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Function call with large structure.

Started by davidkosenina Jan 20, 2005 at 5:28 PM 3 replies 650+ views

Original Post

Jan 20, 2005 at 5:28 PM

If i have very large structure and i pass it into a function as a parameter, does the compiler optimize this or does it pass all struct members on the stack? It is better to use pointers or references in terms of speed right? I was looking at some source code and i was wondering if it yust wasnt optimized or is this some "advanced stuff". Tnx.

C-Junkie

139

C-Junkie

Jan 20, 2005 at 5:43 PM

It can't.

NOT passing it on the stack would mean the pass-by-value versus pass-by-reference semantics get messed up. That can't happen. (at least, I'm pretty sure C and C++ don't suddenly change how they work in the face of structures, unlike, say, java?)

Change the function to use a pointer or reference.

Anon Mike

117

Anon Mike

Jan 20, 2005 at 6:42 PM

Typically in these cases you pass the struct by const reference (for C++).

foo(const BigStruct & stuff);

It looks the same at the call site (e.g. foo(stuff)) but doesn't have the copying.

CGameProgrammer

179

CGameProgrammer

Jan 20, 2005 at 6:57 PM

References are implicit pointers -- the generated output is identical to what it would be using pointers, but the C++ code is much cleaner. So use those. And you don't really need to make it a const as Anon Mike suggested... but you can.

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