Help with cpp pointers and references and const

[alamahant]

Hello Guys,
For the last two months I have been playing around a bit with cpp and although I understand a bit the meaning of pointers and references and constants when I see some real world code I get overwhelmed by the cataclysm of them.
It is as if nobody hardly ever uses plain variables.
Most methods use const references for their parameters.
I feel extremely confused.
How can one get the grip of these things?
How did you do it?
Thanks for bearing with my ignorance and any advise would be super...
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[logrusx]

[pingtoo]

May I suggest give us examples so it will be easier to understand your point.

It will be better if you can give a cpp example the illustrate the point you made about current practice the confuse you and a second example that you believe will do that same as first example but use your idea of variables so we have a contrast that will help understand where your key confuse.

[GDH-gentoo]

One important use of references is avoiding duplication of objects that might be expensive to duplicate. And doing a "move" instead of a copy when possible. Think objects of classes that have constructors and destructors that do a nontrivial amount of work. Simple objects of scalar type are not that expensive to copy, so code usually bothers less with references to those types.

When you "use plain variables", as you put it, there can be a lot of that duplication without you realizing it.

C code sometimes uses pointers to structure types for similar purposes, to avoid creating unnecessary copies of objects of those types.

And when pointers or references are used, specifying const makes the compiler yell at you if you inadvertently attempt to modify the object through the pointer or reference in code that is not supposed to, as logrusx said. And that is good for avoiding bugs.

Posting an example that uses references where you would be inclined to "use plain variables", as pingtoo suggests, might help us better explain this idea to you.
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[Genone]

The main reason to use const references instead of regular variables is to avoid data transfers. For scalar variables it doesn't really matter, but for more complex data types it avoids unnecessary copying and potentially expensive construction of temporary variables. In practice it shouldn't really matter to you when calling a function/method wether the parameter is a const reference or a plain copy-by-value parameter as they both accept r-values. Mind that does not apply to non-const references, those are usually used for in-out parameters in C++ (while C usually uses pointers in that case) which restricts any inputs to l-values.

(if you don't know what r-value and l-value mean you really should look it up).

[SiberianSniper]

One other thing to mention is the difference between passing pointers vs. references. Once compiled, the machine code will usually be identical, so you may wonder when to use each one in favor of the other In general, using a pointer signifies that the object may or may not exist (so you need to check for nullptr), whereas a reference means that the object does exist (unless you're intentionally doing stupid language tricks).

Also, raw pointers are effectively deprecated for *most* purposes, so you may want to look into the C++11 smart pointers (unique_ptr, shared_ptr, and weak_ptr).