C++/Pointer/Pointer Primitive — различия между версиями
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Версия 14:21, 25 мая 2010
Содержание
- 1 Assign the public object member address to a pointer
- 2 Declares a pointer and then outputs its value without first assigning
- 3 Decrementing a Pointer for int value
- 4 How to use the address operator to assign the address of a variable to a pointer
- 5 Indirection Operator and Dereferencing
- 6 Null Pointers
- 7 Pointer as a Variable
- 8 Pointers to Class Members
- 9 Prints the values and addresses of variables.
- 10 Returning a pointer
- 11 The actual data type of the value of all pointers is the same
- 12 Using a reference parameter for class type
Assign the public object member address to a pointer
#include <iostream>
using namespace std;
class MyClass {
public:
int i;
MyClass(int j) {
i = j;
}
};
int main()
{
MyClass myObject(1);
int *p;
p = &myObject.i;
cout << *p;
return 0;
}
Declares a pointer and then outputs its value without first assigning
#include <iostream>
using namespace std;
int main ()
{
int* intPointer;
cout << "The value of intPointer is " << intPointer << endl;
return 0;
}
Decrementing a Pointer for int value
#include <iostream>
using namespace std;
const int Length = 3;
int main ()
{
int testScore[Length] = {4, 7, 1};
int* intPointer = &testScore[Length - 1];
int i = Length - 1;
while (intPointer >= &testScore[0])
{
cout << "The address of index " << i
<< " of the array is "<< intPointer << endl;
cout << "The value at index " << i
<< " of the array is "<< *intPointer << endl;
intPointer--;
i--;
}
return 0;
}
How to use the address operator to assign the address of a variable to a pointer
#include <iostream>
using namespace std;
int main ()
{
int num = 5;
int* intPointer = #
cout << "The address of x using &num is " << &num << endl;
cout << "The address of x using intPointer is " << intPointer << endl;
return 0;
}
Indirection Operator and Dereferencing
#include <iostream>
using namespace std;
int main ()
{
int num = 5;
int* intPointer = #
cout << "The value of num is " << num << endl;
num = 10;
cout << "The value of num after num = 10 is " << num << endl;
*intPointer = 15;
cout << "The value of num after *intPointer = 15 is " << num << endl;
return 0;
}
Null Pointers
#include <iostream>
using namespace std;
int main ()
{
int* intPointer;
intPointer = NULL;
cout << "The value of intPointer is " << intPointer << endl;
return 0;
}
Pointer as a Variable
#include <iostream>
using namespace std;
int main ()
{
int num1 = 5, num2 = 14;
int* intPointer = &num1;
cout << "The value of num1 is " << num1 << endl;
*intPointer *= 2;
cout << "The value of num1 after *intPointer *= 2 is " << *intPointer << endl;
intPointer = &num2;
cout << "The value of num2 is " << num2 << endl;
*intPointer /= 2;
cout << "The value of num after *intPointer /= 2 is " << *intPointer << endl;
return 0;
}
Pointers to Class Members
#include <iostream>
using namespace std;
class MyClass {
public:
MyClass(int i) {
val=i;
}
int val;
int doubleValue() {
return val+val;
}
};
int main()
{
int MyClass::*data;
int (MyClass::*func)();
MyClass myObject1(1), myObject2(2);
data = &MyClass::val;
func = &MyClass::doubleValue;
cout << "Here are values: ";
cout << myObject1.*data << " " << myObject2.*data << "\n";
cout << "Here they are doubled: ";
cout << (myObject1.*func)() << " ";
cout << (myObject2.*func)() << "\n";
return 0;
}
Prints the values and addresses of variables.
#include <iostream>
using namespace std;
int var, *ptr;
int main()
{
var = 100;
ptr = &var;
cout << " Value of var: " << var << " Address of var: " << &var
<< endl;
cout << " Value of ptr: " << ptr << " Address of ptr: " << &ptr
<< endl;
return 0;
}
Returning a pointer
#include <iostream>
#include <string>
#include <vector>
using namespace std;
//returns a pointer to a string element
string* ptrToElement(vector<string>* const pVec, int i);
int main()
{
vector<string> v;
v.push_back("A");
v.push_back("B");
v.push_back("C");
cout << *(ptrToElement(&v, 0)) << endl;
string* pStr = ptrToElement(&v, 1);
cout << *pStr << endl;
string str = *(ptrToElement(&v, 2));
cout << str << endl;
*pStr = "Healing Potion";
cout << v[1] << endl;
return 0;
}
string* ptrToElement(vector<string>* const pVec, int i)
{
//returns address of the string in position i of vector that pVec points to
return &((*pVec)[i]);
}
The actual data type of the value of all pointers is the same
#include <iostream>
using namespace std;
int main ()
{
int* intPointer;
float* floatPointer;
char *charPointer;
cout << "The size of intPointer is " << sizeof(intPointer) << endl;
cout << "The size of floatPointer is " << sizeof(floatPointer) << endl;
cout << "The size of charPointer is " << sizeof(charPointer) << endl;
return 0;
}
Using a reference parameter for class type
#include <iostream>
#include <cstring>
#include <cstdlib>
using namespace std;
class StringClass {
char *p;
public:
StringClass(char *s);
~StringClass() {
delete [] p;
}
char *get() {
return p;
}
};
StringClass::StringClass(char *s)
{
int l;
l = strlen(s)+1;
p = new char [l];
if(!p) {
cout << "Allocation error\n";
exit(1);
}
strcpy(p, s);
}
// Using a reference parameter.
void show(StringClass &x)
{
char *s;
s = x.get();
cout << s << endl;
}
int main()
{
StringClass stringObject1("Hello"), stringObject2("There");
show(stringObject1);
show(stringObject2);
return 0;
}