_matherr does not get called when built into a DLL

Question

I have a basic solution file (.sln) where I was able to reproduce a problem I have been facing recently.

It contains 3 projects: 1.) MathTest.lib - containing methods that might cause a mathematical error, like acos(1.1). 2.) MathTestDll.dll - calls the methods from the above lib. 3.) UnitTest.exe - calls the exported method in the DLL that should cause the error.

What I'm trying to do is fairly simple: The following code contains the _matherr() routine and should ideally link fine. The call to acos() with a value of 1.1 is invalid (invalid input) and should cause an error which should be handled by the implemented _matherr() handler. I hope I'm right about the behavior of _matherr(). Please let me know. MathTest.lib

#include "MathTest.h"
#include <iostream>
#include <math.h>

int _matherr(_exception* _Except)
{
    std::cout << _Except->name;
    return -1;
}

void MathTest::ThrowMatherr(float par)
{
    float result = acos(par);
    std::cout << result;
}

This 'ThrowMatherr()' method will be called by the DLL as follows: MathTestDll.dll

void MatherrCaller::CauseMatherr()
{
    MathTest* mathtest = new MathTest();
    mathtest->ThrowMatherr(1.1);
}

which is then exported as:

extern "C" __declspec(dllexport) void CallThisToCauseMatherr();

void CallThisToCauseMatherr()
{
    MatherrCaller* caller = new MatherrCaller();
    caller->CauseMatherr();
}

This exported method will be called by a simple test. UnitTest.exe

#include <windows.h>

typedef void (*METHODTOCALL)(); 

int main()
{
    HMODULE module = LoadLibrary((LPCSTR)"..\\Debug\\MatherrTestDll.dll");
    if(module != NULL)
    { 
        METHODTOCALL ProcAdd = (METHODTOCALL) GetProcAddress(module, (LPCSTR)"CallThisToCauseMatherr"); 
        if (NULL != ProcAdd)
        {
            (ProcAdd)();
        }

        FreeLibrary(module); 
    }

    return 0;
}

All methods get called fine. But the acos() method which has been passed invalid input never calls the _matherr() error handler. Please let me know how I can fix this.

I had to make the question detailed to get my point through. Please don't mind.

Answer 1

It is explicitly mentioned in the documentation for _matherr:

For special error handling, you can provide a different definition of _matherr. If you use the dynamically linked version of the C run-time library (Msvcr90.dll), you can replace the default _matherr routine in a client executable with a user-defined version. However, you cannot replace the default _matherr routine in a DLL client of Msvcr90.dll.

You'll need to put the override in the EXE module. Alter your unit test to accommodate this.