How to use in C preprocessing instructions

In C, all preprocessing commands start with a " " sign.

The concept of preprocessing in C programming: processing before compilation. There are three main aspects of preprocessing in C: macro definition and failing.

File contains, conditional compilation.

In C, preprocessor directives are used to perform specific operations before compiling, such as defining constants, judging conditions, including files, and so on. Here are all the preprocessing instructions in C

define: Defines a constant that can be used in **.

undef: Undefines a constant.

if, else, elif, endif: used for conditional compilation, and different ** blocks are compiled according to the conditions next to the cherry search.

warning, error: Used to issue compilation warnings or errors.

line: used to modify the compiler line number.

region, endregion: Contains the **block in a region**, which is convenient for folding and management**.

pragma: Used to modify the behavior of the compiler.

nullable: Used to control the behavior of nullable reference types.

nullable enable: Enables nullable reference types.

nullable disable: disables nullable reference types.

nullable restore: restores the state of a nullable reference type.

No, not all, but the preprocessing command must start with .

Preprocessing simply means copying that library function into your program.

That's right. Preprocessing, or precompilation, refers to the work done before the first scan of the compilation (lexical scanning and syntax analysis). Preprocessing instructions indicate what the compiler is doing before the program is officially compiled, and can be placed anywhere in the program.

Preprocessing is an important feature of the C language, and it is done by the preprocessor. When compiling a source file, the system will automatically reference the preprocessor to process the preprocessing part of the source program, and automatically enter the compilation of the source program after processing.

The C language provides a variety of preprocessing functions, mainly dealing with the precompilation instructions at the beginning, such as macro definition (define), file inclusion (include), conditional compilation (ifdef), etc. The program written by the reasonable use of the preprocessing function is easy to read, modify, transplant and debug, and is also conducive to modular program design.

The result of the preprocessor is handed over to the compiler.