Pointer vs. Reference


Question

What would be better practice when giving a function the original variable to work with:

unsigned long x = 4;

void func1(unsigned long& val) {
     val = 5;            
}
func1(x);

or:

void func2(unsigned long* val) {
     *val = 5;
}
func2(&x);

IOW: Is there any reason to pick one over another?

1
247
4/27/2015 6:43:59 PM

Accepted Answer

My rule of thumb is:

Use pointers if you want to do pointer arithmetic with them (e.g. incrementing the pointer address to step through an array) or if you ever have to pass a NULL-pointer.

Use references otherwise.

275
7/31/2014 12:11:49 AM

I really think you will benefit from establishing the following function calling coding guidelines:

  1. As in all other places, always be const-correct.

    • Note: This means, among other things, that only out-values (see item 3) and values passed by value (see item 4) can lack the const specifier.
  2. Only pass a value by pointer if the value 0/NULL is a valid input in the current context.

    • Rationale 1: As a caller, you see that whatever you pass in must be in a usable state.

    • Rationale 2: As called, you know that whatever comes in is in a usable state. Hence, no NULL-check or error handling needs to be done for that value.

    • Rationale 3: Rationales 1 and 2 will be compiler enforced. Always catch errors at compile time if you can.

  3. If a function argument is an out-value, then pass it by reference.

    • Rationale: We don't want to break item 2...
  4. Choose "pass by value" over "pass by const reference" only if the value is a POD (Plain old Datastructure) or small enough (memory-wise) or in other ways cheap enough (time-wise) to copy.

    • Rationale: Avoid unnecessary copies.
    • Note: small enough and cheap enough are not absolute measurables.

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