CODEWITHSUNDEEP
carraysfunction
OldSchool
OldSchool

Reputation: 2183

how to calculate size of array which is passed to a function

Have a look at following code

void fun( int *p )
{
    // is there any solution to calculate size of array as we are not explicitly passing its size.
}

void main ()
{
    int a[5];
    fun (a);
}

Is there any solution to calculate size of array in function or explicitly passing its size is the only solution?

Upvotes: 2

Views: 85

Answers (3)

ajay
ajay

Reputation: 9680

When you pass an array to a function, the array is implicitly converted to a pointer to its first element. Thus what you are actually passing is a pointer to the first element of the array, not the array itself. In fact, you can't pass to or return an array from a function. They are not first class objects in C. Hence, you must pass the length of the array to the function as well.

void fun(int *p, int len) {
    // function body
}

int main(void) {
    int a[5];
    fun(a, 5);
}

Upvotes: 3

herohuyongtao
herohuyongtao

Reputation: 50657

You cannot.

It's just one pointer, which contains no size info of the array. That's why it's a common implementation to pass the size of the array as a second parameter to the function.

Upvotes: 3

user2357112
user2357112

Reputation: 280301

The pointer p contains no data about the size of the array. You don't quite have to pass the size as a parameter - you could end the array with a 0 like strings do, or hardcode the length, or do any of a number of other things - but without some sort of additional machinery, you can't get the length from just a pointer.

Upvotes: 3

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