Swap call by reference confusion Post: 302889313

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Top Forums Programming Swap call by reference confusion Post 302889313 by yifangt on Thursday 20th of February 2014 12:38:43 AM

02-20-2014

Registered User

While I was reading more about pointer in C, I came up another silly question for the same "call-by-reference swap example" here.

Code:

#include <stdio.h>

void swap1 (int *x, int *y);

int main ()
{
  int a, b;
  a = 10; 
  b = 20;
  printf ("Original a = %d    b = %d\n", a, b);
  swap1 (&a, &b);
  printf ("After calling swap1, a = %d b = %d\n", a, b);
  return 0;
}

void swap1 (int *x, int *y)         //Compiled without error but did not work!
{
  int t;
  t = *x;
  x = y;           // Line 23 Correct way is *x = *y; 
  y = &t;           //Line 24 Correct way is *y = t; I was thinking the address should work too.
}

Code:

$> ./a.out
Original a = 10    b = 20
After calling swap1, a = 10 b = 20

I thought Line 23 is to assign the "address of x" with "the address of y" and then Line 24, makes y pointing to t, so that the addresses exchanged. Why my understanding is wrong?
Or, what is the difference between "x = y" and "*x = *y" from memory perspective? Thanks a lot!

yifangt

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colors

COLORS(3)						   libbash colors Library Manual						 COLORS(3)

NAME

     colors -- libbash library for setting tty colors.

SYNOPSIS

     colorSet	  <color>
     colorReset
     colorPrint   [<indent>] <color> <text>
     colorPrintN  [<indent>] <color> <text>

DESCRIPTION

   General
     colors is a collection of functions that make it very easy to put colored text on tty.

     The function list:
	   colorSet	    Sets the color of the prints to the tty to COLOR
	   colorReset	    Resets current tty color back to normal
	   colorPrint	    Prints TEXT in the color COLOR indented by INDENT (without adding a newline)
	   colorPrintN	    The same as colorPrint, but trailing newline is added

     Detailed interface description follows.

   Available colors:
	   Green
	   Red
	   Yellow
	   White
     The color parameter is non-case-sensitive (i.e. RED, red, ReD, and all the other forms are valid and are the same as Red).

FUNCTIONS DESCRIPTIONS

   colorSet <color>
     Sets the current printing color to color.

   colorReset
     Resets current tty color back to normal.

   colorPrint [<indent>] <color>
     Prints text using the color color indented by indent (without adding a newline).

     Parameters:

       <indent>
	 The column to move to before start printing.  This parameter is optional. If ommitted - start output from current cursor position.

       <color>
	 The color to use.

       <color>
	 The text to print.

   colorPrintN [<indent>] <color>
     The same as colorPrint, except a trailing newline is added.

EXAMPLES

     Printing a green 'Hello World' with a newline:

	  Using colorSet:
		  $ colorSet green
		  $ echo 'Hello World'
		  $ colorReset

	  Using colorPrint:
		  $ colorPrint 'Hello World'; echo

	  Using colorPrintN:
		  $ colorPrintN 'Hello World'

AUTHORS

     Hai Zaar <haizaar@haizaar.com>
     Gil Ran <gil@ran4.net>

SEE ALSO

     ldbash(1), libbash(1)

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