char* and the like that I'm still not getting. When I do pass in things like /cat.jpg? HTTP/1.1 then it works fine -- my query has length 0.

Any hints would be appreciated!

Answer 1

The problem revolves around the var query.Remember first that it is a pointer, so it contains an address. Let's start with the else clause that works. If you find a ? in the string, you assign the address of the ? to needle, and then copy that address from needle to query and add 1 to that address.

The problem is in the 'then' clause of the if statement. At the point where you try to execute query[0] = '\0'; query is assigned the NULL pointer value - it doesn't point at anything. This statement tries to put something, \0, into a nonexistent memory location, causing the seg fault. Remember that query is just a pointer, not a string array.

For more info on char* x vs char array[size], etc., see the following:

different between pointers and pointer to arrays?

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