C ++ pointer 1: pointer

C ++ pointer 1: pointer

The pointer is also a variable that occupies the memory space and is used to save the memory address.

A pointer is also a data type, which refers to the Data Type of memory space caused by it.

Pointer variables and memory blocks it points to are two different concepts

* P operation memory

When the pointer is declared, * indicates that the declared variable is a pointer.

* Indicates the value in the memory space pointed to by the Operation pointer.

* P is equivalent to finding a piece of memory through the address (value of the p variable;

Then the operation memory * p is placed on the left of the equal sign and assigned a value to the memory)

* Put p to the right of the equal sign (get value from memory)

# Include <iostream> using namespace std; # include <stdio. h> void change (int num) {num = 666;} void changeA (int * num) {* num = 666;} void printfSingleArrayInt (int * p, int n) {cout <"/********************************** /"<endl; cout <p <endl; cout <sizeof (p) <endl; // 4 for (int I = 0; I <n; I ++) {cout <* (p + I) <endl ;} cout <"/**********************************/ "<endl ;} void printfSingleArrayIntS (int a [10]) {cout <"/ * **************** S ********************/"<endl; cout <sizeof (a) <endl; // 4 for (int I = 0; I <10; I ++) {cout <* (a + I) <endl ;} cout <"/**********************************/ "<endl ;} int main () {int a [10] = {0}; for (int I = 0; I <10; I ++) {a [I] = I ;} int * p; // the pointer step, which is determined based on the memory space type. Cout <sizeof (p) <endl; // 4 p = a; cout <sizeof (p) <endl; // 4 cout <sizeof () <endl; // 40 cout <sizeof (a + 1) <endl; // 4 cout <sizeof (& a) <endl; // 4 cout <sizeof (& a + 1) <endl; // 4 printfSingleArrayInt (p, 10); printfSingleArrayIntS (); printf ("% d \ n", a, a + 1); printf ("% d \ n", & a, & a + 1 ); return 0;} int main01 () {int num = 100; int * p = & num; cout <& num <endl; // print the num address num = 1; // directly modify the value of num cout <num <endl; // print the value of num * p = 100000; // indirectly modify the num value // * put p on the left of the equal sign to indirectly modify the memory space value/*** p meaning: * is like a key, modify the memory space of the backdoor based on the value of a pointer variable **/cout <num <endl; change (num); cout <num <endl; /* three conditions for indirect value assignment a) two variables (usually one real parameter, one form parameter) B) establish a relationship, and the real parameter access address is assigned to the form parameter pointer c) * The p-type parameter indirectly modifies the value of the real parameter */changeA (p); cout <num <endl; int a = * p; /// * put p on the right of the equal sign and take the cout value from the memory space <a <endl;/* {char * B = NULL; * B = 'J';} */return 0 ;}

Cout <sizeof (a) <endl; // The length of the Data Type contained in the address 40
Cout <sizeof (a + 1) <endl; // 4
Cout <sizeof (& a) <endl; // 4 & a is the address of array a, which occupies four bytes
Cout <sizeof (& a + 1) <endl; // 4 & a + 1 is the address of array a + 1, which occupies four bytes

The printed addresses of the three elements a, a [0], and & a are the same.

A + I indicates that memory address a is used to move the I int address.

    printf("%d %d\n",a,a+1);

    printf("%d %d\n",&a,&a+1);

What are the differences between & a and & a + 1?

& A indicates that the array is regarded as a whole address.

& A + 1 indicates that the array moves an element (array) as a whole ).

Three conditions for indirect assignment

A) two variables (usually one real parameter, one form parameter) B) establish a relationship, and the real parameter access address is assigned to the shape parameter c) * p form parameter indirectly modifies the value of the real Parameter