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Which is better for performance when calling a function that provides a simple datatype -- having it fill in a memory location (passed by pointer) or having it return the simple data?
I've oversimplified the example returning a static value of 5 here, but assume the lookup/functionality that determines the return value would be dynamic in real life...
Conventional logic would tell me the first approach is quicker since we are operating by reference instead of having to return a copy as in the 2nd approach... But, I'd like others' opinions.
Thanks
void func(int *a) {
*a = 5;
}
or...
int func() {
return 5;
}
688
Returning the object should be used in most cases because of an optimsation called copy elision. However, depending on how your function is intended to be used, it may be better to pass the object by reference.
Pass-by-references is more efficient than pass-by-value, because it does not copy the arguments. The formal parameter is an alias for the argument. When the called function read or write the formal parameter, it is actually read or write the argument itself.
Pass by value - The function copies the variable and works with a copy (so it doesn't change anything in the original variable) Pass by reference - The function uses the original variable. If you change the variable in the other function, it changes in the original variable too.
Pass by reference (also called pass by address) means to pass the reference of an argument in the calling function to the corresponding formal parameter of the called function so that a copy of the address of the actual parameter is made in memory, i.e. the caller and the callee use the same variable for the parameter.
In general, if your function acts like a function (that is, returning a single logical value), then it's probably best to use int func(). Even if the return value is a complex C++ object, there's a common optimisation called Return Value Optimisation that avoids unnecessary object copying and makes the two forms roughly equivalent in runtime performance.
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