linked list sort with variable struct selection field

MK27 · 01-17-2009, 06:49 PM

If I want to write a sort function for a linked list that can use external functions for selecting between criteria (depending on whether the criteria is alpahabetic or numeric), what's the best way to pass this "selection field" option in? In other words, if I pass a node* in as the head, how can I also pass in an option to indicate which struct member should be used in the sort?

My idea was to use a pointer to the offset of the data within the struct. I'm hoping there won't be padding that causes a problem.

Code:

typedef struct _node {
       char field1[64];
       char field2[64];
       int field3;
       struct _node *next;
} node;

node *sortfunc (node *head, int offset, int datatype) {
       node *one=head, *two=head->next;
       char *one_a, *two_a;
       int one_n, two_n;
       if (datatype==0) {
                one_i=&int(head+offset);      //  ???
                result=compnumbers(one_i,two_i);
       if (datatype==1) {
               one_a=(char*)head+offset;
               result=comparewords(one_a, two_a);

**laserlight** · 01-17-2009, 10:17 PM

Consider a predicate function like what qsort() requires.

MK27 · 01-17-2009, 10:48 PM

Quote:

Originally Posted by laserlight

Consider a predicate function like what qsort() requires.

I thought about using a function pointer, but then I would either still need the datatype parameter or else do a lot of casting with void pointers (since the compare function will be accepting either two ints or two strings) which would be ridiculuous. If I keep the datatype parameter, etc, I might as well select one or the other within the sort function (since I only have to deal with two possibilities). In fact I suppose even using a separate function to compare two ints is unnecessary.

Using an offset for the data field is easy enough for both me and the compiler. I was just wondering if there was another way.

01-17-2009, 06:49 PM	#1
MK27 subminimalist Join Date: Jul 2008 Location: NYC Posts: 3,944	linked list sort with variable struct selection field If I want to write a sort function for a linked list that can use external functions for selecting between criteria (depending on whether the criteria is alpahabetic or numeric), what's the best way to pass this "selection field" option in? In other words, if I pass a node* in as the head, how can I also pass in an option to indicate which struct member should be used in the sort? My idea was to use a pointer to the offset of the data within the struct. I'm hoping there won't be padding that causes a problem. Code: typedef struct _node { char field1[64]; char field2[64]; int field3; struct _node next; } node; node sortfunc (node head, int offset, int datatype) { node one=head, two=head->next; char one_a, two_a; int one_n, two_n; if (datatype==0) { one_i=&int(head+offset); // ??? result=compnumbers(one_i,two_i); if (datatype==1) { one_a=(char)head+offset; result=comparewords(one_a, two_a); __________________ Accuracy and integrity mean nothing if you don't make it past the censors...PYTHAGORAS Last edited by MK27; 01-17-2009 at 06:58 PM.
MK27 is offline

01-17-2009, 10:17 PM	#2
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,364	Consider a predicate function like what qsort() requires. __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
laserlight is online now

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Concatenating in linked list	drater	C Programming	12	05-02-2008 11:10 PM
singly linked circular list	DarkDot	C++ Programming	0	04-24-2007 08:55 PM
airport Log program using 3D linked List : problem reading from file	gemini_shooter	C Programming	3	03-04-2005 02:46 PM
Binary Search Trees Part III	Prelude	A Brief History of Cprogramming.com	16	10-02-2004 03:00 PM
How can I traverse a huffman tree	carrja99	C++ Programming	3	04-28-2003 05:46 PM