1. memory partition model

C++ Program in execution , The main direction of memory is 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 .

The meaning of four memory areas ： Data stored in different areas , Give different life cycles , Give us greater flexibility in programming .

1.1 Before the program runs

After the program is compiled , Generated exe Executable program , Before the program is executed, it is divided into two areas .

Code section ：

1. Deposit CPU Machine instructions executed .
2. 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 .
3. 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 ：

1. Global variables and static variables are stored here .
2. The global area also includes the constant area , String constants and other constants are also stored here .
3. The data in this area is released by the operating system at the end of the program .

Not in the global area	In the global area
local variable	Global variables ; Static variables ：static keyword
const Modified local variables （ Local constants ）	Constant ： String constant ;const Decorated global variables （ Global constants ）

Example ：

#include<iostream>
using namespace std;

//  Create global variables 
int g_a=10; 

int main()
{
    
	//  Global area ： Global variables , Static variables , Constant 
	
	//  Create ordinary local variables 
	int a=10;
	
	//  Static variables   Add... Before ordinary variables static, It's a static variable 
	static int s_a=10;
	
	//  Constant ： String constant  const Decorated global variables  
	
	system("pause");
	return 0;
}

1.2 After program running

The stack area ：

1. Release is automatically allocated by the compiler , Stores the parameter values of the function , Local variables, etc .
2. matters needing attention ： Do not return the address of a local variable , The data opened in the stack area is automatically released by the compiler .

Example ：

#include<iostream>
using namespace std;

int* func()
{
    
	int a=10;			//  local variable , Store in the stack area , The data in the stack area is automatically released after the function is executed 
	return &a;			//  Returns the address of a local variable  
}

int main()
{
    
	//  Accept func The return value of the function 
	int* p = func();
	
	cout<<*p<<endl; 		//  You can print the right numbers for the first time , It's because the compiler has reserved  
	//cout<<*p<<endl; //  The second time, the data is no longer kept  
	
	system("pause");
	return 0;
}

Heap area ：

1. Release is assigned by the programmer , If programmers don't release , Recycle by the operating system at the end of the program .
2. stay C++ The main use of new Open up memory in the heap .

Example ：

#include<iostream>
using namespace std;

int* func()
{
    
	//  utilize new keyword   Data can be opened up to the heap 
	int* p = new int;
	*p=10;
	return p; 
}

int main()
{
    
	//  Open up data in the heap 
	int* p = func();
	cout<<*p<<endl;
	cout<<*p<<endl; 
	system("pause");
	return 0;
}

1.3 new The operator

C++ In the use of new The operator creates data in the heap .

Data from the development of the reactor area , It's created manually by the programmer , Hand release , Release utilization operator delete.

grammar ：new data type

utilize new Data created , Will return a pointer to the type corresponding to the data .

Example ：

#include<iostream>
using namespace std;

//  Utilization in the reactor area new Open up arrays 
void test02()
{
    
	//  establish 10 An array of integer data , In the pile area 
	int* arr=new int[10];
	for(int i=0; i<10; i++)
	{
    
		arr[i] = i+100;	
	}	
	for(int j=0; j<10; j++)
	{
    
		cout<<arr[j]<<endl; 
	}
	
	//  Free heap array 
	//  When releasing the array , To add [] Can only be 
	delete []arr; 
} 

int main()
{
    
	test02();
	
	system("pause");
	return 0;
}