Question

Why do some people declare make their variables static, like so:

char baa(int x) {
    static char foo[] = " .. ";
    return foo[x ..];
}

instead of:

char baa(int x) {
    char foo[] = " .. ";
    return foo[x ..];
}

It seems to be very common on Linux source codes applications. Is there any performance difference? If yes, might someone explain why? Thanks in advance.

Answer 1

It’s not for performance per se, but rather to decrease memory usage. There is a performance boost, but it’s not (usually) the primary reason you’d see code like that.

Variables in a function are allocated on the stack, they’ll be reserved and removed each time the function is called, and importantly, they will count towards the stack size limit which is a serious constraint on many embedded and resource-constrained platforms.

However, static variables are stored in either the .BSS or .DATA segment (non-explicitly-initialized static variables will go to .BSS, statically-initialized static variables will go to .DATA), off the stack. The compiler can also take advantage of this to perform certain optimizations.