Dark Horse Programmer ——— Learn some notes of C language

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Static and extern

external functions : Defined functions can be accessed by this file and other files

intrinsic functions : Defined functions can only be accessed by this file and other files cannot be accessed

By default, all functions are external functions.

A complete definition of an external function:

Extem viod Test ()//extern can be omitted, default is omitted

{
printf ("Call the test function \ n")
}

Complete declaration of an external function:

Extem viod test (); You can omit extern, which is an external function by default

Define an intrinsic function:

Static Viod Test2 ()
{
printf ("Call test2")
}

Intrinsic functions cannot be accessed directly by other files, but can only be accessed indirectly

External functions with the same name are not allowed, and the names of intrinsic functions do not conflict within each file.

Static effects on functions:

1. Define an intrinsic function

2. Declaring intrinsic functions
The effect of extern on functions:

1. Complete definition of an external function

2. Complete declaration of an external function

static and extern effects on variables: defining and declaring an internal and external variable

External variables: Defined variables can be accessed by this file and other files
Internal variables: Defined variables can only be accessed by the file and cannot be accessed by other files

By default, all global variables are external variables
External variables of the same name in different files represent the same variable and can be defined repeatedly

Function

Any C language program is composed of one or more program segments, each of which has its own function, we generally call these program segments as functions, so you can say that the C language program is composed of functions.

Definition of a function

1. Purpose of defining functions
Encapsulates a common feature to facilitate later invocation

2. Steps to define a function

Function name: What are the names of functions?
Function Body: What is the function and what code it contains

3. Format

Fixed format (This is the case for many language functions)

return value type function name (formal parameter list)

{
function body

}

Example

Defines a function that calculates the number of two integers and

sum (int a, int b)
{
int c =a+b;

}

Formal parameters and arguments

Parameters: variables to be defined when a function is defined, parameters can have countless variables that cannot be defined in a function body and parameters

Arguments: The actual parameters of the function are passed in when the function is called, and the argument must correspond to the parameter one by one

Attention

If the base data type is a function parameter, it is purely a value pass, modifying the value of a function's internal parameter without affecting the value of the outer argument

A function can have no formal parameter, or it can have an infinite number of arguments

Define an internal variable:

static int b; and define the form of an intrinsic function almost

Internal variables of the same name in different files, not affecting each other

Dark Horse Programmer ——— Learn some notes of C language