_countof Macro

Article
06/05/2017

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The latest version of this topic can be found at _countof Macro.

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

Syntax

size_t _countof(   
   array  
);

Parameters

array
The name of an array.

Return Value

The number of elements in the array, expressed as a size_t.

Remarks

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.

Requirements

Macro	Required header
`_countof`	<stdlib.h>

Example

// crt_countof.cpp  
#define _UNICODE  
#include <stdio.h>  
#include <stdlib.h>  
#include <tchar.h>  
  
int main( void )  
{  
   _TCHAR arr[20], *p;  
   printf( "sizeof(arr) = %zu bytes\n", sizeof(arr) );  
   printf( "_countof(arr) = %zu elements\n", _countof(arr) );  
   // In C++, the following line would generate a compile-time error:  
   // printf( "%zu\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  
}

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

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