Is passing global variables to functions problematic?

Question

Consider following function declaration:

int abmeld(char *strsend) 

which is called like this

abmeld(str); 

where str is a global variable declared and initialised at the start of the program file (after the includes) like this:

char str[300] = ""; 

Now I already know this is unnecessary code (you can access and modify the char array from within any function without passing it anyways), but is this actually otherwise problematic?

Are there consequences (like hard error possibilities, or undefined behavior) that can happen as the result of passing an already globally scoped variable to a function?

Answer 1

I would say the opposite, it is almost never problematic to pass a global to a function (and it is usually dirty to use a lot of globals, the code becoming unreadable).

A function which depends lightly (or not at all) on the global state is often more readable and more understandable than a function using a lot of global (or even static) variables. A global variable changed in many functions makes your program messy to understand.

^{(never forget that you code not only for the computer, but also for your colleagues -perhaps even yourself in a few months- who would have to improve your source code)}

Also, functions using global state are typically not reentrant.

At last, undefined behavior is mostly orthogonal to global vs argument data. In particular, a buffer overflow can occur both with a global variable, or with a pointer to some array (such as an argument or some local variable) .

^{A very crude rule of thumb would be to avoid loading the developer's brain with more than 7 items (magical number 7, + or - 2); hence the folklore rule to avoid more than 7 arguments or more than 7 globals.}