C++ Tutorial/Function/function pointers

arguments passed by pointer

<source lang="cpp">#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;            
 }</source>

arguments passed by reference

<source lang="cpp">#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;                  
 }</source>

array passed by pointer

<source lang="cpp">#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; 
 }</source>

Arrays of pointers to functions

<source lang="cpp">#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;
}</source>

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

<source lang="cpp">#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;

}</source>

5"

orders two arguments using pointers

<source lang="cpp">#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;  
    }  
 }</source>

sorts an array using pointers

<source lang="cpp">#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;  
    }  
 }</source>

Use function pointers as a function parameter

<source lang="cpp">#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;
}</source>

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

<source lang="cpp">#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;
}</source>

x: 1 y: 2
x: 2 y: 1

Using function pointers

<source lang="cpp">#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;
}</source>

x: 1 y: 2