C ++ new usage

In C ++, the usage of New is flexible. Here is a simple summary:

1. New () allocates a memory space of this type and initializes this variable with the value in parentheses;

2. New [] allocates n Memory Spaces of this type and uses the default constructor to initialize these variables;

# Include <iostream>

# Include <cstring>

Using namespace STD;

Int main (){

// Char * P = new char ("hello ");

// Error allocates a char (1 byte) space,

// Use "hello" for initialization. This is obviously incorrect.

Char * P = new char [6];

// P = "hello ";

// The string cannot be directly assigned to the pointer P, because:

// The pointer P points to the first character of the string.

// Strcpy

Strcpy (P, "hello ");

Cout <* P <Endl; // only outputs the first character of the string pointed to by P!

Cout <p <Endl; // output the string pointed to by P!

Delete [] P;

Return 0 ;}

Output result:

H

Hello

3. When the new operator is used to define a multi-dimensional array variable or array object, it generates a pointer to the first element of the array. The returned type retains all dimensions except the leftmost dimension. For example:

Int * P1 = new int [10];

Returns an int x pointer to an int *

INT (* P2) [10] = new int [2] [10];

A two-dimensional array is added, and the leftmost one [2] is removed, with int [10] Left. Therefore, a pointer int (*) pointing to a one-dimensional array such as int [10] is returned (*) [10].

INT (* P3) [2] [10] = new int [5] [2] [10]; new a three-dimensional array, remove the leftmost one [5], there is also int [2] [10], so a pointer to the two-dimensional array int [2] [10] type int (*) [2] [10] is returned.

# Include <iostream>

# Include <typeinfo>

Using namespace STD;

Int main (){

Int * A = new int [34];

Int * B = new int [];

INT (* C) [2] = new

Int [34] [2];

INT (* D) [2] = new int [] [2];

INT (* E) [2] [3] = new int [34] [2] [3];

INT (* f) [2] [3] = new int [] [2] [3];

A [0] = 1;

B [0] = 1; // runtime error, no memory allocated, B only acts as a pointer, used to point to the corresponding data

C [0] [0] = 1;

D [0] [0] = 1; // runtime error, no allocated memory, d only acts as a pointer, used to point to the corresponding data

E [0] [0] [0] = 1;

F [0] [0] [0] = 1; // runtime error, no memory allocated. F only acts as a pointer and is used to point to the corresponding data

Cout <typeid (a). Name () <Endl;

Cout <typeid (B). Name () <Endl;

Cout <typeid (c). Name () <Endl;

Cout <typeid (d). Name () <Endl;

Cout <typeid (e). Name () <Endl;

Cout <typeid (f). Name () <Endl;

Delete [] A; Delete [] B; Delete [] C;

Delete [] D; Delete [] E; Delete [] F;

}

Output result:

Int *

Int *

INT (*) [2]

INT (*) [2]

INT (*) [2] [3]

INT (*) [2] [3]