PRB: L2029 Caused by Array Index Multiplication with Integers

ID: Q31448

6.00 6.00a 6.00ax 7.00 | 6.00 6.00a | 1.00 1.50

MS-DOS                 | OS/2       | WINDOWS

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The information in this article applies to:

The Microsoft C/C++ Compiler (CL.EXE), included with:

    - Microsoft C for MS-DOS, versions 6.0, 6.0a, and 6.0ax
    - Microsoft C for OS/2, versions 6.0 and 6.0a
    - Microsoft C/C++ for MS-DOS, version 7.0
    - Microsoft Visual C++ for Windows, versions 1.0 and 1.5

SYMPTOMS

An attempt to declare an array with a constant expression fails and an error occurs. In C/C++ versions 7.0 and 8.0, the compiler generates the following messages:

   warning C4307: '*' : integral constant overflow; result
      truncated
   error C2466: cannot allocate an array of constant size 0

In C versions 5.0, 5.1, 6.0, 6.0a, and 6.0ax, Microsoft LINK generates the following message:

   L2029: unresolved external for the variable <variablename>

CAUSE

The errors occur because the result of the constant expression that specifies the array size is too large for an integer value.

RESOLUTION

Declare one or more of the integer constants in the expression with data type long. When this is done, the compiler calculates the expression using long integer math instead of integer math.

MORE INFORMATION

The code example below demonstrates this problem. Because the value of the expression 256*512 is an exact multiple of 65,536, the compiler treats it as the value 0.

Sample Code

/*
 * Compile options needed: none
 */ 

   char huge arr[256*512];

The code example below demonstrates the correct method to declare a huge array.

Sample Code

/*
 * Compile options needed: none
 */ 

   char huge arr[256l*512];

Additional reference words: 1.00 1.50 6.00 6.00a 6.00ax 7.00 KBCategory: kbprg kbprb KBSubcategory: CLngIss Keywords : kb16bitonly

Last Reviewed: July 18, 1997