Start from scratch-06. preprocessing directives in C language

preprocessing directives

• Macro definition with no parameters:

Format: #define Macro Name Value

Function: Improve the readability of code

The value after the macro name is replaced by all occurrences where the macro name is marked before the program is compiled

• macro definition with Parameters

Format #define Macro name (parameter list) parameter expression

Function: Before compiling, replace all occurrences of the macro name (x) with the parameter representation

When I write a macro definition with parameters, I need to use () to amplify each parameter and result.

• Conditional compilation:

Format: #if #elif #else #endif

Function: A statement that compiles a condition when it is satisfied

Note point: Conditional compilation must end with #endif

• file contains

#include: Copy the contents of the file behind the include to # include

#include "" To include your own writing file

#include <> to include system-supplied header files