C++ Tutorial/Development/new
Содержание
- 1 Allocate an array
- 2 Allocate an array of objects by overloading new and delete operators
- 3 Allocate an object
- 4 Allocate memory for an object
- 5 Catch "new" memory allocation exception
- 6 dynamically allocated objects may have constructors and destructors
- 7 Global new
- 8 Initialize memory
- 9 Use new and delete
- 10 using new to get memory for strings
Allocate an array
<source lang="cpp">#include <iostream>
- include <new>
using namespace std;
int main() {
int *p, i;
try {
p = new int [10]; // allocate 10 integer array
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
for(i=0; i<10; i++ )
p[i] = i;
for(i=0; i<10; i++)
cout << p[i] << " ";
delete [] p; // release the array
return 0;
}</source>
0 1 2 3 4 5 6 7 8 9
Allocate an array of objects by overloading new and delete operators
<source lang="cpp">#include <iostream>
- include <cstdlib>
- include <new>
using namespace std; class Point {
int x, y;
public:
Point() {x = y = 0;}
Point(int px, int py) {
x = px;
y = py;
}
void show() {
cout << x << " ";
cout << y << "\n";
}
void *operator new(size_t size);
void operator delete(void *p);
void *operator new[](size_t size);
void operator delete[](void *p);
}; // new overloaded relative to Point. void *Point::operator new(size_t size) { void *p;
cout << "In overloaded new.\n";
p = malloc(size);
if(!p) {
bad_alloc ba;
throw ba;
}
return p;
} // delete overloaded relative to Point. void Point::operator delete(void *p) {
cout << "In overloaded delete.\n"; free(p);
} // new overloaded for Point arrays. void *Point::operator new[](size_t size) {
void *p;
cout << "Using overload new[].\n";
p = malloc(size);
if(!p) {
bad_alloc ba;
throw ba;
}
return p;
} // delete overloaded for Point arrays. void Point::operator delete[](void *p) {
cout << "Freeing array using overloaded delete[]\n"; free(p);
} int main() {
Point *p1, *p2;
int i;
try {
p1 = new Point (10, 20); // allocate an object
} catch (bad_alloc xa) {
cout << "Allocation error for p1.\n";
return 1;;
}
try {
p2 = new Point [10]; // allocate an array
} catch (bad_alloc xa) {
cout << "Allocation error for p2.\n";
return 1;;
}
p1->show();
for(i=0; i<10; i++)
p2[i].show();
delete p1; // free an object
delete [] p2; // free an array
return 0;
}</source>
In overloaded new. Using overload new[]. 10 20 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 In overloaded delete. Freeing array using overloaded delete[]
Allocate an object
<source lang="cpp">#include <iostream>
- include <new>
using namespace std;
class Rectangle {
int width; int height;
public:
Rectangle(int w, int h) {
width = w;
height = h;
cout << "Constructing " << width << " by " << height << " rectangle.\n";
}
~Rectangle() {
cout << "Destructing " << width << " by " << height << " rectangle.\n";
}
int area() {
return width * height;
}
};
int main() {
Rectangle *p;
try {
p = new Rectangle(10, 8);
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
cout << "Area is " << p->area();
delete p;
return 0;
}</source>
Constructing 10 by 8 rectangle. Area is 80Destructing 10 by 8 rectangle.
Allocate memory for an object
<source lang="cpp">#include <iostream>
- include <new>
using namespace std;
class Rectangle {
int width; int height;
public:
Rectangle(int w, int h) {
width = w;
height = h;
cout << "Constructing " << width << " by " << height << " rectangle.\n";
}
~Rectangle() {
cout << "Destructing " << width << " by " << height << " rectangle.\n";
}
int area() {
return width * height;
}
};
int main() {
Rectangle *p;
try {
p = new Rectangle(10, 8);
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
cout << "Area is " << p->area();
delete p;
return 0;
}</source>
Constructing 10 by 8 rectangle. Area is 80Destructing 10 by 8 rectangle.
Catch "new" memory allocation exception
<source lang="cpp">#include <iostream>
- include <new>
using namespace std;
class Rectangle {
int width; int height;
public:
Rectangle(int w, int h) {
width = w;
height = h;
cout << "Constructing " << width << " by " << height << " rectangle.\n";
}
~Rectangle() {
cout << "Destructing " << width << " by " << height << " rectangle.\n";
}
int area() {
return width * height;
}
};
int main() {
Rectangle *p;
try {
p = new Rectangle(10, 8);
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
cout << "Area is " << p->area();
delete p;
return 0;
}</source>
Constructing 10 by 8 rectangle. Area is 80Destructing 10 by 8 rectangle.
dynamically allocated objects may have constructors and destructors
<source lang="cpp">#include <iostream>
- include <new>
- include <cstring>
using namespace std;
class balance {
double cur_bal; char name[80];
public:
balance(double n, char *s) {
cur_bal = n;
strcpy(name, s);
}
~balance() {
cout << "Destructing ";
cout << name << "\n";
}
void get_bal(double &n, char *s) {
n = cur_bal;
strcpy(s, name);
}
};
int main() {
balance *p;
char s[80];
double n;
// this version uses an initializer
try {
p = new balance (1.1, "A");
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
p->get_bal(n, s);
cout << s << ""s balance is: " << n;
cout << "\n";
delete p;
return 0;
}</source>
Global new
<source lang="cpp">#include <iostream>
- include <cstdlib>
- include <new>
using namespace std; class Point {
int x, y;
public:
Point() {}
Point(int px, int py) {
x = px;
y = py;
}
void show() {
cout << x << " ";
cout << y << "\n";
}
}; // Global new void *operator new(size_t size) {
void *p;
p = malloc(size);
if(!p) {
bad_alloc ba;
throw ba;
}
return p;
} // Global delete void operator delete(void *p) {
free(p);
} int main() {
Point *p1, *p2;
float *f;
try {
p1 = new Point (10, 20);
} catch (bad_alloc xa) {
cout << "Allocation error for p1.\n";
return 1;;
}
try {
p2 = new Point (-10, -20);
} catch (bad_alloc xa) {
cout << "Allocation error for p2.\n";
return 1;;
}
try {
f = new float; // uses overloaded new, too
} catch (bad_alloc xa) {
cout << "Allocation error for f.\n";
return 1;;
}
*f = 10.10F;
cout << *f << "\n";
p1->show();
p2->show();
delete p1;
delete p2;
delete f;
return 0;
}</source>
10.1 10 20 -10 -20
Initialize memory
<source lang="cpp">#include <iostream>
- include <new>
using namespace std;
int main() {
int *p;
try {
p = new int (87); // initialize to 87
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
cout << "At " << p << " is the value " << *p << "\n";
delete p;
return 0;
}</source>
At 0x3d2448 is the value 87
Use new and delete
<source lang="cpp">#include <iostream>
- include <new>
using namespace std;
int main() {
int *p;
try {
p = new int; // allocate space for an int
} catch (bad_alloc xa) {
cout << "Allocation Failure\n";
return 1;
}
*p = 100;
cout << "At " << p << " is the value " << *p << "\n";
delete p;
return 0;
}</source>
At 0x3d2448 is the value 100
using new to get memory for strings
<source lang="cpp">#include <iostream>
#include <cstring>
using namespace std;
class String {
private:
char* str;
public:
String(char* s){
int length = strlen(s);
str = new char[length+1];
strcpy(str, s);
}
~String() {
delete[] str;
}
void display(){
cout << str << endl;
}
};
int main()
{
String s1 = "this is a test";
cout << "s1=";
s1.display();
return 0;
}</source>
