Quote:
There appears to be application specific API's and operating system API's. Is this correct?
Yes.
Quote:
Are win32 API's classes in a language such as C#
What do you mean?
Win32 API
are
functions packaged in (several)
DLL
s.
Quote:
If an APi can be set up as a DLL or even a Windows Service can they utilise operating system functions?
Yes, an
API
can internally use other
API
s, in fact an
API
can use whatever is available.
Quote:
API's also seemed to be provided with an application provided by a third party but I am correct in assuming these are limited to exposing and using functionality of the third party application?
The very purpose of an
API
is exposing functionality.
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I am interested in learning how to create APi's on both Windows and Unix\Linux and wondered if anyone could provide any resouces for learning these.
That's not difficult. Create a bunch of functions (or classes, etc..) make them available (e.g. package them in a dynamic or static library or whatever) and document it. The difficult task is providing a
good API
.