Buffered input

[CeeCee]

Simple question concerning input. Say I declare a buffer to be of size 1024, and I'm sure that the input will almost always be less than that.
My question is if I plan to work a lot with that buffer, will I need to initialize it to null characters to avoid getting garbage after processing?

[Stoned_Coder]

i would always initialise a buffer completely. Any help against bugs creeping in has to be a good thing.

[Garfield]

Yeah, better to be safe than sorry.

>> C code. C code run. run code, run...please! <<

That is great! I wish I thought of that.

---Garfield

[CeeCee]

What's the best way to do that? As far as I understand, the best way is to use a for loop.

for(i = 0; i < 1024; i++){buf[i] = '\0';}

[Salem]

If all you are doing is passing that buffer to fgets for example, then clearing it before hand (or even before each fgets call) adds nothing.

fgets always adds a \0, and there is never anything useful after that (nor should you be looking there either), so there shouldn't be a problem.

[Garfield]

Well, yes, that would be the way to do it...if you used a char aray []. But, if you were to use a char *, you would just need to do:

char *string;

/***init string***/

string = NULL;

All you have to do is init a pointer as NULL.

--Garfield

[CeeCee]

@Salem - Yes, I use fgets to fill my char arrays. That's nice to know, thank you.

@Garfield - My question was about char arrays, not char pointers. Since either you initialize a char pointer to a string when you create it, or use it as a pointer to an existing variable, the question of whether or not to initialize it to nulls is moot. Though I always initialize my pointers to null pointers when I create them so that I can't accidentally try to use a value that I don't want without knowing.

Though I do have a followup for the answer you brought up Garfield. If I have a ragged array, is there a way to clear it to nulls or is there no need?
char *array[10];

[QuestionC]

Hmm. I haven't tried this, but I think this will initialize all the elements of the array to NULL.

char * array[10] = {};

[CeeCee]

And that would work for any array type?
char array[1024] = {};
etc...

Anyway, I was under the impression that any array declared with global or extern scope will automatically be initialized to all 0, and anything with local or automatic scope is undefined until explicitly initialized.
With that in mind, how does placing nothing inside the {} cause the array to fill with NULL?

[Salem]

That would be
char array[1024] = { 0 }; // 1024 '\0' bytes

or
char * array[10] = { 0 }; // 10 NULL pointers

[doubleanti]

hm... salem, is there a standard on uninitialized values of a particular type? i know that for many of the base types there is no value rectification... also, if you know what's to be in the buffer, when the input procedures end, all you'd need to do is append the final null in order to get correct stoppage... but it depends on your implementation...

[Salem]

> is there a standard on uninitialized values of a particular type?
Given
<any_base_type_or_pointer_to_base_type> array[1024] = { 0 };
The compiler will cast the 0 to be a proper 0.0 in the case of floats/doubles, and a proper NULL in the case of pointer types.

Note that this is different than filling the array with say memset.
http://www.eskimo.com/~scs/C-faq/q7.31.html

If you've got K&R - 2nd Ed, read A8.7

[Unregistered]

there is a few ways to initialize a string to 0...

char str[1024] = "\0";

and if you want to set it to totally null afterwards:
memset(str, 0, 1023);