Microsoft KB Archive/112337

= PRB: /MD Causes C4273 Warning When Replacing _matherr =

Article ID: 112337

Article Last Modified on 11/18/2003

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APPLIES TO

 The C Run-Time (CRT), when used with:  Microsoft Visual C++ 1.0 Professional Edition

 Microsoft Visual C++ 2.0 Professional Edition 

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This article was previously published under Q112337



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: <pre class="fixed_text">  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.

<div class="moreinformation_section">

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:

112297 INFO: User Defined CRT Function Causes Unresolved External

Additional query words: _matherrl

Keywords: kbcrt kbprb KB112337

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