Pointer to array as function parameter

Question

I wrote a function which takes a pointer to an array to initialize its values:

#define FIXED_SIZE 256
int Foo(int *pArray[FIXED_SIZE])
{
/*...*/
}

//Call:

int array[FIXED_SIZE];
Foo(&array);

And it doesn't compile:

error C2664: 'Foo' : cannot convert parameter 1 from 'int (*__w64 )[256]' to 'int *[]'

However, I hacked this together:

typedef int FixedArray[FIXED_SIZE];
int Foo(FixedArray *pArray)
{
/*...*/
}

//Call:

FixedArray array;
Foo(&array);

And it works. What am I missing in the first definition? I thought the two would be equivalent...

cnicutar · Accepted Answer · 2012-03-16 20:09:16Z

15

int Foo(int *pArray[FIXED_SIZE])
{
/*...*/
}

In the first case, pArray is an array of pointers, not a pointer to an array.

You need parentheses to use a pointer to an array:

int Foo(int (*pArray)[FIXED_SIZE])

You get this for free with the typedef (since it's already a type, the * has a different meaning). Put differently, the typedef sort of comes with its own parentheses.

Note: experience shows that in 99% of the cases where someone uses a pointer to an array, they could and should actually just use a pointer to the first element.

answered Mar 16, 2012 at 20:09

cnicutar

184k26 gold badges378 silver badges399 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Ed Swangren Over a year ago

Yep, pointer to first element as well as the size (if needed, which it probably is).

Knight71 · Accepted Answer · 2013-08-07 12:10:33Z

1

One simple thing is to remember the clockwise-spiral rule which can be found at http://c-faq.com/decl/spiral.anderson.html

That would evaluate the first one to be an array of pointers . The second is pointer to array of fixed size.

answered Aug 7, 2013 at 12:10

Knight71

2,9595 gold badges39 silver badges66 bronze badges

Comments

Mahesh · Accepted Answer · 2012-03-16 20:10:17Z

-1

An array decays to a pointer. So, it works in the second case. While in the first case, the function parameter is an array of pointers but not a pointer to integer pointing to the first element in the sequence.

answered Mar 16, 2012 at 20:10

Mahesh

34.7k23 gold badges94 silver badges116 bronze badges

Collectives™ on Stack Overflow

Pointer to array as function parameter

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related