Code Complete, 2nd Edition

Global Data

Global variables are accessible anywhere in a program. The term is also sometimes used sloppily to refer to variables with a broader scope than local variables—such as class variables that are accessible anywhere within a class. But accessibility anywhere within a single class does not by itself mean that a variable is global.

Cross-Reference

For details on the differences between global data and class data, see "Class data mistaken for global data" in Design Building Blocks: Heuristics.

Most experienced programmers have concluded that using global data is riskier than using local data. Most experienced programmers have also concluded that access to data from several routines is pretty useful.

Even if global variables don't always produce ...