One 、 Memory

 1. Memory unit

   In order to use memory effectively , Divide the memory into small ones Memory unit ; In order to effectively access each unit , The memory unit is numbered , These numbers are called The address of the memory unit .

 2. Memory address

   What we often say 32 Bit and 64 Position refers to 32 or 64 Root address line , The address line is a physical line , It's actually a wire that can be energized , The positive charge is 1 Negatively charged 0;
   Convert electrical signals into digital information , You can get a set of 0、1 Binary number of components ;
   stay 32 In the middle of the plane , We put 32 All the electrical signals generated by the root address line are listed , You can get 2³² Group binary number , We call these binary numbers memory numbers , And these binary numbers are what we call Memory address ;

   Each address corresponds to a memory unit , The size of a memory unit is one byte .

Two 、 The pointer

 1. Pointer to the variable

   The address number of memory is actually a value , You also need space to store , Pointer variables are used to store address numbers , Simply put, a pointer is an address .
   Pointers are typed , The way we declare a pointer variable is data type * Pointer name , among data type It explains what type of object this pointer executes ,* This indicates that this is a pointer variable .

int main() {
    
	//a Space is allocated in memory  - 4 byte 
	int a = 10;
	// Define a pointer variable pa, And will a Address assigned to pa
	//* explain pa It's a pointer variable 
	//int  explain pa The object of execution is int Type of 
	int* pa = &a;
	//& It's a monocular operator , Used to get the address 
	//%p Specifically for printing addresses 
	printf("a The address is %p\n", &a);
	//* Dereference operation , *pa It is through pa Address inside , find a
	*pa = 20;
	printf("a Value ：%d", a);
	return 0;
}

 1. Pointer size

   We said that the pointer is the address , And the essence of address is a value , Then this value also needs to be stored , In other words, pointer variables also need memory space to store , How big is a pointer ？

// Pointer size 
int main() {
    
	printf("%d\n", sizeof(int*));//4
	printf("%d\n", sizeof(char*));//4
	printf("%d\n", sizeof(long*));//4
	printf("%d\n", sizeof(long long*));//4
	printf("%d\n", sizeof(double*));//4
	printf("%d\n", sizeof(float*));//4
	printf("%d\n", sizeof(short*));//4
}

   How much space does the pointer occupy , It depends on how much space is needed to store the address , And the address is actually a string of binary numbers , So no matter what type of pointer , It's the same size ;
   How big is the pointer ？ In fact, it's not hard to get out , The length of each binary number is actually determined by the number of address lines ,32 The address line of the bit machine has 32 root , Each address line corresponds to a binary number , therefore 32 The binary number length of bit machine is 32, be 32 The size of the bit machine pointer is 4 byte . Empathy ,64 Bit machines are 8 Bytes .

  【 Learning notes Dog learn C】 Initial order of pointer
  【 Learning notes Dog learn C】 Advanced pointer