One 、 Pre reminder

  sizeof() It's a monocular operator , Used to calculate the length of data , In bytes
  strlen yes C A function defined by the language standard library , Used to calculate the length of a string , Until the empty end character , But does not include the null end character . Looking at the source code, we can see ,strlen To receive a pointer , That is to receive an address .
   The array name is the address of the first element of the array , But there are 2 Exceptions ：1.sizeof( Array name ), Here, the array name represents the whole array ;2. & Array name , Here, the array name represents the whole array , It takes out the address of the entire array .

Two 、 One dimensional array

   First calculate the print result , Then look at the answers behind , written examination ！！！ Do not copy directly to the compiler .

1. Shape array

int main() {
    
	int a[] = {
     1,2,3,4 };
	printf("%d\n", sizeof(a));
	printf("%d\n", sizeof(a + 0));
	printf("%d\n", sizeof(*a));
	printf("%d\n", sizeof(a + 1));
	printf("%d\n", sizeof(a[1]));

	printf("%d\n", sizeof(&a));
	printf("%d\n", sizeof(*&a));
	printf("%d\n", sizeof(&a + 1));
	printf("%d\n", sizeof(&a[0]));
	printf("%d\n", sizeof(&a[0] + 1));

	return 0;
}

int main() {
    
	// Here are 32 Calculation results in the case of bit machine 
	int a[] = {
     1,2,3,4 };
	printf("%d\n", sizeof(a));
	// One int Type account 4 Bytes ,4 individual int type , The result is 16
	printf("%d\n", sizeof(a + 0));
	//a As an array name, it does not appear alone , So here a Represents the address of the first element 
	// First element address +0 after , Or the first element address 
	// The size of an address is 4
	printf("%d\n", sizeof(*a));
	//a Represents the address of the first element ,*a Is to dereference the address of the first element , Get integer 1
	// An integer size is 4 Bytes 
	printf("%d\n", sizeof(a + 1));
	//a + 1 What you get is the address of the second element 
	// The size of an address is 4
	printf("%d\n", sizeof(a[1]));
	//a[1] What you get is the second element 
	//int The type size is 4 Bytes 
	
	printf("%d\n", sizeof(&a));
	// Get the address of the entire array , The address of the array is also the address 
	// The size of an address is 4
	printf("%d\n", sizeof(*&a));
	//&a What you get is the address of the whole element , Dereference and get the whole array 
	//4 individual int type , The result is 16
	printf("%d\n", sizeof(&a + 1));
	//&a Get an address , Address +1 After that, I got an address 
	// The size of an address is 4
	printf("%d\n", sizeof(&a[0]));
	// The operator [] The priority ratio & high 
	// First a[0], Represents the first element of the array 
	// Then take the address &, Get the address of the first element 
	printf("%d\n", sizeof(&a[0] + 1));
	// At the address of the first element +1, Get the address of the second element 

	return 0;
}

2. A character array

int main() {
    
	char arr[] = {
     'a','b','c','d','e','f' };
	printf("%d\n", sizeof(arr));
	printf("%d\n", sizeof(arr + 0));
	printf("%d\n", sizeof(*arr));
	printf("%d\n", sizeof(arr[1]));
	printf("%d\n", sizeof(&arr));
	printf("%d\n", sizeof(&arr + 1));
	printf("%d\n", sizeof(&arr[0] + 1));

	printf("%d\n", strlen(arr));
	printf("%d\n", strlen(arr + 0));
	printf("%d\n", strlen(*arr));
	printf("%d\n", strlen(arr[1]));
	printf("%d\n", strlen(&arr));
	printf("%d\n", strlen(&arr + 1));
	printf("%d\n", strlen(&arr[0] + 1));

	return 0;
}

int main() {
    
	// Here are 32 Calculation results in the case of bit machine 
	char arr[] = {
     'a','b','c','d','e','f' };
	printf("%d\n", sizeof(arr));
	// One char The type size is 1 byte ,6 individual char type , Print 6
	printf("%d\n", sizeof(arr + 0));
	//arr As an array name, it does not appear alone , So here arr Represents the address of the first element 
	// First element address +0 after , Or the first element address 
	// The size of an address is 4 byte 
	printf("%d\n", sizeof(*arr));
	//arr Represents the address of the first element , Get the first element after dereferencing 
	// One char The type size is 1 byte 
	printf("%d\n", sizeof(arr[1]));
	// For the second element , One char The type size is 1 byte 
	printf("%d\n", sizeof(&arr));
	// Get the address of the entire array , The size of an address is 4 byte 
	printf("%d\n", sizeof(&arr + 1));
	// Get the address of the entire array , Then the address +1, Get another address 
	printf("%d\n", sizeof(&arr[0] + 1));
	// Get the address of the first element +1, Get the address of the second element 

	// Be careful ： Here is strlen, No sizeof 了 , Do not continue to use sizeof count （doge）
	printf("%d\n", strlen(arr));
	//strlen find ‘\0’ Just stop ,
	// however arr There's no storage ‘\0’
	// that strlen I'll keep looking for it , Until you find one ‘\0’ until 
	// So it prints out as a random value 
	printf("%d\n", strlen(arr + 0));
	//arr+0 Get the first element ,
	// Then calculate from the first element , It turns out that there is still no ‘\0’
	// So the compiler silently prints a random value 
	printf("%d\n", strlen(*arr));
	//*arr Dereference to get characters ‘a’,
	// The problem arises ,strlen Only receive addresses 
	// So this line of code is wrong 
	printf("%d\n", strlen(arr[1]));
	//arr[1] Get the characters ‘b’, Report errors 
	printf("%d\n", strlen(&arr));
	//&arr Get the address of the entire array ,
	//BUT This array has no ‘\0’,
	// So the compiler silently prints a random value 
	printf("%d\n", strlen(&arr + 1));
	//&arr + 1 Get an address 
	//BUT The devil knows ‘\0’ Where will it appear 
	// So the compiler silently prints a random value 
	printf("%d\n", strlen(&arr[0] + 1));
	// After getting the address of the first element +1, Get the second element 
	//BUT The second element is unknown ‘\0’ Where will it appear 
	// So the compiler silently prints a random value 

	return 0;
}

int main() {
    
	char arr[] = "abcdef";
	printf("%d\n", sizeof(arr));
	printf("%d\n", sizeof(arr + 0));
	printf("%d\n", sizeof(*arr));
	printf("%d\n", sizeof(arr[1]));
	printf("%d\n", sizeof(&arr));
	printf("%d\n", sizeof(&arr + 1));
	printf("%d\n", sizeof(&arr[0] + 1));

	printf("%d\n", strlen(arr));
	printf("%d\n", strlen(arr + 0));
	printf("%d\n", strlen(*arr));
	printf("%d\n", strlen(arr[1]));
	printf("%d\n", strlen(&arr));
	printf("%d\n", strlen(&arr + 1));
	printf("%d\n", strlen(&arr[0] + 1));

	return 0;
}

int main() {
    
	// Here are 32 Calculation results in the case of bit machine 
	char arr[] = "abcdef";
	printf("%d\n", sizeof(arr));
	// Strings are stored with ‘\0’
	//sizeof No strlen, It will also have a ‘\0’
	// therefore 7 individual char type , Print 7
	printf("%d\n", sizeof(arr + 0));
	//arr As an array name, it does not appear alone , So here arr Represents the address of the first element 
	// First element address +0 after , Or the first element address 
	// The size of an address is 4 byte 
	printf("%d\n", sizeof(*arr));
	// here arr Represents the address of the first element , The first element after dereference , One char The type size is 1
	printf("%d\n", sizeof(arr[1]));// For the second element , One char The type size is 1
	printf("%d\n", sizeof(&arr));// The address of the entire array , The size of an address is 4
	printf("%d\n", sizeof(&arr + 1));// Address +1 Get the address , The size of an address is 4
	printf("%d\n", sizeof(&arr[0] + 1));// Get the address of the second element , The size of an address is 4

	printf("%d\n", strlen(arr));
	// Strings are stored with ‘\0’
	//strlen encounter ‘\0’ Just stop , And do not calculate ‘\0’
	// So print 6
	printf("%d\n", strlen(arr + 0));
	// Get the address of the first character , Start calculating the length , encounter ‘\0’ Just stop , Print 6
	printf("%d\n", strlen(*arr));//strlen To receive address , Report errors 
	printf("%d\n", strlen(arr[1]));//strlen To receive address , Report errors 
	printf("%d\n", strlen(&arr));// Take the address of the whole array , Print 6
	printf("%d\n", strlen(&arr + 1));
	// Take the address of the whole array ,+1 Skip this array 
	// So I don't know where there is ‘\0’ 了 
	// Print a random value 
	printf("%d\n", strlen(&arr[0] + 1));// Fetch ‘b’ The address of , Start calculating , The result is 5

	return 0;
}

3、 ... and 、 Two dimensional array

int main() {
    
	// Two dimensional array 
	int a[3][4] = {
     0 };
	printf("%d\n", sizeof(a));
	printf("%d\n", sizeof(a[0][0]));
	printf("%d\n", sizeof(a[0]));
	printf("%d\n", sizeof(a[0] + 1));
	printf("%d\n", sizeof(*(a[0] + 1)));
	printf("%d\n", sizeof(a + 1));
	printf("%d\n", sizeof(*(a + 1)));
	printf("%d\n", sizeof(&a[0] + 1));
	printf("%d\n", sizeof(*(&a[0] + 1)));
	printf("%d\n", sizeof(*a));
	printf("%d\n", sizeof(a[3]));

	return 0;
}

int main() {
    
	// Two dimensional array 
	int a[3][4] = {
     0 };
	printf("%d\n", sizeof(a));
	// Two dimensional array with three rows and four columns , All are int type 
	//3 * 4 * 4 have to 48
	printf("%d\n", sizeof(a[0][0]));// The first element in the first line , Print 4
	printf("%d\n", sizeof(a[0]));
	//a[0] As an array, the list is placed alone in sizeof Inside , The first line 
	// One line is stored 4 individual int Type element , have to 16
	printf("%d\n", sizeof(a[0] + 1));
	//a[0] Not alone in sizeof Inside , No address , Represents the address of the first element in the first line ,
	//+1 Get the address of the second element in the first line , The size of an address is 4
	printf("%d\n", sizeof(*(a[0] + 1)));// Dereference to get the second element in the first line , One int The type size is 4
	printf("%d\n", sizeof(a + 1));
	// Represents the address of the first element , That's the first row 
	//+1 Get the second line of address , The size of an address is 4
	printf("%d\n", sizeof(*(a + 1)));// Dereference to get the second row array ,4 individual int The type size is 16
	printf("%d\n", sizeof(&a[0] + 1));//&a[0] Get the first line address ,&a[0] + 1 Get the second line of address ,4
	printf("%d\n", sizeof(*(&a[0] + 1)));// Dereference the second line , Get the second row array ,4 individual int The type size is 16
	printf("%d\n", sizeof(*a));//a Represents the address of the first element , The first row array of dereference ,4 individual int The type size is 16
	printf("%d\n", sizeof(a[3]));
	// If it exists ,a[3] Represents the array name of the fourth row ,
	//sizeof It doesn't need to exist , Calculate the type ,4 individual int The type size is 16

	return 0;
}

Four 、 The pointer

int main() {
    
	char* p = "abcdef";
	printf("%d\n", sizeof(p));
	printf("%d\n", sizeof(p + 1));
	printf("%d\n", sizeof(*p));
	printf("%d\n", sizeof(p[0]));
	printf("%d\n", sizeof(&p));
	printf("%d\n", sizeof(&p + 1));
	printf("%d\n", sizeof(&p[0] + 1));

	printf("%d\n", strlen(p));
	printf("%d\n", strlen(p + 1));
	printf("%d\n", strlen(*p));
	printf("%d\n", strlen(p[0]));
	printf("%d\n", strlen(&p));
	printf("%d\n", strlen(&p + 1));
	printf("%d\n", strlen(&p[0] + 1));

	return 0;
}

int main() {
    
	char* p = "abcdef";
	printf("%d\n", sizeof(p));//p It's a pointer , The address , The size of an address is 4
	printf("%d\n", sizeof(p + 1));// Address +1 It's still an address , The size is 4
	printf("%d\n", sizeof(*p));
	// The pointer P It stores the first element ‘a’ The address of 
	// Dereference to get the element ‘a’
	// One char The size of the type is 1
	printf("%d\n", sizeof(p[0]));//p[0] Quite so p To dereference , Get the element ‘a’, The size is 1
	printf("%d\n", sizeof(&p));
	// Pointer is also a variable , He will also open up an address to store 
	// take p The address of is still an address , The size is 4
	printf("%d\n", sizeof(&p + 1));// Address +1 It's still an address , The size is 4
	printf("%d\n", sizeof(&p[0] + 1));
	// obtain ‘a’ After the address of 
	// Right again ‘a’ Take the address to get an address 
	// The size of an address is 4

	printf("%d\n", strlen(p));//p Deposit is ‘a’ The address of , from ‘a’ Start calculating , The result is 6
	printf("%d\n", strlen(p + 1));//p+1 Get back ‘b’ The address of , from ‘b’ Start calculating , The result is 5
	printf("%d\n", strlen(*p));//p After dereferencing, we get ‘a’,strlen To receive an address , Report errors 
	printf("%d\n", strlen(p[0]));//p[0] Quite so p To dereference , Get the element ‘a’, Report errors 
	printf("%d\n", strlen(&p));
	// Get pointer p The address of , from p Start to calculate the address of 
	// But I don't know where there will be ‘\0’, So print out a random value 
	printf("%d\n", strlen(&p + 1));// Random value 
	printf("%d\n", strlen(&p[0] + 1));
	//p[0] Quite so p To dereference , Get the element ‘a’
	// Right again ‘a’ Address fetch , obtain ‘a’ The address of ,+1 obtain ‘b’ The address of 
	// from ‘b’ Start calculating , The result is 5

	return 0;
}

   Is this ？ Is this ？ Is this ？ Isn't it about two handfuls of hair ？