function pointer in c++ code example

Example 1: c++ pointers

#include <iostream>

using namespace std;

int main () {
   int  var = 20;   // actual variable declaration.
   int  *ip;        // pointer variable 

   ip = &var;       // store address of var in pointer variable

   cout << "Value of var variable: "; 
   cout << var << endl; //Prints "20"

   // print the address stored in ip pointer variable
   cout << "Address stored in ip variable: ";
   cout << ip << endl; //Prints "b7f8yufs78fds"

   // access the value at the address available in pointer
   cout << "Value of *ip variable: ";
   cout << *ip << endl; //Prints "20"

   return 0;
}

Example 2: pointers in cpp

#include <iostream>
using std::cout;

int main() {
  /* 
  Some things to keep in mind:
  	-you shouldn't circumvent the type system if you are creating raw ptrs
  	and don't need to "type pun" or cast (don't use void ptrs)
    -ptr types only reference memory (which are integers), not actual data, thus
    they should not be treated as data types
    char* is just 1 byte of mem, int* is just 4 bytes of mem, etc
    - '*' means that you are creating a pointer which "points" to the mem address
    of a variable
    - '&', in this case, means "get the mem address of this variable"
  */
  
  void* ptr; // a pointer that doesn't reference a certain size of memory
  int* int_ptr; // a pointer that points to data with
  				// only 4 bytes of memory (on stack)
  
  int a = 5; // allocates 4 bytes of mem and stores "5" there (as a primitive)
  ptr = &a; // can only access the memory address of 'a' (not the data there)
  
  int b = 45; 
  int_ptr = &b; // can access both memory address and data of 'b'
  
  cout << ptr << "\n"; // prints mem address of 'a'
  /*cout << *ptr << "\n"; <- this will error out; a void ptr cannot be 
  							 derefrenced */
  cout << *(int*)ptr << "\n"; // type punning to get around void ptr (extra work)
  
  cout << int_ptr << "\n"; // mem address of b
  cout << *int_ptr << "\n"; // data stored at b
  
  /* -- OUTPUTS -- */
  /*
  	some memory address (arbitrary) which contains 05 00 00 00 as its data
  	5
    some memory address (arbitrary) which contains 2D 00 00 00 as its data
    45
  */
  
  return 0; // you only need this if "main" isnt the linker entry point
  			// you also don't care
  
  // ur also probably wondering why I didn't using namespace std... cherno
}

Example 3: pointer in c++

int* pointVar, var;
var = 5;

// assign address of var to pointVar
pointVar = &var;

// access value pointed by pointVar
cout << *pointVar << endl;   // Output: 5

In the above code, the address of var is assigned to the pointVar pointer.
We have used the *pointVar to get the value stored in that address.

Example 4: Function pointer C++

void one() { cout << "One\n"; }
void two() { cout << "Two\n"; }


int main()
{
	void (*fptr)(); //Declare a function pointer to voids with no params

	fptr = &one; //fptr -> one
	*fptr(); //=> one()

	fptr = &two; //fptr -> two
	*fptr(); //=> two()

	return 0;
}

Example 5: c function pointer

//Declaration of a pointer to a function that takes an integer 
//and returns an integer.
int (*f_ptr)(int);

//Assignment of a function foo to the function pointer f_ptr declared above.
f_ptr = foo;

//Calling foo indirectly via f_ptr, passing the return value of foo to r.
int r = f_ptr(v);

//Assigning an address of a function to the function pointer f_ptr,
//then calling foo by dereferencing the function pointer.  
f_ptr = &foo;
int r = (*f_ptr)(v);

Example 6: pointers c++

baz = *foo;