"Function pointer C++" Code Answer's
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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;
}
Source: www.tutorialspoint.com
pointer in c++
// Variable is used to store value
int a = 5;
cout << a; //output is 5
// Pointer is used to store address of variable
int a = 5;
int *ab;
ab = &a; //& is used get address of the variable
cout << ab; // Output is address of variable
what is this pointer in c++
Every object in C++ has access to its own address through an important pointer called this pointer.
The this pointer is an implicit parameter to all member functions.
Therefore, inside a member function,
this may be used to refer to the invoking object.
Friend functions do not have a this pointer,
because friends are not members of a class.
Only member functions have a this pointer.
Source: www.tutorialspoint.com
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
}
c++ pointers
#include <iostream>
using namespace std;
// isualize this on http://pythontutor.com/cpp.html#mode=edit
int main()
{
double* account_pointer = new double;
*account_pointer = 1000;
cout << "Allocated one new variable containing " << *account_pointer
<< endl;
cout << endl;
int n = 10;
double* account_array = new double[n];
for (int i = 0; i < n; i++)
{
account_array[i] = 1000 * i;
}
cout << "Allocated an array of size " << n << endl;
for (int i = 0; i < n; i++)
{
cout << i << ": " << account_array[i] << endl;
}
cout << endl;
// Doubling the array capacity
double* bigger_array = new double[2 * n];
for (int i = 0; i < n; i++)
{
bigger_array[i] = account_array[i];
}
delete[] account_array; // Deleting smaller array
account_array = bigger_array;
n = 2 * n;
cout << "Now there is room for an additional element:" << endl;
account_array[10] = 10000;
cout << 10 << ": " << account_array[10] << endl;
delete account_pointer;
delete[] account_array; // Deleting larger array
return 0;
}
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;
}
Source: www.dev-hq.net
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