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:
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
