Thread: count no of characters

Code:

// Ex4_10.cpp
// Counting string characters using a pointer
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

int main()
{
   const int MAX = 80;                 // Maximum array dimension
   char buffer[MAX];                   // Input buffer
   char* pbuffer = buffer;             // Pointer to array buffer

   cout << endl                        // Prompt for input
        << "Enter a string of less than "
        << MAX << " characters:"
        << endl;

   cin.getline(buffer, MAX, '\n');     // Read a string until \n

   while(*pbuffer)                     // Continue until \0
      pbuffer++;


   cout << "\nAddress of pbuffer: " << reinterpret_cast<size_t>(&pbuffer);
   cout << "\nAddress of buffer: " << reinterpret_cast<size_t>(&buffer) << endl;

   cout << "\n\nAddress of pbuffer: " << &pbuffer;
   cout << "\nAddress of buffer: " << &buffer << endl;
   

   cout << endl
        << "The string \"" << buffer
        << "\" has " << pbuffer - buffer << " characters.";
   cout << endl;
   return 0;
}

How does this count the number of characters ? its the code from a book which I'm reading, although I have added few statements in this

Well pbuffer would be pointing at the last character after the while loop which I think is the null character ('\0')

While buffer is pointing at the first element in the array

So its simple that its difference would produce the number of characters,

I checked its address and on my pc it produced

the following

pbuffer = 1244920
buffer = 1244932

in hex

pbuffer = 0012FEF8
buffer = 0012FF04


so by manual calc of the above values their difference is 12, Right ?

But when used in the cout << statement its not the same ?

how ?

Strange, as the posted code works OK for me:

Code:

Enter a string of less than 80 characters:
Hello, World!
Address of buffer: 2293520
Address of pbuffer: 2293516
The string "Hello, World!" has 13 characters.

--
Mats

Well what I meant is that the difference between the addresses

2293516 - 2293520 = -4

then how is it showing 13 in the cout statement


sorry but i think im not able to express what i want to say, so please state if you didn't get the point

Ehm, in the original code you had:

Code:

   cout << "Address of buffer: " << reinterpret_cast<size_t>(&buffer) << endl;
   cout << "Address of pbuffer: " << reinterpret_cast<size_t>(&pbuffer);

If you remove the &, you will get more sane results:

Code:

Enter a string of less than 80 characters:
12345
Address of buffer: 2293520
Address of pbuffer: 2293525
The string "12345" has 5 characters.

--
Mats

Actually, it won't print the character - it would print the STRING it's pointing to.

As to how you get the address - you would have to cast it somehow if you use cout >> to get the value of a char pointer - you could for example cast it to another pointer [void * would be my choice].

--
Mats

Originally Posted by manzoor

Ok it prints the string its pointing to

how to get the address of that string without using the reinterpret_cast

Sorry, I was editing my reply whilst you were writing this one. You have to cast it some way or another - that's because operator>>(ostream &os, const char *) is defined to print a string - all other operator>>(ostream &os, T *) are defined such as this:

Code:

template <typename T> ostream & operator>>(ostream &os, T *ptr)
{
     os << hex << reinterpret_cast<int_ptr_t>(ptr);
}

Edit: it's the same type of problem as if you want to print the numeric value of a char - it will print the corresponding character unless you cast it to a different type.

--
Mats