Mortal immortal cultivation pointer-1

One 、 The goal of the tutorial

Videos for this tutorial  

1. Through the theme of mortal cultivation , Study C/C++ The pointer , From entry to mastery （ Mastery here refers to the mastery of knowledge points ）.
2. In the use of pointers , Meet the technical requirements of enterprise development and written examination .
3. Effect demonstration ： Make it easy FPS Unlimited ammunition and blood lock in shooting games 、 Blinking and other functions .

Two 、 Tutorial preparation

1. Prepare any development environment .gcc, g++, vs, devc++, vscode Wait for any one .

2. Don't know how to cultivate Immortals , You can also master this tutorial without obstacles .

3、 ... and 、 The Syllabus

Four 、 The influence of mortal cultivation on me

One man fixes the immortals , Especially later , There are many slots . But the flaws are not hidden , every last IT people , Can find their own shadow in it . Dark forest law of three bodies , There is no way to disprove , There is no evidence , It's too far away from us . And the jungle law of the jungle in the fairy world , But now you can see , Touches . Every self-study scholar , It's the casual practice without any support , Along the way , All kinds of pits and traps ...

Follow Rock, Let's practice together , To conquer completely C/C++ The pointer , Quickly improve your technical strength ！
 

  5、 ... and 、 Pointer practice period

5.1  Pointer zero foundation quick start

I'm going to the sea of stars , Look for Xiuxian cave , There is exuberant aura , It's just too far away from China , Thousands of miles apart , How can we “ teleport ”？ The immortal world “ Transmission array ”, You deserve it ！

The transmission array is in the cultivation world “ The pointer ”.

5.1.1 Use “ The pointer ” Make your own transmission array

char LuanXingHai; //  A sea of stars ,  There is a lot of aura in the world of cultivating immortals , It is especially suitable for the continent of cultivating immortals .
	
//  Let the sea of stars , Set to H,  The way 1：
LuanXingHai = 'A';
printf("%c\n", LuanXingHai);

//  Suppose we don't have permission directly to  LuanXingHai  Set up the data , You can use the method 2：
// 1.  Record LuanXingHai The address of 
int addr = &LuanXingHai;
// 2.  Make a transmission array , Namely “ The pointer ”
char* p;
// 3.  hold LuanXingHai The address of , Assign a value to the transmission matrix 
p = addr; // Pay attention to C++ Language compiler , You need to cast 
// 4.  Use the transmission array （ The pointer ）, Transmit data 
*p = 'H';

printf("%c\n", LuanXingHai);

  Use pointer transfer matrix , Teleport to the holy land of immortality - A sea of stars .

5.1.2 Transmission array （ The pointer ） In two ways

//  First usage ： Read the data of the designated destination , That is to say “ read ”
char value = *p;

//  Second usage , The data “ transmission ” To the designated destination , That is to say “ Write ”
*p = 'H';

5.1.3  The relationship between pointer and address

Pointer value , It's essentially an address .

The pointer , It is equivalent to a transmission array . This transmission array , You need to go to an immortal or even a destination first , This destination , The destination transmission address is required , That's it “ The pointer ” Value .

5.1.4  The type of pointer

Different types of transmission arrays , The objects that can be transmitted are different , Force transmission , Talk lead “ Space cracks ”, Cause the object to be destroyed .

Different types of pointers , Only certain types of data can be transmitted , Force transmission , It may lead to unexpected consequences such as data damage .

int lingShi = 512; //  Lingshi , A common currency in the celestial world , Equivalent to the gold of secular society 
char * p = &lingShi; //C++ The compiler needs to cast 
*p = 1; 
printf("%d", lingShi); //  In small end format computers , Output  513

Particular attention , stay C++ In the compiler （ The suffix of the file is .cpp By default c++ compiler ）, Different types of pointers are assigned directly , Fail to compile , A cast is required , But in a lot of C In the language compiler , You can assign values directly .

Pointer with mismatched type , Forced access to , May lead to unexpected consequences ！ Similar to that in the immortal world “ Space cracks ”, Very dangerous ！ The ancient Warcraft of the world of Warcraft , Is to invade the human world from the space crack , Lead to death ...

5.1.5  The underlying understanding of pointers

int lingShi = 100; //  Lingshi , A common currency in the celestial world , Equivalent to the gold of secular society 
int * p = &lingShi;

printf("%d", *p); // You need to access memory twice in a row 

5.2  Addition and subtraction of pointers

  Let's go shopping in the black market in the fairy world , Learn the addition and subtraction of pointers by the way .

Pointer plus integer

Stroll the black market , Ask about the price ：

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
//  Go to the black market and ask about the price of monsters 
int* p = &prices[0]; //prices;
printf("%d\n", *p);  //100

p = p + 1; // p++;
printf("%d\n", *p); // 200

p = p + 2;
printf("%d\n", *p); // 800

  Stroll around the black market in small steps , Ask about the price ：

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
char* p2 = &prices[0]; //prices;
printf("%d\n", *p2); // 100

p2 = p2 + 1;  // p++;
printf("%d\n", *p2); // 0

  Cause analysis ：

  Conclusion ： The pointer +1, Point to the next of the pointer “ data ”. If it is char* The pointer , Then advance one byte , The value of the pointer is only added 1. If it is int* The pointer , Then point to the next integer , And an integer is occupied 4 Bytes of , So the value of the pointer , Actually added 4.

p = p + n;   // The pointer p Value , Added   n*sizeof(p The data type of the data pointed to ）

Pointer minus integer

Step back and check the price

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
int* p1 = &prices[1]; //prices;
printf("%d\n", *p1);  //200

p1 = p1 - 1;   
printf("%d\n", *p1); //100

Step back and check the price

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
char* p2 = &prices[1]; //prices;
p2 = p2 - 1; 
printf("%d\n", *p2);  // 0

  Cause analysis ：

 p = p - n;   // The pointer p Value , Less   n*sizeof(p The data type of the data pointed to ）

Pointer minus pointer

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
int* p1 = &prices[0];
int* p2 = &prices[5];
printf("%d\n", p2 - p1); // 5

char* p3 = &prices[0];
char* p4 = &prices[5];
printf("%d\n", p4 - p3); // 20

  Pointer minus pointer , The result is how many points are separated between these two pointers “ Corresponding to the type ” The data of .

Comparison of pointers

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
for (int *p1 = prices; p1 < prices + 8; p1++) {
	printf("%d ", *p1);  //  Forward output various prices 
}

printf("\n");

for (int* p1 = prices+7; p1 >= prices; p1--) {
	printf("%d ", *p1);  //  Reverse output various prices 
}

Comparison of pointers , Is stored in the pointer “ Address values ”, Compare according to the rules of unsigned integers .