CustomException headerfile

Question

Obviously something goes wrong with my understanding of this topic, but I can't find out where. The thing I want to implement is a custom Exception called CustomException. What I have made does compile and can work, but I do think that I am making use of header files the wrong way. So I have made the following 3 files:

1. main.cpp

   #include "exception.h"
   
   int main() {
       try {
           throw CustomException();
       } catch (CustomException ce) {
           ce.doSomething();
       }
   }
   

2. exception.h

   #include <exception>
   
   class CustomException : public std::exception {
       private:
           char* msg;
       public:
           CustomException() {};
           void doSomething() {};
   };
   

3. exception.cpp

   #include "exception.h"
   
   CustomException::CustomException() {
   }
   
   void CustomException::doSomething() {
       printf("Hello World!");
   }
   

After I run this is the command line:

$ g++ main.cpp -o main.o
$ ./main.o
$

But the behaviour that I was looking for is, that "Hello World!" is printed to the command line. I am more used to JAVA, so maybe that is why I have a rough start with C++. Anyways I hope you can help me, because the tutorials I found differ from each other and don't make sense to me.

Answer 1

Your problem is that you're defining CustomException::doSomething() to do nothing: {}. Leave out the {} method definitions in exception.h. Then compile and link exception.cpp into your binary:

$ g++ -c main.cpp -o main.o
$ g++ -c exception.cpp -o exception.o
$ g++ main.o exception.o -o main
$ ./main

Note that a ".o" suffix is normally used for object files, not for executables.

Answer 2

In addition to what user3553031 said, there is another posslble problem with your code. In C++ you should catch exceptions by reference, not by value. Otherwise it can cause problems. See this: C++ catch blocks - catch exception by value or reference?