Passing structures as function arguments versus pointers to structures

[bmihura]

Does CVI copy the entire C structure when you pass it directly instead of passing a pointer to it?

[LuisG]

Yes, indeed.

Luis
NI

[cdk52]

It is almost always better to pass a pointer to your struct. Keep in mind:

• By passing a pointer, you avoid the overhead of pushing the entire contents of the struct onto the stack, then popping it in your called function. This is especially a problem when dealing with large structs.
• If your function needs to modify any member of the struct, you have no choice: you must pass a pointer.

Regards,

Colin.

[menchar]

ANSI C (C89) provides ONLY call by value parameter passing, but that value can be a pointer 🙂  Array parameters are converted to pointers, and the pointer is then passed by value.

A struct is passed by value (not automatically converted to a pointer value), and you can of course modify such a struct in the called routine.  The issue is whether you intend changes to the struct made in the called routine to occur in the actual parameter (pointer to struct used as parameter value and explicitly dereferenced)  or in the local copy of a struct passed as a parameter.

[bmihura]

Thanks all, I suspected as much.

I have seen C compilers break the ANSI rule and pass a pointer when the function argument wasn't.

[bmihura]

My reply appeared earlier in the thread, thanks all.