i have searched adn read something about all but i couldnt underestand at last.
please explain those simply
Not much or a lot depending on which one you choose:-
A library is just one module .Dll .a .so .lib either static or dynamic that you can link with.
An SDK will usually contain lots of libraries and the headers that describe the types on the library interfaces, but some sneaky people might call this a code library or library for short which is confusing.
A toolkit could be anything from 1 library + 1 header to a whole SDK plus compiler, linker, editor, resource compiler, idl compiler and a sack load of tools like debuggers, introspectors and crash dump analysers. Sometime you get all that and they still just call it a Software Development Kit as that's what it is.
Library: It is a collection of methods/functions wrapped up into a package that can be imported into a code project and re-used.
Toolkit: It is a group of tools (and at times code libraries) that you can use to make it easier to access a device or a system.
SDK: Software Development Kit is a set of libraries that help you in developing code that uses a particular system.
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