c++ - C语言的语法问题,求大神帮忙?

Answer 1

I have replied to a similar one before, take a look here:
Solving the main function in C language

Simply speaking, P2 is a macro. This macro is for compatibility with older versions of compilers. For details, please see this post I answered.

Answer 2

Isn’t this function overloading?

Answer 3

int_string_copy should be the name of the overloaded function. P1 and P2 are probably macros. For example:

#define P1(type, var) (type var)