Are global variables bad? [closed]

Question

In C/C++, are global variables as bad as my professor thinks they are?

Answer 1

Global variables are generally bad, especially if other people are working on the same code and don't want to spend 20mins searching for all the places the variable is referenced. And adding threads that modify the variables brings in a whole new level of headaches.

Global constants in an anonymous namespace used in a single translation unit are fine and ubiquitous in professional apps and libraries. But if the data is mutable, and/or it has to be shared between multiple TUs, you may want to encapsulate it--if not for design's sake, then for the sake of anybody debugging or working with your code.

Answer 2

security is less means any one can manipulate the variables if they are declared global , for this one to explain take this example if you have balance as a global variable in your bank program the user function can manipulate this as well as bank officer can also manipulate this so there is a problem .only user should be given the read only and withdraw function but the clerk of the bank can add the amount when the user personally gives the cash in the desk.this is the way it works

Answer 3

If it's possible your code will end up under intensive review during a Supreme Court trial, then you want to make sure to avoid global variables.

See this article: Buggy breathalyzer code reflects importance of source review

There were some problems with the style of the code that were identified by both studies. One of the stylistic issues that concerned the reviewers was the extensive use of unprotected global variables. This is considered poor form because it increases the risk that the program state will become inconsistent or that values will be inadvertently modified or overwritten. The researchers also expressed some concern about the fact that decimal precision is not maintained consistently throughout the code.

Man, I bet those developers are wishing they hadn't used global variables!

Answer 4

I'd answer this question with another question: Do you use singeltons/ Are singeltons bad?

Because (almost all) singelton usage is a glorified global variable.

Answer 5

The problem with global variables is that since every function has access to these, it becomes increasingly hard to figure out which functions actually read and write these variables.

To understand how the application works, you pretty much have to take into account every function which modifies the global state. That can be done, but as the application grows it will get harder to the point of being virtually impossible (or at least a complete waste of time).

If you don't rely on global variables, you can pass state around between different functions as needed. That way you stand a much better chance of understanding what each function does, as you don't need to take the global state into account.

Answer 6

Use of Global variables actually depends on the requirements. Its advantage is that,it reduces the overhead of passing the values repeatedly.

But your professor is right because it raises security issues so use of global variables should be avoided as much as possible. Global variables also create problems which are sometimes difficult to debug.

For example:-

Situations when the variables values is getting modified on runtime. At that moment its difficult to identify which part of code is modifying it and on what conditions.