Thread: Is {0,} okay?

Is this okay? It compiles on my compiler, but of course that doesn't mean anything.

Code:

int array[100] = {0,};

Yes, as long as it is initializing an array. (Whereas {0} works for anything.) It's very much like this.

Code:

   int value[] =
   {
      1,
      2,
      3,
   };

I saw the guy that did that example. I tried something similar on Dev-C++ and I got expected output, but I don't think it's what the guy wanted.

Code:

#include <stdio.h>

int main() {
    
int array[20] = {2,};
int x;

for (x = 0; x < 20; x++)
    printf("%d \n", array[x]);
    
return 0;
}

Output:

Code:

2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0

Of course. This is in section 6.7.8 of the ISO C standard:

21 If there are fewer initializers in a brace-enclosed list than there are elements or members
of an aggregate, or fewer characters in a string literal used to initialize an array of known
size than there are elements in the array, the remainder of the aggregate shall be
initialized implicitly the same as objects that have static storage duration.

And of course we all know that (found in the same section of the standard):

10 If an object that has automatic storage duration is not initialized explicitly, its value is
indeterminate. If an object that has static storage duration is not initialized explicitly,
then:
— if it has pointer type, it is initialized to a null pointer;
— if it has arithmetic type, it is initialized to (positive or unsigned) zero;
— if it is an aggregate, every member is initialized (recursively) according to these rules;
— if it is a union, the first named member is initialized (recursively) according to these
rules.

I know all that, I was just wondering if you were allowed to stick in a trailing comma. I saw someone here do it and was wondering if it was valid.

Thanks.

It's valid. But it's also ugly IMHO

Yes, the trailing comma in initializers is valid.

I figured that out already, from the other posts.

It's valid. But it's also ugly IMHO

Same here.

I also think it's not a very explicit way of saying what you want to do.

You're better off saying:

Array[0] = 0;

No, actually you're not better off that way. All that does is set the first element. The other version initializes all elements in the array.


Quzah.

Ah, but it doesn't. Not the code I compiled, anyway, if you look at my example in my above post.

The guy who initially used the 0, appeared to want to initialize all the elements in the array, but I don't think he got what he expected.

Originally Posted by SlyMaelstrom

I also think it's not a very explicit way of saying what you want to do.

You're better off saying:

Array[0] = 0;

I think it's actually used more often to simulate:

Code:

int array[50];

memset(array, 0, sizeof(int) * 50);

By doing something like:

Code:

int array[50] = { 0 };

Yes I know he wanted it to work like:

Code:

int array[50] = { 0 };

...but it doesn't. That's what I'm saying when I said he didn't get the results he appeared to he wanted.

Adding the comma seems to imply to the compiler that you're trying to initialize a specific element of the array similar to doing:

Code:

int array[5] = { 0, 1, 2, 3, 4 };

No it doesn't.

Code:

#include<stdio.h>
int main( void )
{
    int array[ 10 ] = { 1, };
    int x;
    
    for( x = 0; x < 10; x++ )
        printf("array[ %d ] is %d\n", x, array[ x ] );
    return 0;
}

/*
array[ 0 ] is 1
array[ 1 ] is 0
array[ 2 ] is 0
array[ 3 ] is 0
array[ 4 ] is 0
array[ 5 ] is 0
array[ 6 ] is 0
array[ 7 ] is 0
array[ 8 ] is 0
array[ 9 ] is 0
*/

As I said, it initializes all elements in my example, one in yours.

[edit]
Let's clarify: Are you trying to say, "I think he thinks it will put 2 into every single element.", or what exactly?

The comma has absolutely no effect whatsoever. The standard dictates that if you initialize an element in an array, at declaration time, all those you don't initialize will be set to zero.

So, are you saying he doesn't know that, or what?
[/edit]

Quzah.

This looks like 0-initialized to me:

Code:

2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0