How to throw std::exceptions with variable messages?

Question

This is an example of what I often do when I want to add some information to an exception:

std::stringstream errMsg;
errMsg << \"Could not load config          


        

Answer 1

Ran into a similar issue, in that creating custom error messages for my custom exceptions make ugly code. This was my solution:

class MyRunTimeException: public std::runtime_error
{
public:
      MyRunTimeException(const std::string &filename):std::runtime_error(GetMessage(filename)) {}
private:
      static std::string GetMessage(const std::string &filename)
     {
           // Do your message formatting here. 
           // The benefit of returning std::string, is that the compiler will make sure the buffer is good for the length of the constructor call
           // You can use a local std::ostringstream here, and return os.str()
           // Without worrying that the memory is out of scope. It'll get copied
           // You also can create multiple GetMessage functions that take all sorts of objects and add multiple constructors for your exception
     }
}

This separates the logic for creating the messages. I had originally thought about overriding what(), but then you have to capture your message somewhere. std::runtime_error already has an internal buffer.