Passing and Assigning New Value to Pointer C++

Question

I\'m passing a pointer to a function. I\'d like to assign a new address to the passed pointer inside the function, and I\'d like that address to be used after the function retu

Answer 1

Pass a reference to the pointer:

void foo( int *& fooPtr, int & newInt )

The reason why your method does not work is that you're passing the pointer by-value. Passing by-value creates a temporary within the function, so as soon as the function returns, any changes to the temporary go away.

It is no different than this:

void foo(int x)
{
   x = 10;
}

int main()
{
   int a = 0;
   foo( a );
   // a is still 0, not 10
}

The a is passed by value, so the foo() function changes the parameter to 10 within the function. However, you will see that a in main does not change to 10 after the function returns.

To change a, you need to pass the int by reference:

void foo(int& x)
{
   x = 10;
}

int main()
{
   int a = 0;
   foo( a );
   // a is now 10
}

Answer 2

Pass a pointer of the pointer and assign to it

int main()
{
    int i = 100, j = 200;
    int * intPtr = &i;
    foo( &intPtr, j );
    //  I want intPtr to point to j, which contains 200 after returning from foo.
}

void foo( int ** fooPtr, int & newInt )
{
    int * newIntPtr = newInt;
    *fooPtr = newIntPtr;
}

Answer 3

If you programing in pure C you can do like this

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void foo(int **, int *);


 int main()
{
  int i = 100, j = 200;
  int * intPtr = &i;
  int  *intPtr2=&j;
  foo( &intPtr, intPtr2 );
  //  I want intPtr to point to j, which contains 200 after returning   from foo.
  printf("%d",*intPtr);
}
 void foo( int ** fooPtr, int * newInt )
{
  int * newIntPtr = newInt;

  *fooPtr = newIntPtr; 
}