Why use prefixes on member variables in C++ classes

Question

A lot of C++ code uses syntactical conventions for marking up member variables. Common examples include

• m_memberName for public members (where public

Answer 1

Our project has always used "its" as a prefix for member data, and "the" as a prefix for parameters, with no prefix for locals. It's a little cutesy, but it was adopted by the early developers of our system because they saw it used as a convention by some commercial source libraries we were using at the time (either XVT or RogueWave - maybe both). So you'd get something like this:

void
MyClass::SetName(const RWCString &theName)
{
   itsName = theName;
}

The big reason I see for scoping prefixes (and no others - I hate Hungarian notation) is that it prevents you from getting into trouble by writing code where you think you're referring to one variable, but you're really referring to another variable with the same name defined in the local scope. It also avoids the problem of coming up with a variable names to represent that same concept, but with different scopes, like the example above. In that case, you would have to come up with some prefix or different name for the parameter "theName" anyway - why not make a consistent rule that applies everywhere.

Just using this-> isn't really good enough - we're not as interested in reducing ambiguity as we are in reducing coding errors, and masking names with locally scoped identifiers can be a pain. Granted, some compilers may have the option to raise warnings for cases where you've masked the name in a larger scope, but those warnings may become a nuisance if you're working with a large set of third party libraries that happen to have chosen names for unused variables that occasionally collide with your own.

As for the its/the itself - I honestly find it easier to type than underscores (as a touch typist, I avoid underscores whenever possible - too much stretching off the home rows), and I find it more readable than a mysterious underscore.