Re: efficiency in passing a value to a function

[Shriramana Sharma <samjnaa@gmail.com>]

Steve Graegert wrote:

> I have seen many programs making use const reference parameters in
> order to inform the compiler that the parameter is read-only, and
> hence should be better optimized.

I thought the usage of const before & in function definitions was to 
prevent the value from being modified. I never knew there is an 
optimization aspect.

> Unfortunately, this intent is at odds with the C++ language
> definition. The const keyword says that the storage may not be
> modified through the given name. What it does not say is that the
> storage cannot be modified through some other name.

I observe that this is true for C too, not just C++. Anyway, how is it 
exactly "at odds" with the language definition?

[BTW gcc is intelligent enough to give me a compile-time warning:

const.c:7: warning: initialization discards qualifiers from pointer 
target type

when I write const int i = 2 ; int * iptr = & i ; and I don't even have 
to give -Wall !]

> you can only initialize them, const is basically ineffective a
> improving run-time performance. It does, however, catch errors in the
> programming process.

const is also useful for preventing a function writing to a variable 
passed to it as reference, which is what this thread was originally about.

Just for the record, are there any other uses for const?

Shriramana Sharma.