How do I get a std::exception error description when calling a C++ dll from C#

Question

I have a C# application which calls a function in a C++ dll. This function can throw various exceptions which inherits std::exception. I currently catch these exceptions like this:

try
{
    //Call to C++ dll
}
catch (System.Exception exception)
{
    //Some error handling code
}

My first question is will this code catch all std::exception? My second question is how can I retrieve the std::exception::what string, if I examine exception.Message I only get "External component has thrown an exception".

EDIT: The function in question is in a non managed C++ dll, and imported like this in the C# class:

[DllImport("SomeDLL.dll")]
public extern static void SomeFunction();

There is a ToString method returns a string representation of the current exception. http://msdn.microsoft.com/en-us/library/system.exception_members.aspx — DumbCoder, Aug 20 '10 at 08:15
http://stackoverflow.com/questions/150544/can-you-catch-a-native-exception-in-c-code/150596#150596 — celavek, Aug 20 '10 at 08:25

score 1 · Answer 1 · answered Jun 30 '11 at 08:37

1

The best way to go would be to handle the exception in C++, and save the error message somewhere. Then, in C# you can check if there was an error message saved, and if it was you can retrieve it.

C++:

try
{
    //do some processing
}
catch(std::exception& ex)
{
    // errorMessage can be a std::string
    errorMessage = ex.what();
}

C#:

[DllImport("SomeDLL.dll")]
public extern static void SomeFunction();
[DllImport("SomeDLL.dll")]
public extern static string GetError();

SomeFunction();
string Error = GetError();
if(String.IsNullOrEmpty(Error)==true)
{
    //The processing was successfull
}
else
{
    //The processing was unsuccessful
    MessageBox.Show(Error);
}

answered Jun 30 '11 at 08:37

Ove

6,227
2
39
68

And what if it is a third party code I have no possibility to modify it? – Tomas Kubes May 03 '16 at 11:52
Link against the library in your own C++ wrapper library. – Siddhartha Gandhi May 05 '20 at 23:52
This work as well the other way around: catching c# exception from c++ native code. You need to activate SEH exception to work correctly. In the c# wrapper, I save the ex->Message to char * member (using Marshal::StringToHGlobalAnsi) and return with get method. In c++ in "catch(...)" block I read the exception by the get method and throw a std::exception with that message. – Fil May 06 '20 at 13:21

score 0 · Answer 2 · answered Aug 20 '10 at 08:20

0

Call how? The CLR doesn't really "get" C++ exception handling. If you call the C++ code through COM, add a layer that catches the std::exception and wrap it with a HRESULT/IErrorInfo. If you call it through managed C++, add a layer that wraps it in a managed System.Exception etc.

answered Aug 20 '10 at 08:20

Mattias S

4,748
2
17
18

1

The same principle applies to PInvoke. It's easier to find some other protocol for error reporting. Using the return values, output parameters and/or Windows' SetLastError function for example. – Mattias S Aug 20 '10 at 11:13

How do I get a std::exception error description when calling a C++ dll from C#

2 Answers2