In C, does using static variables in a function make it faster?

My function will be called thousands of times. If i want to make it faster, will changing the local function variables to static be of any use? My logic behind this is that, because static variables are persistent between function calls, they are allocated only the first time, and thus, every subsequent call will not allocate memory for them and will become faster, because the memory allocation step is not done.

Also, if the above is true, then would using global variables instead of parameters be faster to pass information to the function every time it is called? i think space for parameters is also allocated on every function call, to allow for recursion (that's why recursion uses up more memory), but since my function is not recursive, and if my reasoning is correct, then taking off parameters will in theory make it faster.

I know these things I want to do are horrible programming habits, but please, tell me if it is wise. I am going to try it anyway but please give me your opinion.

Edit Report

The best way to find out is to actually run a profiler. This can be as simple as executing several timed tests using both methods and then averaging out the results and comparing, or you may consider a full-blown profiling tool which attaches itself to a process and graphs out memory use over time and execution speed.

Do not perform random micro code-tuning because you have a gut feeling it will be faster. Compilers all have slightly different implementations of things and what is true on one compiler on one environment may be false on another configuration.

To tackle that comment about fewer parameters: the process of "inlining" functions essentially removes the overhead related to calling a function. Chances are a small function will be automatically in-lined by the compiler, but you can suggest a function be inlined as well.

In a different language, C++, the new standard coming out supports perfect forwarding, and perfect move semantics with rvalue references which removes the need for temporaries in certain cases which can reduce the cost of calling a function.

I suspect you're prematurely optimizing, however, you should not be this concerned with performance until you've discovered your real bottlenecks.

answered 2010-10-01T01:06:34.990

In C, does using static variables in a function make it faster?

1 Answer

Your Answer