C Language----pointers

I. Declaration

int  *p ;   //   int  * ）( p )

Second, wild pointer--avoidance method

1) The pointer variable must be initialized to NULL, because any pointer variable that was just created will not automatically become a null pointer, and its default value is random.
2) When the memory space that the pointer p points to is released, the value of the pointer p is not set to null. Delete and free simply freed up the memory space, but did not assign the value of the pointer p to null. It is common to judge whether a pointer is legitimate, and whether the pointer is null by using the IF statement. For example:

int*p=newint(6);delete p;if(p!=NULL){*p=7;cout<<p<<endl;}

The correct wording should be the following code:

int*p=newint(6);delete p;p=NULL;if(p!=NULL){*p=7;cout<<p<<endl;}

So after allocating memory dynamically, if you use the dynamically allocated memory space, you must habitually use the delete operator to release it.

Third, struct pointer access member variable:

（*p）.sex = ‘m’  p->sex = ‘m‘

(*p) is a struct variable after the pointer is evaluated. Sex is an access member variable use pointers to directly access the struct body
Member variable P--sex.

IV. structure arrays and pointers

The array name of the struct array is the struct pointer constant.

The array is characterized by: the array name is the first address of an array element;
The array name of the struct array is the first address of the element of the initial struct type;
A struct pointer is manipulated to manipulate an array of structures.

Five

Pointer to an array of n elements.

int  array[2][3* ( * ( p + 1 )  + 1 )  

int p[3] p is an array that has 3 elements, each of which is of type int, which is a pointer type that points to the integer data.

int a=10,b=20,c=30;int*p[3]={&a,&b,&c};

The p in int (*p) [3] is a pointer to an array that has 3 elements of type int. For example:

a[3]={1,2,3}; 那么p就是指向这个数组a的指针。int(*p)[3]=&a; // 这里赋值一定要用取地址符号。也就是取数组a的地址。

You cannot assign this value: Int (p) [3]=a;//Error: Type is incompatible. A is an array type and is not assignable to an int () [3] of this type.

But this is possible int p1=a;//OK because a can be implicitly converted to an int type whose value is actually the address of the first element of the array, which is &a[0]

*P[3] This is a pointer array which means that each element is equivalent to a pointer variable
and (*p) [3] p is a pointer variable representing a one-dimensional array that contains 3 integral elements

The former can be similar to a two-dimensional array to consider it to be composed of 3 one-dimensional arrays are often used in conjunction with strings to use a more convenient operation to put multiple strings in a pointer array
The latter is used to refer to a two-dimensional array of like a[2][3] This two-dimensional array we can use both pointers to reference and can be used (*P) [3] to refer to general usage (*P) [3]

Cases:

intMain () {intI,j;inta[2][3]={3,4,5,6,7,8};int*p[3] ;//Indicates that the storage is 3 integer variable address;int(*Q) [3];//Represents a one-dimensional array pointer to a 3 integer array element//Put the address of the first three elements in the P-pointer array. for(i=0;i<3; ++i) p[i]=&a[0][i];//The corresponding value of the address in the output pointer array for(j=0;j<3; ++j)cout<< *p[j]<<" ";cout<<endl;q=a;//Assign the array a start address to a one-dimensional array q; for(i=0;i<2; i++) for(j=0;j<3; j + +)cout<< * (* (q+i) +j) <<" ";//output array of elementsreturn 0;}

• This article reference from Baidu Encyclopedia

C Language----pointers