Memory model, reference and function supplement of program

Partition model of memory

c++ When the program executes, the memory is roughly divided into 4 Regions

1. Code section ： Store the binary code of the function body , Managed by the operating system
2. Global area ： Store global and static variables and constants
3. The stack area ： Release is automatically allocated by the compiler , Stores the parameter values of the function , Local variables, etc
4. Heap area ： Assigned and released by the programmer , If programmers don't release , Recycle by the operating system at the end of the program

After the program is compiled , The first section that generates the execution of the program is divided into two areas

Code section ：

Deposit CPU Machine instructions executed
The code area is shared , The purpose of sharing is for programs that are frequently executed , Just have a copy of the code in memory
The code area is read-only , The reason to make it read-only is to prevent the program from accidentally modifying its instructions

Global area ：

Global variables and static variables are stored here
The global area also contains a constant area , Character constants and other constants are also stored here
The data in this area is released by the operating system at the end of the program

Heap area ：

Heap data is managed and released by programmers
Heap data utilization new Keyword to open up memory

new The operator

The heap area opens up a number , It's the address , Receive... With a pointer
Example

int *p = new int(10) // In parentheses are numbers 

The heap opens up an array , It's the address , Receive... With a pointer
Example

int *arr = new int[10] // In parentheses is the array size 

After that, the access is normal ,arr Equivalent to array name

For releasing data delete, Where the array is released with delete[] arr

quote

You can alias variables , Use aliases to manipulate variables
grammar ： data type & Alias = Original name
for example ：
int a = 10
int &b = a

You can use it b To operate a The numerical

matters needing attention

• References must be initialized
• Reference after initialization , Can't change

Three kinds of transmission

Value passed , Parameter changes do not affect arguments

void fun(int a, int b)
fun(a,b)

Address delivery , Parameter changes affect arguments

void fun(int *a, int *b)
fun(&a, &b)

reference , Parameter changes affect arguments

void fun(int &a, int &b)
fun(a,b)

Reference as function return value

effect ： A reference can exist as the return value of a function

Be careful ： Do not return local variable references

usage ： Function calls can be used as lvalues
for example

int& test(){
    
	static int a = 20;
	return a;
}


test() = 1000;// It is equivalent to modifying the contents of the returned reference 

The essence of quotation

The essence of quotation is c++ The internal implementation is a pointer constant

const reference

int& ref = 10;// This is wrong , The reference itself needs a legal memory space 
const int& ref = 10 That's right , The reason is that the compiler optimizes the code 
 It's equivalent to executing  int temp = 10; const int& ref = temp;

effect ： Constant references are mainly used to modify formal parameters , Prevent misoperation

In the function parameter list , You can add const Modified parameter , Prevent formal parameters from changing arguments

Function addition

Function default parameter considerations ：

1、 If a location parameter has a default value , All parameters from this position must have default values
2、 If the function declaration has default arguments , Function implementations cannot have default parameters , Only one declaration and implementation can have default parameters

function overloading ：

1、 The same scope
2、 The function names are the same
3、 Function parameter types are different , Or different numbers , Or in a different order
4、 The default parameter will be ambiguous , Report errors , To avoid