CODEWITHSUNDEEP
ccpython
Aditya
Aditya

Reputation: 1268

Need help deciphering C syntax

I have worked on several projects in college on C, but never used it in professional capacity.

Recently I started reading through cpython's source code and the following syntax confused me: github

What does PyAPI_FUNC(int) PyToken_OneChar(int); the part before the function name mean? Is it a wrapper function that dynamically constructs the return type?

I am not even sure what to Google search for, in this case!

Upvotes: 3

Views: 828

Answers (2)

Caleb
Caleb

Reputation: 125007

PyAPI_FUNC() is a macro defined in pyport.h. The particular definition depends on the platform you're building on, but here's an example:

#define PyAPI_FUNC(RTYPE) __declspec(dllimport) RTYPE

So the line in your question, PyAPI_FUNC(int) PyToken_OneChar(int); expands to:

__declspec(dllimport) int PyToken_OneChar(int);

Basically, it just declares the name PyToken_OneChar as a function that takes an int as its parameter and returns an int, but it does it in a way that lets the compiler embed storage information with those types. See What is __declspec and when do I need to use it? for more information about the __declspec directive if you're interested. Another of the definitions for PyAPI_FUNC is:

#define PyAPI_FUNC(RTYPE) RTYPE

which skips all that and just expands the line above to:

int PyToken_OneChar(int);

So the main thing to take away from this is that source code that's meant to compile on multiple platforms often uses macros that make it easier to write code once and use it on each of those platforms. In this case, it lets the programmers write declarations for PyToken_OneChar() and many other functions once instead of having to write (and maintain!) different versions for each platform. This is fairly advanced stuff -- not something you should worry about if you're getting started.

Upvotes: 6

Keith Nicholas
Keith Nicholas

Reputation: 44306

It's a C Macro they wrote which allows them to do different things on different OS platforms, for instance, on windows, this will export the function as part of the public interface for a DLL.

Upvotes: 4

Related Questions