Hi All,
Here I have a linked list each containing a char and is double linked.
Then I have a pointer to an item in that list which is the current
insertion point.
In this funtion, the user hits the right
and left keys to move this insertion point (cursor)
Here is the problem:
But its not stable, the insertion point seems to skip an item
back, here and there. It could be the API Im using for the keyboard
input but Im not sure.
Thanks in advance for any help.
John
//a char structure, making a text string list
struct Word{
char *c;
struct Word *next,*back;
};
typedef struct Word Word;
Word *wrd;// a linked list of Word structures
Word *insert;// pointer to the current insertion point of *wrd
wrd = (allocate a list of Word structures)
insert = (pointer to an insertion point in the text in the *wrd list)
DoKey(insert,RI GHT_KEY);
/* etc */
void DoKey(struct Word *char_insert, int key){
switch(key){
case RIGHT_KEY:
if(char_insert->next!=NULL)
char_insert=cha r_insert->next;/* this is not fool proof,
any help? */
break;
case LEFT_KEY:
if(char_insert->back!=NULL)
char_insert=cha r_insert->back;/* this is not fool proof,
any help? */
break;
}
}
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et 5 6061
[Followups set to comp.lang.c - nothing personal, Seebs!]
John N. wrote: Hi All,
Here I have a linked list each containing a char and is double linked.
Your code says char *, not char.
Then I have a pointer to an item in that list which is the current insertion point.
<...> But its not stable, the insertion point seems to skip an item back, here and there. It could be the API Im using for the keyboard input but Im not sure.
It's your misunderstandin g of pointers, I'm afraid.
//a char structure, making a text string list
If you have a C99 compiler, // is legal comment syntax. Do you?
struct Word{ char *c; struct Word *next,*back; }; typedef struct Word Word;
Word *wrd;// a linked list of Word structures Word *insert;// pointer to the current insertion point of *wrd
wrd = (allocate a list of Word structures)
This ain't gonna compile.
insert = (pointer to an insertion point in the text in the *wrd list)
Nor is this. Please remember, when posting code here, that by definition you
do not know where the problem is. So it's not a good idea to chop out
random chunks of it when asking for help.
DoKey(insert,RI GHT_KEY);
/* etc */
void DoKey(struct Word *char_insert, int key){ switch(key){ case RIGHT_KEY: if(char_insert->next!=NULL) char_insert=cha r_insert->next;/* this is not fool proof, any help? */
C is pass-by-value.
void DoKey(struct Word **char_insert, int key)
{
switch(key)
{
case RIGHT_KEY:
if((*char_inser t)->next != NULL)
{
*char_insert = (*char_insert)->next;
}
break;
case LEFT_KEY:
if((*char_inser t)->back != NULL)
{
*char_insert = (*char_insert)->back;
}
break;
default:
/* unhandled key event */
break;
}
}
--
Richard Heathfield : bi****@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
John N. wrote: Here I have a linked list each containing a char and is double linked. Then I have a pointer to an item in that list which is the current insertion point.
In this function, the user hits the right and left keys to move this insertion point (cursor)
Here is the problem:
But its not stable, the insertion point seems to skip an item back, here and there. It could be the API Im using for the keyboard input but Im not sure.
No, it isn't likely to be that.
Thanks in advance for any help. John
//a char structure, making a text string list struct Word{ char *c; struct Word *next,*back; }; typedef struct Word Word;
Word *wrd;// a linked list of Word structures Word *insert;// pointer to the current insertion point of *wrd
wrd = (allocate a list of Word structures)
And how is this data structure initialized? Zero pointers, or
pointers to itself (a circular list)? Or are you allocating and
initializing a whole bunch of Word structures, and putting them into a
valid linked list?
insert = (pointer to an insertion point in the text in the *wrd list)
So, presumably this is a contraction for 'insert = wrd;'? If not, you
need to show the initialization, since without the initialization, it
is hard to tell what the heck you might be doing.
DoKey(insert,RI GHT_KEY);
You've not shown where the character is coming from. I know you said
the keyboard, but which variable contains the value? Or is the
'RIGHT_KEY' -- presumably a macro since it is in upper case -- the
value purportedly to be inserted?
/* etc */
void DoKey(struct Word *char_insert, int key){ switch(key){ case RIGHT_KEY: if(char_insert->next!=NULL) char_insert=cha r_insert->next;/* this is not fool proof, any help? */ break;
With a doubly-linked list, when you insert a new node, you allocate
the new node and populate the data portion (c) with the data for the
node. Then, assuming that the new node is inserted after the
insertion point, you ensure that the next pointer of the new node
points to the node that the insertion point points to as the next
node, that the back pointer of the next node points to the new node,
that the back pointer of the new node points to where the back pointer
of the insertion pointer points, and the next pointer of the back node
points to the new node. You might or might not also adjust the
insertion point. The sequence is similar but different if the new
node goes before the insertion point.
You've not shown very much of any of this material. You don't
allocate new nodes and you don't fix up the pre-existing nodes.
case LEFT_KEY: if(char_insert->back!=NULL) char_insert=cha r_insert->back;/* this is not fool proof, any help? */ break; } }
Any more help? Draw a diagram! Draw a lot of diagrams! And make
sure all your pointers are initialized.
Finally, a member 'char *c' is misleading (but not, I hasten to
emphasize, wrong). In general, a variable c is a single character,
not a pointer to a character. There are various possible names that
would be happier choices - s or p are primary options, and there are a
myriad others. From the code you show, it is impossible to deduce
whether you store pointers to null-terminated strings or pointers to
single characters in it - you don't show it being used at all, in fact.
Given your problem description, you might be better off using c as a
simple char - though a doubly linked list of single characters is an
incredibly heavy-weight structure (typically occupying 12 bytes per
character).
Another reading of your problem might be that you are wondering why
the value of 'insert' in the calling code is not modified by the code
in DoKey -- and the answer is because you don't pass insert as a
pointer to a Word pointer. This only applies if you are already sure
you've built your doubly-linked list correctly, which is (as far as
anyone can see) debatable.
--
Jonathan Leffler #include <disclaimer.h >
Email: jl******@earthl ink.net, jl******@us.ibm .com
Guardian of DBD::Informix v2003.04 -- http://dbi.perl.org/
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
"John N." <st*******@yaho o.com> wrote in struct Word{ char *c; struct Word *next,*back; }; typedef struct Word Word;
Run the following function
void integrity_test( Word *head)
{
Word *prev = NULL:
printf("Start\n ");
while(head)
{
printf("%s\n", head->c);
prev = head;
head = head->next;
}
printf("End\n") ;
while(prev)
{
printf("%s\n", prev->c);
prev = prev->back;
}
}
This should expose problems with the linked list structure.
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
On 28 Dec 2003 06:39:31 GMT, st*******@yahoo .com (John N.) wrote: Hi All,
Here I have a linked list each containing a char and is double linked. Then I have a pointer to an item in that list which is the current insertion point.
In this funtion, the user hits the right and left keys to move this insertion point (cursor)
Here is the problem:
But its not stable, the insertion point seems to skip an item back, here and there. It could be the API Im using for the keyboard input but Im not sure.
Thanks in advance for any help. John
//a char structure, making a text string list struct Word{ char *c; struct Word *next,*back; }; typedef struct Word Word;
Word *wrd;// a linked list of Word structures Word *insert;// pointer to the current insertion point of *wrd
wrd = (allocate a list of Word structures) insert = (pointer to an insertion point in the text in the *wrd list)
DoKey(insert,R IGHT_KEY);
/* etc */
void DoKey(struct Word *char_insert, int key){ switch(key){ case RIGHT_KEY: if(char_insert->next!=NULL) char_insert=cha r_insert->next;/* this is not fool proof, any help? */ break; case LEFT_KEY: if(char_insert->back!=NULL) char_insert=cha r_insert->back;/* this is not fool proof, any help? */ break; } }
The real question is why do you think it worked at all. The
char_insert variable inside your function is not the same variable you
defined near the top of your code.
Your function performs all of its assignments to a local variable
(actually a parameter which, since C passes by value, is a copy of the
argument and not the argument itself). When the function exits, all
local variables (other than static) are destroyed. The result of your
function's assignments are never communicated back to the calling
function.
<<Remove the del for email>>
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
> >//a char structure, making a text string list struct Word{ char *c; struct Word *next,*back; }; typedef struct Word Word;
Word *wrd;// a linked list of Word structures Word *insert;// pointer to the current insertion point of *wrd
wrd = (allocate a list of Word structures) insert = (pointer to an insertion point in the text in the *wrd list)
DoKey(insert,R IGHT_KEY);
/* etc */
void DoKey(struct Word *char_insert, int key){ switch(key){ case RIGHT_KEY: if(char_insert->next!=NULL) char_insert=cha r_insert->next;/* this is not fool proof, any help? */ break; case LEFT_KEY: if(char_insert->back!=NULL) char_insert=cha r_insert->back;/* this is not fool proof, any help? */ break; } }
The real question is why do you think it worked at all. The char_insert variable inside your function is not the same variable you defined near the top of your code.
Your function performs all of its assignments to a local variable (actually a parameter which, since C passes by value, is a copy of the argument and not the argument itself). When the function exits, all local variables (other than static) are destroyed. The result of your function's assignments are never communicated back to the calling function.
Hi All, Thanks for the quick responses.
I posted a shorter example of my code. The problem turned out to be
my switch/case statement that handled key input (not posted here) and
the insertion pointer was being misshandled.
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: OMouse |
last post by:
Hi, I just switched to using STL for my linked lists and obviously I
need a way to insert. I have all the necessary includes (list &
algorithm) and the other functions that I've used (erase & find) work.
But when I try to insert the iterator that was found, gcc 3.3.4 tells
me that I'm missing a few inputs. Anyway, here's the snippet of code.
main.cpp
-----------------
#include "usernode.h"
#include <list>
|
by: Randy Bush |
last post by:
i am trying to insert into a singly linked list
hold = self.next
self.next = DaClass(value)
self.next.next = hold
but i suspect (from print statement insertions) that the result
is not as i expect. as the concept and code should be very
common, as i am too old for pride, i thought i would ask.
|
by: Tom Timmermann |
last post by:
In the process of building a link list, I noticed that successive
calls to malloc() return a pointer address that keeps getting larger.
Can I always count on this behavior and so do pointer comparisons like
< or > ? Or is it possible for malloc to return a pointer address
smaller than some previous call ?
TomT
|
by: Doug Stell |
last post by:
I am having a problem with the corruption of a list. It occurs only
the first time that I call a function and never happens on subsequent
calls. Any suggestions would be appreciated.
I call the function, passing in a list as the input data. The function
must manipulate and operate on a copy of that list's data, without
altering the list in the calling routine.
def myFunc(listA):
listB = listA
|
by: Suyash Upadhyay |
last post by:
Hello All,
I am a beginner of C Programming, I am working on linked list now-a-days, i have successfully created a linked list and displayed, but when i tried to insert an element in mid of linked list, it doesnt take place. I think I have written every thing write. Please help me,
#include "stdio.h"
struct node
{
int value;
struct node* link;
| |
by: eight02645999 |
last post by:
hi
i have a list (after reading from a file), say
data =
I wanted to insert a word after every 'a', and before every 'd'. so i
use enumerate this list:
for num,item in enumerate(data):
if "a" in item:
data.insert(num+1,"aword")
if "d" in item:
|
by: Chuckk Hubbard |
last post by:
I solved this problem. I still don't understand why, but it seems
Python was appending a reference to the first element at the end of
the list, rather than copying the data. I used something like:
"self.regionlist.append(list(self.regionlist)"
and now it works fine, i.e., altering the appended list member doesn't
change the copied one.
-Chuckk
|
by: Chuckk Hubbard |
last post by:
Hello.
This program is clunky, I know; I'm not a programmer, but I need to
use this program, so I'm writing it.
The problem:
I have a cursor following the mouse that shows frequency ratios of
potential notes in relation to 1/1 (something like Middle C). At any
time, the user may hit "t" to move 1/1 to wherever the cursor is.
There is also the option to use many regions, so that some of the
notes in the score, in region 0, for instance,...
|
by: mike_solomon |
last post by:
I have a button
<input type="submit" name="Delete" value="Delete">
This code can not be changed
I want to use Javascript to change the type
I tried:
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
| |
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: tracyyun |
last post by:
Dear forum friends,
With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
|
by: 6302768590 |
last post by:
Hai team
i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
|
by: muto222 |
last post by:
How can i add a mobile payment intergratation into php mysql website.
| |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |