BUG: Based Ptr. Init Fails at Global Scope in CPP File

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View products that this article applies to.

This article was previously published under Q116172

SYMPTOMS

When attempting to compile an application written in C++ that contains a based pointer initialized at global scope, the compiler incorrectly returns the error message

error C2440 : 'initializing' : cannot convert from 'int __far *' to 'int __based(xxxx) *'

where xxxx is the segment on which the pointer is based.

This error does not occur for based pointers that are initialized at function scope.

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With the 16-bit compilers listed above, this error can be eliminated by typecasting the constant that is used to initialize the based pointer to a type "_based(void) *". The following code demonstrates how to generate the compiler error as well as the workaround:

/* Compile options needed:   none
*/ 

// Base Pointer
int *BasePtr;

// This line compiles fine (no initialization)
int _based(BasePtr) *test1;

// This line generates an C2440 error
int _based(BasePtr) *test2=0;

// This line demonstrates the 16 bit workaround
int _based(BasePtr) *test3 = (int _based(void) *)0;

void main(void)
{
// Initialization at file scope does not generate C2440

   int _based(BasePtr) *test4 = 0;
}

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Sample Code 2

In the 32-bit compiler for Windows NT, version 8.0, the workaround given for the 16-bit compilers does not work. The "_based(void) *" cast generates the following two error messages if you are using the 32-bit compiler:

error C2493: illegal form of __based error C2440: 'initializing' : cannot convert from 'int *' to 'int __based(BasePtr) *'

In this case, the file scope based pointer cannot be declared and initialized in one step. An appropriate workaround would be to declare the pointer at file scope and initialize the pointer inside of a function. The following code demonstrates how to generate the compiler error as well as the workaround:

/* Compile options needed: none
*/ 
// Base Pointer
int *BasePtr;

// This line compiles fine (no initialization).
int _based(BasePtr) *test1;

// This line generates C2440 error.
int _based(BasePtr) *test2=0;

// This line generates C2440 and C2493 errors.
int _based(BasePtr) *test3 = (int _based(void) *)0;

void main(void)
{
// 32-bit workaround: initialize the based pointer at function scope.

   test1 = 0;

// Initialization at file scope does not generate C2440 or C2493.

   int _based(BasePtr) *test4 = 0;
}

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

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APPLIES TO

Microsoft Visual C++ 1.0 Professional Edition
Microsoft Visual C++ 1.5 Professional Edition
Microsoft Visual C++ 2.0 Professional Edition
Microsoft Visual C++ 4.0 Standard Edition
Microsoft Visual C++ 4.1 Subscription
Microsoft Visual C++ 4.2 Professional Edition

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kbbug kbcompiler kbcpponly KB116172

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Retired KB Content Disclaimer

This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.

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