When I am trying to pass two dimensional array as a parameter In C,
void PrintTriangle(int *triangle)
It's doesn't works for me why ?
3 Answers
You must specify the dimension of the outermost array when passing multidimensional arrays as parameters
Something like this:-
void PrintTriangle(int pascalTriangle[][5]);
Calling PrintTriangle(pascalTriangle); like this is wrong as your function PrintTriangle() is expecting a pointer to integer.
4 Comments
TheCrackNuts
so how do you specify the dimension ?
Rahul Tripathi
@haccks:- The reason why it is wrong is very similar to what you mentioned. Still updated that in my answer!!! Thanx!! :)
Eric Postpischil
The last dimension is for the innermost array, not outermost. In
int a[2][3], a[i] is an aggregate object that is an array of three int. So arrays corresponding to the last dimension are inside the arrays of previous dimensions.Here's how I memorized passing multidemensional arrays as parameters. This might be a little childish but works for me.
Suppose You have an array defined
int numbers[3][4];
and you want to pass it to function.
To do it correctly I answer series of questions:
1) What do I want to pass to function? An array.(in this case numbers).
2) What's numbers? Numbers is an address of its first element(without going into details);
3)What's the first element of numbers?(in this case it's an array of 4 integers)
4) So what I want as function formal parameter is a pointer to answer from step 3:
int (*pointer)[4]
It might be slow and looks unprofessional but you can ask the same question on array of every dimension you can think of. It's also useful to ask yourself that when not passing whole array but one of subarrays.
Hope it helps you as it helped me.
2 Comments
Eric Postpischil
You can simple declare the parameter the same way the array is declared:
void foo(int numbers[3][4]);. The compiler will automatically adjust it to int (*numbers)[4].
zubergu
@EricPostpischil as I mentioned, it's not fast nor smart, just something that I used when learned about multidimensional arrays myself.Helped me to understand pointers and arrays of any size better. Also, it leaves almost no place for silly mistakes.
Calling your function as
PrintTriangle(pascalTriangle);
is wrong. Because PrintTriangle() expecting a pointer to integer as its argument and pascalTriangle (after decaying) is of type int(*)[5].Also you must have to pass the number of rows and columns (as arguments) in array pascalTriangle. Prototype for this function should be
void PrintTriangle(int row, int col, int *triangle);
and a call to it may be
PrintTriangle(5, 5, &pascalTriangle[0][0]);
5 Comments
haccks
@H2CO3; Ya. I know, and you know what that mean in fact :)
Eric Postpischil
C does not require you to pass the number of rows and columns of a two-dimensional array, just the number of columns. (The called function might require it for other reasons.)
printTriangle? Posting your code/snippet may help us to answer this question.