Dark Horse Programmer-C Learning Note-compiling pre-processing instructions

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A Compiling pre-processing directives

Run , compile-and- link , source code, compile preprocessing

Compile pre-processing directives: parsing instructions before compiling

Feature: All compilation preprocessing directives start with #

All compilation preprocessing directives do not have semicolons

Two Macro definition

1. macro definition without parameters: #define Macro Name Value

(1) where the macro name is identified at the time of precompilation, the value following the macro name will be replaced

Note: Macro names in comments are not replaced

The macro name that appears in the string is not replaced

(2) Naming conventions for macro names: All caps, with multiple words separated by underscores

2. macro definition with parameters: #define Macro name ( argument list ) expression

(1) The parameters in the argument list are substituted into the expression, and then replace the place where the macro name appears

Note: There is no data type in the parameter list.

Do not add a space between the macro name and the parentheses

(2) The difference between a macro definition with a parameter and a function:

function has the call process, will open up storage space, the cost is larger

The macro is just a replacement operation

(3) To cancel the definition of a macro #undef

Own understanding of:

1. When doing a problem, remember that the macro is just a replacement operation

2. When you define a macro, enclose all occurrences of the parameter and the result of the operation.

3. Do not use the self-increment and compound assignment operators in parameters

Three Conditional compilation: Compile a piece of code when the condition is met at compile time

1. format: #if start #elif #else #endif End

Features: (1) Conditional compilation conditions can only be made up of macro definitions and constants, cannot appear variable

(2) Judgment at compile time

Usage scenarios:

1. #indef Macro Name

If a macro is defined, execute the statement here

#endif

2. #ifndef

If you do not define a macro, execute the statement here

#endif

Four. Static and extern

1. The role of local variables

Static: (1) extends the life cycle of a variable: from the start of the first execution until the file exits

(2) The defined line of code executes only once

(3) does not change the scope of the variable

extern: placed inside a function, just a declaration of a global variable

2. The role of global variables

Internal variables: Variables that can only be accessed in this file

External variables: Variables that can be accessed in all files

Static: Declares or defines an internal variable

extern: Declaring or defining an external variable

3. Effects on functions

Intrinsic functions: Functions that can only be used in this file

External functions: Functions that can be used in other files, by default all functions are external functions

Static: Declares or defines an intrinsic function

extern: Complete declaration or definition of an external function

Dark Horse Programmer-C Learning Note-compiling pre-processing instructions