performance - c++ How to be efficient with my function use? -

i'm running simulation takes time run , want improve that. understood, passing value function means that value copied slow. there way include functions in dedicated file won't need copy values?

i don't mind "wrong programing" (global variable, public access etc.) gain speed.

thanks

edit: when started project, tested several loops. counted processor style between start , stop of loop of kind:

int = 0; while (i < 10000000){   = dostuff(i); //or dostuff(); }  int dostuff(i){   return i++; }  int dostuff(){   return i++; } 

i'm pretty sure dostuff() case 10 times faster. have changed previous code global variables , direct access ("wrong programming") , improved runtime significantly. tried use references had inherent problem prevented me doing (i don't remember was). anyhow, i'm playing around gprof now.

you use references. if have function:

void examine(bighairyobject o) {     cout << o.data[1234]; /* example */ } 

you can avoid copy passing reference object:

void examine(bighairyobject & o) {     cout << o.data[1234]; /* use identical */ } 

the downside of this, referring original object, not copy of it. so, if modify o (in example), modifying caller's object.

if want promise not modify object (and in case, reference copy), use const keyword:

void examine(const bighairyobject & o) {     cout << o.data[1234]; /* use identical */     // o.data[1234] = 5; // cause compile error. }