c++ arry question

[Precious roy]

just wondering why does this not work ?

I want to figure out the size of an array of a strut but it just returns 0

#include "stdafx.h"

struct OBJECT
{
    float X, Y, Z;
};

int blabla(OBJECT test[]);

OBJECT test[230];

int _tmain(int argc, _TCHAR* argv[])
{
	int g = blabla(test);

	return 0;
}

int blabla(OBJECT test[])
{
	int one = sizeof(test);

	int two = sizeof(test[0]);

	int leng = one / two;

	return leng;
}

but when I do it like this it works just fine

#include "stdafx.h"

struct OBJECT
{
    float X, Y, Z;
};

OBJECT test[230];

int _tmain(int argc, _TCHAR* argv[])
{
	int one = sizeof(test);

	int two = sizeof(test[0]);

	int leng = one / two;

	return 0;
}

[jsmith]

In example 2, at line 12 the compiler knows that test is of type OBJECT[230] -- that is, it knows how many elements
there are in the array.

In example 1, line 21 is trying to take the size of its parameter. Its parameter is OBJECT[] -- that is, the size is unknown.
(In fact, the size it returns will be sizeof( OBJECT* ), which will be 4 for a 32-bit platform).

[Precious roy]

hmm that makes sense. any idea on how i can fix this ?

[Computergeek01]

Declare the OBJECT test[] within the _tmain() function of the first example instead of a global variable. Declare the function blabla like this:

int blabla(OBJECT);

This way blabla knows that it is getting an OBJECT passed to it but you don't have to declare it's name.

[jsmith]

You have to make the size known or else pass in the number of elements to the function.

// But now blabla can only take an array of exactly 230 elements.
int blabla( OBJECT test[ 230 ] ) {
    // ...
}

// or
int blabla( OBJECT test[], int numElements ) {
}

// or
template< size_t N >
int blabla( OBJECT test[ N ] )
{
    // This function can only be called with fixed length arrays of any size.
}