Difference between revisions of "Microsoft KB Archive/43703"

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A similar solution may be applied to the problem of dynamically allocating a multidimensional array. For example, the following code fragment allocates a memory block, which can be used as a 10 x 20 x 30 three- dimensional array:
 
A similar solution may be applied to the problem of dynamically allocating a multidimensional array. For example, the following code fragment allocates a memory block, which can be used as a 10 x 20 x 30 three- dimensional array:
<pre class="codesample">#include &lt;malloc.h&gt;
+
<pre class="codesample">#include <malloc.h>
  
 
typedef char (*Ptr3Dim) [20][30] ;
 
typedef char (*Ptr3Dim) [20][30] ;

Latest revision as of 10:19, 21 July 2020

Knowledge Base


INFO: Casting a Pointer to Type Equivalent to Multidimensional

Article ID: 43703

Article Last Modified on 7/5/2005



APPLIES TO

  • Microsoft C Professional Development System 6.0a
  • Microsoft Visual C++ 1.0 Professional Edition
  • Microsoft Visual C++ 1.5 Professional Edition
  • Microsoft Visual C++ 1.51
  • Microsoft Visual C++ 1.52 Professional Edition
  • Microsoft Visual C++ 2.0 Professional Edition
  • Microsoft Visual C++ 2.1
  • Microsoft Visual C++ 4.0 Standard Edition
  • Microsoft Visual C++ 5.0 Enterprise Edition
  • Microsoft Visual C++ 6.0 Enterprise Edition
  • Microsoft Visual C++ 5.0 Professional Edition
  • Microsoft Visual C++ 6.0 Professional Edition
  • Microsoft Visual C++ 6.0 Standard Edition



This article was previously published under Q43703


SUMMARY

In some situations you may need to cast a pointer or an address to a type that is equivalent to a multidimensional array. The following example demonstrates such a situation:

typedef char Arr2Dim [][20] ;
void myfunc (Arr2Dim) ;
char * ptr ;
...
void main (void)
{
    ...
    myfunc ( (Arr2Dim) ptr ) ;  /* illegal */ 
    ...
}
                

Casting the variable "ptr" to the array type "Arr2Dim" is not correct. The Microsoft C Compiler displays the following error message:

error C2067: cast to array type is illegal

The correct procedure is to cast the pointer "ptr" to a pointer type equivalent to the array type Arr2Dim. This pointer type can be defined as follows:

   typedef char (*Ptr2Dim) [20] ;
                

Casting "ptr" to the type of "Ptr2Dim", as follows, is correct and produces no warning messages when compiled at warning level 3:

   myfunc ( (Ptr2Dim) ptr ) ;
                

The address (or pointer) passed to the function is used correctly.

MORE INFORMATION

A similar solution may be applied to the problem of dynamically allocating a multidimensional array. For example, the following code fragment allocates a memory block, which can be used as a 10 x 20 x 30 three- dimensional array:

#include <malloc.h>

typedef char (*Ptr3Dim) [20][30] ;
Ptr3Dim ptr3arr ;
...
void main (void)
{
    ...
    ptr3arr = (Ptr3Dim) malloc (10 * sizeof(char) * 20 * 30) ;
    ...
}
                

After the allocation, "ptr3arr" can be used as a three-dimensional array, as follows, provided i, j, and k are integers within the proper range:

   ptr3arr [i][j][k] = 'a' ;
                

Keywords: kbinfo kblangc KB43703