Better understanding the STL

[keanedawg]

Alright, so this is a topic where I have very little exposure. So I feel like I need some sort of guidance to understand it all.

This has happened to me more than once. I will sometimes follow the breakpoints in visual studio which eventually lead me to STL code. For example, this is code from Math.h

_Check_return_ _ACRTIMP short __cdecl _dclass(_In_ double _X);
_Check_return_ _ACRTIMP short __cdecl _ldclass(_In_ long double _X);
_Check_return_ _ACRTIMP short __cdecl _fdclass(_In_ float _X);

I don't know what it does, but the part that bothers me most is how unusual the syntax is.

For example, what does "_In_" do and why do they care to surround every input parameter with it? I never do that with my code.

Moreover, what are these functions even returning? I see like 3 or 4 variables or keywords that I've never seen before: "_Check_return_, _ACRTIMP, __cdecl"? Plus, why is the short there?

[Cubbi]

I never do that with my code.

And you shouldn't. In C++, anything that has two underscores in a row (__cdecl) and anything tha tbegins with an underscore followed by a capital (_Check_return_, _ACRTIMP, _In_) are symbols reserved for use by the internals of the standard library, for their internal purposes. (see http://en.cppreference.com/w/cpp/language/identifiers#In_declarations )

Here you see a few different internal Microsoft-only things

_Check_return_ and _In_ are part of The Microsoft source-code annotation language.

_Check_return_ is documented here: https://msdn.microsoft.com/en-us/library/jj159529.aspx

_In_ is documented here https://msdn.microsoft.com/en-us/library/hh916382.aspx

__cdecl is the venerable old Microsoft keyword for the C calling convention, documented here: https://msdn.microsoft.com/en-us/library/zkwh89ks.aspx

_ACRTIMP is a macro, your compiler should tell you what it is

Plus, why is the short there?

it's the return type of the three functions being declared

[Moschops]

At this stage, I suspect you won't get much understanding of the STL by trying to figure out how other people have implemented it.

Start with learning how to use the basic containers; what they're for, what you can do with them. Start with vector.