Passing a pointer to a 2D array

What is the correct way to pass a pointer to 2D array?

What I do:

float X[length][length]

foo(&X);

Error:

warning: passing argument 1 of ‘foo_’ from incompatible pointer type

The program will still compile and run properly, but I hate these compilation errors.

Check out the tutorials.

Code:

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int x[M][N];

void func(int y[M][]);

func(x);

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That's for passing an array.

I need a pointer to an array,

Quote:

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Originally Posted by dwks

Check out the tutorials.

Code:

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int x[M][N];

void func(int y[M][]);

func(x);

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Perhaps you meant:

Code:

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void func(int y[][N])

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Quote:

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Originally Posted by OakRand

That's for passing an array.

I need a pointer to an array,

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How do you think arrays are passed?

Code:

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void func(int (*y)[N])

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[edit]http://c-faq.com/aryptr/pass2dary.html

I don't need to know how to define the function, but how to specify the 2d array as a pointer in the function call.

Code:

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void func(int (*y)[N]);
...............
int array[M][N];
func(array);

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From, what I can gather from the lack of usefull responces to my thread on the type of a 2D array, there is no way to do this.

Stop spamming the forums with your whining. You've already been answered.

[To the OP]
As to this topic, there are different ways to interpret this. Do you want a "pointer to a two dimensional array", or do you just want a function to accept a 2D array? They are two different things. Consider:

Code:

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void foo( int x );

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This function cannot update the variable 'x' passed to it so it affects the variable outside the function. That is why we must use a pointer to it:

Code:

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void foo( int *x );

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This is not true for arrays. Arrays degrade to a pointer to the first element, thus, changes to them affect the array itself. Thus:

Code:

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void foo( int array[] );

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Any changes to the array passed to this function will affect the origional array. Therefore, we don't need a pointer to an array. We can have one however...

Code:

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void foo( int (*p2a)[] );

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This is (takes, rather) a pointer to an array of integers.

You can also have a pointer to a two dimensional array. Is that really what you want? Or is all you want is a way to pass an array to a function?
[/To the OP]

Now, back to you. Shut the hell up and stay in your own thread. Your question is in no way related to this, so stop trying to garner sympathy.


Quzah.

> What is the correct way to pass a pointer to 2D array?
> float X[length][length]
> foo(&X);
Is there some benefit to passing a pointer to the array rather than the array itself?
Remember, arrays are always passed as a pointer, so foo(X) and foo(&X) achieve pretty much the same effect.

Yes, you can use an & if you really want to, providing you declare the function properly in the first place.

Code:

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#include<stdio.h>
#define LEN 10

void f1 ( int a[LEN][LEN] ) {
  a[0][0] = 0;
}
void f2 ( int a[][LEN] ) {
  a[0][0] = 0;
}
void f3 ( int (*a)[LEN] ) {
  a[0][0] = 0;
}
void f4 ( int (*a)[LEN][LEN] ) {
  // watch the extra level of indirection needed
  (*a)[0][0] = 0;
}

int main ( void ) {
  int arr[LEN][LEN];
  f1( arr );
  f2( arr );
  f3( arr );
  f4( &arr );
  return 0;
}

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