CODEWITHSUNDEEP
c++c++11
Mostafa Talebi
Mostafa Talebi

Reputation: 9183

C++ Comparing Two Integer Values, one simple and one pointer

I have the following function in c++:

bool compareThem(int top_limit, int* maximum)
{
       if( top_limit >= maximum )
       {
            cout << "Error, maximum number shown be greater than top_limit.";
       }
}

I want a simple comparison between the integer and integer pointer, though, logically C++ cannot do it, since with == operator, int and int* are not of the same type. How should I then solve it?

Upvotes: 2

Views: 3679

Answers (3)

ilent2
ilent2

Reputation: 5241

In C/C++ you can use the * and the & operators to access the value pointed to by an address (pointer) and acquire the address in memory of a value. In your example you try to compare an integer with a pointer, there are a couple of ways I can think of that you might do this (depending on the desired behaviour):

Compare the integer with the value pointed to by the pointer

In order to compare the values of the two objects you need to retrieve the value of the address pointed to by the pointer. To do this you need to use the dereference operator to retrieve the value which you can then treat as an integer, consider the following.

bool myFunction(int a, int* pointer_to_b)
{
  int b = *pointer_to_b;
  return a > b;
  // Or the one line: return a > *pointer_to_b;
}

Compare the address of the pointer to an integer

Since addresses are just integers it is possible to compare a integer to the address stored in a pointer however you should avoid doing this sort of thing unless you really need to. Consider:

bool myBadFunction(int a, int* b)
{
  return (int*) a > b;
}

Compare the address of the integer to the address stored in the pointer

I've rarely encountered comparison of an integer to the address of an integer but I have on occasion encountered code comparing the address of a vale to a specific address (but there are usually alternatives and I don't recommend it). For how you might achieve this see the following.

bool myAlmostUselessFunction(int a, int* b)
{
  int *address_of_a = &a;     //< take the address of a
  return address_of_a > b;
}

Upvotes: 1

marcinj
marcinj

Reputation: 50006

What this code does

bool compareThem(int top_limit, int* maximum)
{
       if( top_limit >= maximum )

is comparing top_limit integer value, with address inside maximum pointer variable. To get value of variable to which pointer points, you must dereference pointer variable, which is done with * operator: *maximum.

Upvotes: 3

TartanLlama
TartanLlama

Reputation: 65630

Just dereference maximum:

if (top_limit >= *maximum)
//               ^

This will compare the int top_limit with the int stored at the memory location pointed to by maximum.

This is one of the fundamentals of C++ and should be covered in your introductory book.

Upvotes: 7

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