Article: Q112337
Product(s): Microsoft C Compiler
Version(s): 1.0,2.0
Operating System(s):
Keyword(s): kbCRT kbVC
Last Modified: 27-FEB-2002
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The information in this article applies to:
- The C Run-Time (CRT), included with:
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0
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SYMPTOMS
========
Attempting to replace the default _matherr function with a user-defined version
and then linking with the C run-time dynamic-linked library (DLL) causes the
compiler to issue the following warning:
warning C4273: '_matherr' : inconsistent dll linkage. dllexport assumed.
Running the resultant executable causes the default _matherr to be used rather
than the user-defined version.
CAUSE
=====
The compiler issues the C4273 warning because of the way the _matherr function
is prototyped in the MATH.H header file. _matherr has the following prototype:
_CRTIMP int __cdecl _matherr(struct _exception *);
When code is being compiled to be used with the C run-time DLL, _CRTIMP is
defined to be the following:
__declspec(dllimport)
When code is being compiled to be used with one of the statically linked C
run-time libraries, _CRTIMP is defined to be nothing.
The C4273 warning is generated because the compiler has detected a redefinition
of _matherr after already seeing a prototype that specifies that _matherr is
being imported.
RESOLUTION
==========
It is not possible to replace the default version of _matherr when using the
dynamically linked version of the C run-time library.
The README.WRI file supplied with Visual C++, 32-bit Edition, version 1.0, gives
the following information:
Using _matherr with CRTDLL.DLL
If you use the dynamically linked version of the C run-time
library (CRTDLL.DLL), you cannot replace the default _matherr
routine with a user-defined version. You can only install a
custom _matherr routine if you use one of the statically linked C
run-time libraries.
CRTDLL.DLL is the name of the C Run-time DLL that is supplied with Windows NT.
The C Run-time DLL supplied with version 1.0 of Visual C++, 32-bit Edition, is
called MSVCRT10.DLL and the name of the C Run-time DLL supplied with version 2.0
of Visual C++, 32-bit Edition is MSVCRT20.DLL. The limitation of not being able
to replace _matherr pertains only to using MSVCRT*.DLL.
MORE INFORMATION
================
The following sample code can be used to demonstrate the problem.
Sample Code
-----------
/* Compile options needed: /MD
*/
#include <math.h>
#include <string.h>
#include <stdio.h>
void main()
{
// Do a math operation that causes an error
printf( "log( -2.0 ) = %e\n", log( -2.0 ) );
}
int _matherr( struct _exception *except )
{
/* Handle _DOMAIN errors for log */
if( except->type == _DOMAIN )
{
if( strcmp( except->name, "log" ) == 0 )
{
except->retval = log( -(except->arg1) );
printf( "Special: using absolute value: %s: _DOMAIN "
"error\n", except->name );
return 1;
}
}
else
{
printf( "Normal: " );
return 0; /* Else use the default actions */
}
return 0;
}
REFERENCE
---------
For additional information, please see the following article in the Microsoft
Knowledge Base:
Q112297 INFO: User Defined CRT Function Causes Unresolved External
Additional query words: _matherrl
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Keywords : kbCRT kbVC
Technology : kbVCsearch kbAudDeveloper kbCRT
Version : :1.0,2.0
Issue type : kbprb
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