Catching all exceptions and logging information

Question

I am a Java programmer working with C++ code, and need some help with exception handling.

I have code in the following structure:

try{
...
}
catch( ... ) 
{
    log("Exception occurred");
}

An exception is occurring, but the try block is really massive and debugging is not an option, so I need to minimally modify the code to give me relevant info on the exception.

So I added the following catch block before the existing catch block (working with my Java knowledge and referring to C++ guides):

catch(exception e)
{
    log(e.what());
}

However, I am still getting the old message - "Exception occurred". The code in try block contains a lot of low level functions like strncpy, memcpy etc.

Why is this catch block not working as expected? What can I do to get information on the exception that is occurring and on which line, similar to the stack trace that Java so easily gives.

Answer 1

First, you should catch by reference (generally const), so your new catch block should read:

try {

} catch(std::exception const& e) {
    log(e.what());
} catch(...) {
    log("Exception occurred");
}

Second, in C++ you may throw any value. Even of type int. If your codebase include such unsavvy throw statements, I pity you.

Since you come from Java, I would check if you mistakenly used a throw new XXXX which would throw a pointer (to a dynamically allocated value) instead of a value. The new is unnecessary in C++.

Answer 2

Probably because those exceptions are not derived from exception class. In C++ any type can be an exception, for example string, int, etc. Anyway if you want to catch exception you should probably catch a reference to the exception &.

Answer 3

You will have to debug and determine if the exception is an C++ exception.
Note that divide by 0 etc are runtime exceptions not supported by C++, so it can be anything literally.

A catch-all handler will only catch valid C++ exceptions not all exceptions(which can be plenty).