During the execution of C + + program, the general direction of memory is divided into four areas

• Code area: it stores the binary code of the function body and is managed by the operating system
• Global area: stores global variables, static variables and constants
• Stack area: automatically allocated and released by the compiler to store function parameter values, local variables, etc
• Heap area: it is allocated and released by the programmer. If the programmer does not release it, it will be recycled by the operating system at the end of the program

1.1 before program operation

After the program is compiled, an exe executable program is generated. Before the program is executed, it is divided into two areas

Code area:

Store machine instructions executed by CPU

The code area is shared. The purpose of sharing is to have only one code in memory for frequently executed programs

The code area is read-only because it prevents the program from accidentally modifying its instructions

Global area:

Global and static variables are stored here

The global area also contains a constant area, where string constants and other constants are also stored

The data in this area is released by the operating system at the end of the program

//global variable
int g_a = 10;int g_b = 10;​
//Global constant
const int c_g_a = 10;const int c_g_b = 10;

​int main() 
{​    

//local variable    
int a = 10;    int b = 10;​    
//Print address    
cout << "local variable a The address is: " << (int)&a << endl;    
cout << "local variable b The address is: " << (int)&b << endl;​    
cout << "global variable g_a The address is: " <<  (int)&g_a << endl;    cout << "global variable g_b The address is: " <<  (int)&g_b << endl;​    //Static variable    
static int s_a = 10;    
static int s_b = 10;​    
cout << "Static variable s_a The address is: " << (int)&s_a << endl;    cout << "Static variable s_b The address is: " << (int)&s_b << endl;​    cout << "The string constant address is: " << (int)&"hello world" << endl;    
cout << "The string constant address is: " << (int)&"hello world1" << endl;​    
cout << "Global constant c_g_a The address is: " << (int)&c_g_a << endl;    cout << "Global constant c_g_b The address is: " << (int)&c_g_b << endl;​    const int c_l_a = 10;   
const int c_l_b = 10;    
cout << "Local constant c_l_a The address is: " << (int)&c_l_a << endl;    cout << "Local constant c_l_b The address is: " << (int)&c_l_b << endl;​    
system("pause");​    
return 0;
}

Summary:

• In C + +, the program is divided into global area and code area before running
• The code area is characterized by sharing and read-only
• Global variables, static variables and constants are stored in the global area
• The global constants and string constants decorated with const are stored in the constant area

1.2 after program operation

Stack area:

It is automatically allocated and released by the compiler to store the parameter values and local variables of the function

Note: do not return the address of local variables. The data opened up in the stack area is automatically released by the compiler

int * func()
{
	int a = 10;
	return &a;
}

int main() {

	int *p = func();

	cout << *p << endl;
	cout << *p << endl;

	system("pause");

	return 0;
}

Stacking area:

It is allocated and released by the programmer. If the programmer does not release it, it will be recycled by the operating system at the end of the program

In C + +, new is mainly used to open up memory in heap area

int* func()
{
	int* a = new int(10);
	return a;
}

int main() {

	int *p = func();

	cout << *p << endl;
	cout << *p << endl;
    
	system("pause");

	return 0;
}

Summary:

Heap data is managed and released by programmers

Heap data uses the new keyword to open up memory

1.3 new operator

Using new operator in C + + to open up data in heap

The data developed in the heap area is manually developed by the programmer, manually released, and released by using the operator delete

Syntax: new data type

For the data created with new, the pointer of the type corresponding to the data will be returned

Example 1: basic syntax

int* func()
{
	int* a = new int(10);
	return a;
}

int main() {

	int *p = func();

	cout << *p << endl;
	cout << *p << endl;

	//Using delete to release heap data
	delete p;

	//cout << *p << endl; // An error is reported. The free space is inaccessible

	system("pause");

	return 0;
}

Example 2: array

//Heap array
int main() {

	int* arr = new int[10];

	for (int i = 0; i < 10; i++)
	{
		arr[i] = i + 100;
	}

	for (int i = 0; i < 10; i++)
	{
		cout << arr[i] << endl;
	}
	//Release array delete followed by []
	delete[] arr;

	system("pause");

	return 0;
}