C++ Tutorial/Function/function pointers

Материал из C\C++ эксперт
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arguments passed by pointer

#include <iostream>  
  using namespace std;  
    
  int main(){  
     void centimize(double*);  
    
     double var = 10.0;        
     cout << "var = " << var << " inches" << endl;  
    
     centimize(&var);          
     cout << "var = " << var << " centimeters" << endl;  
     return 0;  
  }  
  void centimize(double* ptrd){  
     *ptrd *= 2.54;            
  }

arguments passed by reference

#include <iostream>  
  using namespace std;  
    
  int main(){  
     void centimize(double&);    
    
     double var = 10.0;          
     cout << "var = " << var << " inches" << endl;  
    
     centimize(var);             
     cout << "var = " << var << " centimeters" << endl;  
     return 0;  
  }  
  void centimize(double& v){  
     v *= 2.54;                  
  }

array passed by pointer

#include <iostream>  
  using namespace std;  
  const int MAX = 5;     
    
  int main(){  
     void centimize(double*);
    
     double varray[MAX] = { 10.0, 43.1, 95.9, 59.7, 87.3 };  
    
     centimize(varray);      
    
     for(int j=0; j<MAX; j++)
        cout << "varray[" << j << "]=" << varray[j] << " centimeters" << endl;  
     return 0;  
    }  
  void centimize(double* ptrd){  
     for(int j=0; j<MAX; j++)  
        *ptrd++ *= 2.54; 
  }

Arrays of pointers to functions

#include <iostream>
 
 void Square (int&,int&);
 void Cube (int&, int&);
 void Swap (int&, int &);
 void GetVals(int&, int&);
 void PrintVals(int, int);
 
 int main()
 {
     int valOne=1, valTwo=2;
     int i;
     const int MaxArray = 5;
     void (*pFuncArray[MaxArray])(int&, int&);
 
     pFuncArray[0] = GetVals; 
     pFuncArray[1] = Square; 
     pFuncArray[2] = Cube; 
     pFuncArray[3] = Swap; 
     pFuncArray[4] = Square; 
 
     for (i=0;i<MaxArray; i++)
     {
         pFuncArray[i](valOne,valTwo);
         PrintVals(valOne,valTwo);
     }
     return 0;
 }
 
 void PrintVals(int x, int y)
 {
     std::cout << "x: " << x << " y: " << y << std::endl;
 }
 
 void Square (int & rX, int & rY)
 {
     rX *= rX;
     rY *= rY;
 }
 
 void Cube (int & rX, int & rY)
 {
     int tmp;
 
     tmp = rX;
     rX *= rX;
     rX = rX * tmp;
 
     tmp = rY;
     rY *= rY;
     rY = rY * tmp;
 }
 
 void Swap(int & rX, int & rY)
 {
     int temp;
     temp = rX;
     rX = rY;
     rY = temp;
 }
 
 void GetVals (int & rValOne, int & rValTwo)
 {
     std::cout << "New value for ValOne: ";
     std::cin >> rValOne;
     std::cout << "New value for ValTwo: ";
     std::cin >> rValTwo;
 }
New value for ValOne: 1
New value for ValTwo: 2
x: 1 y: 2
x: 1 y: 4
x: 1 y: 64
x: 64 y: 1
x: 4096 y: 1

Function pointer for overloaded function

#include <iostream>
using namespace std;
int myfunc(int a);
int myfunc(int a, int b);
int main()
{
  int (*fp)(int a); // pointer to int f(int)
  //int (*fp)(int a, int b);
  fp = myfunc; // points to myfunc(int)
  cout << fp(5);
  return 0;
}
int myfunc(int a)
{
  return a;
}
int myfunc(int a, int b)
{
  return a*b;
}
5"

orders two arguments using pointers

#include <iostream>  
  using namespace std;  
    
  int main(){  
     void order(int*, int*); 
    
     int n1=99, n2=11;       
     int n3=22, n4=88;  
    
     order(&n1, &n2);        
     order(&n3, &n4);  
    
     cout << "n1=" << n1 << endl;  
     cout << "n2=" << n2 << endl;  
     cout << "n3=" << n3 << endl;  
     cout << "n4=" << n4 << endl;  
     return 0;  
    }  
  void order(int* numb1, int* numb2){  
     if(*numb1 > *numb2){  
        int temp = *numb1;          
        *numb1 = *numb2;  
        *numb2 = temp;  
     }  
  }

sorts an array using pointers

#include <iostream>  
  using namespace std;  
    
  int main(){  
     void bsort(int*, int);    
     const int N = 10;         
     int arr[N] = { 37, 84, 62, 91, 11, 65, 57, 28, 19, 49 };  
    
     bsort(arr, N);  
    
     for(int j=0; j<N; j++)  
        cout << arr[j] << " ";  
     cout << endl;  
     return 0;  
    }  
  void bsort(int* ptr, int n){  
     void order(int*, int*); 
     int j, k;               
    
     for(j=0; j<n-1; j++)    
        for(k=j+1; k<n; k++) 
           order(ptr+j, ptr+k);
    }  
  void order(int* numb1, int* numb2){  
     if(*numb1 > *numb2){  
        int temp = *numb1;
        *numb1 = *numb2;  
        *numb2 = temp;  
     }  
  }

Use function pointers as a function parameter

#include <iostream>
 using namespace std; 
 
 void Square (int&,int&);
 void Cube (int&, int&);
 void Swap (int&, int &);
 void GetVals(int&, int&);
 void PrintVals(void (*)(int&, int&),int&, int&);
 
 int main()
 {
     int valOne=1, valTwo=2;
     void (*pFunc)(int&, int&);
 
     pFunc = GetVals; 
     PrintVals ( pFunc, valOne, valTwo);
     pFunc = Square; 
     PrintVals ( pFunc, valOne, valTwo);
     pFunc = Cube; 
     PrintVals ( pFunc, valOne, valTwo);
     pFunc = Swap; 
     PrintVals ( pFunc, valOne, valTwo);
 
     return 0;
 }
 
 void PrintVals( void (*pFunc)(int&, int&),int& x, int& y)
 {
     cout << "x: " << x << " y: " << y << endl;
     pFunc(x,y);
     cout << "x: " << x << " y: " << y << endl;
 }
 
 void Square (int & rX, int & rY)
 {
     rX *= rX;
     rY *= rY;
 }
 
 void Cube (int & rX, int & rY)
 {
     int tmp;
 
     tmp = rX;
     rX *= rX;
     rX = rX * tmp;
 
     tmp = rY;
     rY *= rY;
     rY = rY * tmp;
 }
 
 void Swap(int & rX, int & rY)
 {
     int temp;
     temp = rX;
     rX = rY;
     rY = temp;
 }
 
 void GetVals (int & rValOne, int & rValTwo)
 {
     cout << "New value for ValOne: ";
     cin >> rValOne;
     cout << "New value for ValTwo: ";
     cin >> rValTwo;
 }
x: 1 y: 2
New value for ValOne: 1
New value for ValTwo: 2
x: 1 y: 2
x: 1 y: 2
x: 1 y: 4
x: 1 y: 4
x: 1 y: 64
x: 1 y: 64
x: 64 y: 1

Use typedef to define a function type for function pointer

#include <iostream>
 using namespace std;
 
 void Square (int&,int&);
 void Cube (int&, int&);
 void Swap (int&, int &);
 void GetVals(int&, int&);
 
 typedef  void (*VPF) (int&, int&) ;
 void PrintVals(VPF,int&, int&);
 
 int main()
 {
     int valOne=1, valTwo=2;
     VPF pFunc;
 
     pFunc = GetVals;
     pFunc = Square;
     pFunc = Cube;
 
     pFunc = Swap;
  
     PrintVals ( pFunc, valOne, valTwo);
     return 0;
 }
 
 void PrintVals( VPF pFunc,int& x, int& y)
 {
     cout << "x: " << x << " y: " << y << endl;
     pFunc(x,y);
     cout << "x: " << x << " y: " << y << endl;
 }
 
 void Square (int & rX, int & rY)
 {
     rX *= rX;
     rY *= rY;
 }
 
 void Cube (int & rX, int & rY)
 {
     int tmp;
 
     tmp = rX;
     rX *= rX;
     rX = rX * tmp;
 
     tmp = rY;
     rY *= rY;
     rY = rY * tmp;
 }
 
 void Swap(int & rX, int & rY)
 {
     int temp;
     temp = rX;
     rX = rY;
     rY = temp;
 }
 
 void GetVals (int & rValOne, int & rValTwo)
 {
     cout << "New value for ValOne: ";
     cin >> rValOne;
     cout << "New value for ValTwo: ";
     cin >> rValTwo;
 }
x: 1 y: 2
x: 2 y: 1

Using function pointers

#include <iostream>
 
 void Square (int&,int&);
 void Cube (int&, int&);
 void Swap (int&, int &);
 void PrintVals(int, int);
 
 int main()
 {
     void (* pFunc) (int &, int &);
     int valOne=1, valTwo=2;
     PrintVals(valOne, valTwo);
     pFunc(valOne, valTwo);
     PrintVals(valOne, valTwo);
     pFunc = Square; 
     PrintVals(valOne, valTwo);
     pFunc(valOne, valTwo);
     PrintVals(valOne, valTwo);
     pFunc = Cube; 
     PrintVals(valOne, valTwo);
     pFunc(valOne, valTwo);
     PrintVals(valOne, valTwo);
     pFunc = Swap; 
     PrintVals(valOne, valTwo);
     pFunc(valOne, valTwo);
     PrintVals(valOne, valTwo);
     
     return 0;
 }
 
 void PrintVals(int x, int y)
 {
     std::cout << "x: " << x << " y: " << y << std::endl;
 }
 
 void Square (int & rX, int & rY)
 {
     rX *= rX;
     rY *= rY;
 }
 
 void Cube (int & rX, int & rY)
 {
     int tmp;
 
     tmp = rX;
     rX *= rX;
     rX = rX * tmp;
 
     tmp = rY;
     rY *= rY;
     rY = rY * tmp;
 }
 
 void Swap(int & rX, int & rY)
 {
     int temp;
     temp = rX;
     rX = rY;
     rY = temp;
 }
x: 1 y: 2
Источник — «http://cppe.ru/index.php?title=C%2B%2B_Tutorial/Function/function_pointers&oldid=2482»