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Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.

_countof Macro 

Compute the number of elements in a statically-allocated array.


_countof( 
      array
);

Parameters

array

The name of an array.

The number of elements in the array.

Ensure that array is actually an array, not a pointer. In C, _countof will produce erroneous results if array is a pointer. In C++, _countof will fail to compile if array is a pointer.

Macro Required header Compatibility

_countof

<stdlib.h>

Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition, Windows NT 4.0, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003

// crt_countof.cpp
#define _UNICODE
#include <stdio.h>
#include <stdlib.h>
#include <tchar.h>

int main( void )
{
   _TCHAR arr[20], *p;
   printf( "sizeof(arr) = %d bytes\n", sizeof(arr) );
   printf( "_countof(arr) = %d elements\n", _countof(arr) );
   // In C++, the following line would generate a compile-time error:
   // printf( "%d\n", _countof(p) ); // error C2784 (because p is a pointer)

   _tcscpy_s( arr, _countof(arr), _T("a string") );
   // unlike sizeof, _countof works here for both narrow- and wide-character strings
}

Output

sizeof(arr) = 40 bytes
_countof(arr) = 20 elements

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