Small details of macro definition in C Language

# Pragma preprocessing instructions
Among all the pre-processing commands, the # Pragma command may be the most complex. It is used to set the compiler status or to instruct the compiler to complete some specific actions. # The pragma command provides a method for each compiler to provide the unique features of the host or operating system while maintaining full compatibility with C and C ++ languages. According to the definition, the compilation instructions are proprietary to machines or operating systems and are different for each compiler.
The format is generally: # Pragma Para
...... Etc ..

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Two methods to force the use of functions rather than macro definition:

1: # undef isalpha

It appears before isalpha () and still contains <ctype. h> at the top of the file. You can force the compiler to use function definitions.

2: (isalpha) (c)

The pre-processor does not regard this structure as a macro, but as a function call.