Small details of the use of macro definitions in C language _c language

#pragma #pragma preprocessing instructions
In all preprocessing instructions, the #Pragma instruction may be the most complex, and its role is to set the state of the compiler or instruct the compiler to perform certain actions. #pragma指令对每个编译器给出了一个方法, to give the host or operating system proprietary features, while maintaining complete compatibility with the C and C + + languages. By definition, the compilation instructions are proprietary to the machine or operating system and are different for each compiler.
The format is generally: #Pragma Para
... etc..... etc..

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Two ways to enforce the use of a function instead of a macro definition:

1: #undef Isalpha

Appears before Isalpha () and still contains <ctype.h> at the top of the file; You can force the compiler to use a function definition.

2: (Isalpha) (c)

The preprocessor does not think of this structure as a macro, but as a function call