Thread: Array length problem

I'm trying to set up two arrays that will store the surname and forename of a person when prompted to enter it. However, because the name could be anything when entered, I don't know what size to make the array. Will I have to do a dynamic array for this, or is there an easier way to do this?

The way I've done it before is based on an example in my text book that tells me that I could do a string as follows:

Code:

char name[] = "John Smith";

, which would create an array with 11 objects of type char.

I figured I could do a similar thing that would have the same idea, but that looks like this,

Code:

char name[];

and then have a scanf where the value was entered, but then it won't compile properly.

If you understand my ramblings - please help me!

Originally Posted by vart

char name[] = "John Smith";

asks a compiler to count number of bytes in the string "John Smith" add one byte for the 0 character, allocate enouhg space for it and copy this string into allocated buffer.

char name [11];
asks compiler to allocate 11 bytes for later use

char name[]; ask compiler to allocate a buffer but does not provide any information about desired buffer size. so compiler shows error that he cannot determine the buffer size to allocate

Yeah I had a feeling thats how it works, just wondered if there was a way of doing it in that sort of manner. I know I could allocate a large amount of memory to it, but that seems like rather a waste of memory. I could also (this is the way I'm trying) ask the user how many letters are in the word that is being inputted. I don't really like this way, and I was just wondering if there is a way to count the number of letters as they're being entered and then assigning the memory to that?

That doesn't sound like too much fun! How I said above that I was going to do it doesn't work. It compiles first, but it now crashes, which isn't a whole lot of laughs either. I might just have a large amount of memory allocated for it. Might be easier.

Not so much no. I'm sure it can cope with about 40 extra bytes being used maybe?

Originally Posted by dwks

How are you reading in "John Smith" from the user? I bet you're using something like this:

Code:

scanf("%s", name);

scanf("%s") only reads until the first whitespace character. That is, "John" will be stored in name, and "Smith" will remain in the input stream. This could cause a problem if, for example, you read John Smith's age right afterwards; scanf() will see "Smith" and conclude that that isn't a number (which it isn't), and return an error code (which you probably don't check for), leaving the age variable unchanged.

To read spaces into name, use fgets() instead of scanf(). http://faq.cprogramming.com/cgi-bin/...&id=1043284385

Code:

#include <stdio.h>  /* for BUFSIZ and fgets() */
#include <string.h>  /* for strchr() */

char name[BUFSIZ], *p;
fgets(name, sizeof(name), stdin);
if((p = strchr(name, '\n')) != 0) *p = 0;  /* remove the newline from name */

When reading numbers from the user, you could discard non-digit input, or use fgets() to read the line and sscanf() to parse it, or something of the like. http://faq.cprogramming.com/cgi-bin/...&id=1043284385

Thats exactly how I was reading in the name, but I've got it so there is an array for forename and one for surname, and two scanf statements.