In C ++, the usage of New is very flexible in C ++. Here is a simple summary: "') X5 T # D/S # V) v9 n w! J
1. New () allocates a memory space of this type and initializes this variable with the value in parentheses;. u * t, V #~ % U
2. New [] allocates n Memory Spaces of this type and uses the default constructor to initialize these variables. 8 A6 r I) '6g % m L
# Include <iostream>
. | 1 U "Q6 Z (y '? /V3 R A1 ~ # Include <cstring>
) W $ t/m, X8 N6 V9 qusing namespace STD;) @ 8 B 'J-I, F W $ q $ Z
Int main () {7 o8 Z "H1/4 J8 A8 R
// Char * P = new char ("hello"); 6 @ 0 @ 4 A8 C %/6 r
// Error allocates a char (1 byte) space,
$ S K1 S (K9 H. Y; M & // use "hello" for initialization, which is obviously incorrect
7 C7 B3 q )~ (M. F (? 6 {char * P = new char [6];
-C8 p $ A 'l1 x0 K0 E // P = "hello ";
% ^; ^ & B7 F! K3 B! {9 y // The character string cannot be directly assigned to the pointer P because: 'c3 {6 _) L7 P % Q2 U "s
// The pointer P points to the first character of the string and can only use the following * I3 M * Z2 D; A +/"L7 M # T
// Strcpy
/M, F4 o % x9 ') s! Ystrcpy (P, "hello ");
! L1 H7 J1 t F3 U ([! Ecout <* P <Endl; // only outputs the first character of the string pointed to by P!
3 B6} q0 a %/4 Z "'" s * bcout <p <Endl; // output the string pointed to by P!
* B3 R 'B' _; D, idelete [] P;-Q % K E W; y
Return 0;} 7 U) M4 | * B8 e 'P: V
Output result:
6 B-X2 U/N $ U0 X-L6 ^ h
# K * t 'n5 E & C: lhello; P0 X % Z! [5 V8 J; l! ~; ^ & D //
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:
6 m3 I * I4 a %} 0 F! I1 U/J int * P1 = new int [10];
0 G5 X-D % F5 ^ * M returns an int pointer int * + L $ U; A + [0 u8 K
INT (* P2) [10] = new int [2] [10];
, {2 T: M $ R! P; ': M6 y (hnew has a two-dimensional array, removing the leftmost one [2] and leaving int [10], therefore, a pointer int (*) [10] pointing to a one-dimensional array such as int [10] is returned.
) F {'j1 ~ 4 E6 S/J, N % [int (* P3) [2] [10] = new int [5] [2] [10]; A new three-dimensional array, remove the leftmost one [5] and INT [2] [10]. Therefore, a pointer int (*) pointing to the two-dimensional array int [2] [10] is returned (*) [2] [10].
6 M0 x +/%] 6 y * F & I # include <iostream>
6 K0 | 9 t @ 5 C $ L3 D8 '# include <typeinfo>
& V) M: ^ 6 J: Y5] (x 'uusing namespace STD;-@. q B $ F: [(h
Int main (){
# @ % A + K2 K; U; L * @/qint * A = new int [34];
(U * O7 Z! Q7 lint * B = new int [];
-U % a3 ~ 2 F + W: I & xint (* C) [2] = new; M/L1] 3 L) I] "g1 s" x/S & H
Int [34] [2];
; F, J "? F2 M8 V -~ 6 xint (* D) [2] = new int [] [2];
4G; s: R6 T-^ $ V: hint (* E) [2] [3] = new int [34] [2] [3];) S, _ 6 B & F4 J/C-z/y/L-u, G "P
INT (* f) [2] [3] = new int [] [2] [3];
7? 4 i8 U. K6 S (D-|, _: D5 k m $ H a [0] = 1; + P6 N0 a "v" W: J3 E
B [0] = 1; // runtime error, no memory allocation, B only acts as a pointer, used to point to the corresponding data/P9 N _ + _-R ./
C [0] [0] = 1;
) T-y $ U1 @ 9 o "U0 E: X) T. rd [0] [0] = 1; // runtime error, no allocated memory, d only acts as a pointer, used to point to the corresponding data-I0 ^: D (C; n-! V "J
E [0] [0] [0] = 1;
/T-J5 I (k # Y. t5 X6 [f [0] [0] [0] = 1; // runtime error, no allocated memory, F only acts as a pointer, used to point to the corresponding data
, |: O (} 2/$ x * F6 | % J. fcout <typeid (a). Name () <Endl ;! U. D "d # Q (I % R
Cout <typeid (B). Name () <Endl;: B8 l % Z-W4 V6 e $ Y3 y! [& D
Cout <typeid (c). Name () <Endl;
8 [5 A2 I + B $ P/X! ~ : B/bcout <typeid (d). Name () <Endl;. _ 9 H9 K3 g /?
Cout <typeid (e). Name () <Endl;
+ J + '& Q5 V (K cout <typeid (f ). name () <Endl ;. j9 '% R * s) L * A8 U "}; D *~
Delete [] A; Delete [] B; Delete [] C;
2 L7 B "/9 ^; U1 W 'C) Q7 |:] Delete [] D; Delete [] E; Delete [] F; 5] 5 H0 s "F3 G-r-D. b8 R/J
} & Y6 R1 l0 J & I % R6 F & C1
Output result:
0} 9 R0 I % S $} int * (} "Q #]" U % v) P! /8 _ "y! ]
Int *
3 Z4 T1 D * K % H4 D (S % A. P % N % RINT (*) [2]
3 Q (o) Z! K'w3 T5 X8 o'] int (*) [2]
1 R2? $ D9 ~; J # R5 k'x: T, Bint (*) [2] [3] $ V/U (A: P &[
INT (*) [2] [3]
