C Macro Swap Function - Topic

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Mar 23 2014 01:49pm

I've been stuck with this problem forever, its a fill in the blank:

#define Swap____ {\
int ______;\
int ______;\
\
_______;\
_______;\
}

It's supposed to be kind of call by reference swap function..

Minkomonster

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Mar 23 2014 02:13pm

Code

#define Swap(x,y){ int t;t=x;x=y;y=t; }

This post was edited by Minkomonster on Mar 23 2014 02:16pm

killedbyz

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Mar 23 2014 02:45pm

Quote (Minkomonster @ Mar 23 2014 01:13pm)

Code

#define Swap(x,y){ int t;t=x;x=y;y=t; }

That would be a pass value, so it doesn't work

Minkomonster

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Mar 23 2014 03:01pm

Quote (killedbyz @ Mar 23 2014 03:45pm)

That would be a pass value, so it doesn't work

Its a pre processor directive. It isn't going to pass by reference regardless. But if you really want it pass by reference then you can do

Code

#define Swap(x,y){ int t;t=*x;*x=*y;*y=t; }

This post was edited by Minkomonster on Mar 23 2014 03:02pm

killedbyz

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Mar 25 2014 07:23pm

I think I know what it means. Here's the problem with that macro..

Say you're swapping index with array[index]
then the swap substitution would be:
int temp = (index); (index) = (array[index]); (a[index]) = __swapTemp

On the first operation index is changed, so when used on the second one it produces a bug

Muted

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Mar 25 2014 09:05pm

Quote (killedbyz @ 23 Mar 2014 14:49)

Trick question!

#define Swap(a, b, c)

Princess

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Mar 25 2014 09:13pm

Code

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

#define SwapPointer(x, y){ int t; t=*x; *x=*y; *y=t; }
#define SwapXOR(x, y) { x^=y; y^=x; x^=y; }
#define SwapNormal(x, y) { int t; t=x; x=y; y=t; }

int main()
{
int array[2] = {1, 2};

printf("Original:\t%d\t%d\n", array[0], array[1]);

SwapPointer(&array[0], &array[1]);

printf("Pointer:\t%d\t%d\n", array[0], array[1]);

SwapXOR(array[0], array[1]);

printf("XOR:\t\t%d\t%d\n", array[0], array[1]);

SwapNormal(array[0], array[1]);

printf("Normal:\t\t%d\t%d\n", array[0], array[1]);

return 0;
}

----------
Output
----------

Original: 1 2
Pointer: 2 1
XOR: 1 2
Normal: 2 1

Process returned 0 (0x0) execution time : 0.033 s
Press any key to continue.

What is the problem you hare having? I don't see the a bug in his code. How are you attempting to use this? Show us your code...

killedbyz

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Mar 25 2014 11:38pm

Quote (Princess @ Mar 25 2014 08:13pm)

Code

What is the problem you hare having? I don't see the a bug in his code. How are you attempting to use this? Show us your code...

The problem would be when doing something like

int main() {
int index = 1;
int array[2] = {55, 43};

swap(index, array[index]);
}

This post was edited by killedbyz on Mar 25 2014 11:39pm

Minkomonster

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Mar 26 2014 02:33am

Quote (killedbyz @ Mar 26 2014 12:38am)

The problem would be when doing something like

int main() {
int index = 1;
int array[2] = {55, 43};

swap(index, array[index]);
}

Think about what you are trying to do...

This post was edited by Minkomonster on Mar 26 2014 02:57am

SelfTaught

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#10

Mar 29 2014 11:36am

nvm

This post was edited by SelfTaught on Mar 29 2014 11:37am

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