Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

First chance exception and string concatenation: two related questions

Posted on 2004-04-10
8
Medium Priority
?
794 Views
Last Modified: 2010-04-15
Hello.

Please look at the following code, intended to read 10 chars from a file and then append it to a char array.  The end result is that the multiple calls to fgets should be represented as array y:

char y[30];
memset(y, ' ', 30);

FILE* ifp = fopen("input.txt", "r");

char sz[10];

while (strlen(y) != 30 && (!feof(ifp)) ) {
      fgets(sz, 10, ifp);
      strcat(y, sz);
}

fputs(y, stdout);

The input file is

line 1
line 2
line 3
line 4
line 5
line 6

and the output I get is

                              @line 1
line 2
line 3
line 4
line 5
line 6
line 6

So,

1) Why do I have the rubbish at the start of line 1 of the output ?
2) I get a first chance exception when run in debug mode *when the input file has one blank line at the end*.  This does not happen in release mode, and does not happen at all without the final blank line.  The code crashes at

if ( wchar > 255 )  /* validate high byte */

(XWCTOMB.c, line 116).

Any ideas ?  I know that in general first chance exceptions can be ignored, but just wondered why this is happening.

(25 points per question here)

TIA !
0
Comment
Question by:mrwad99
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 3
8 Comments
 
LVL 46

Accepted Solution

by:
Kent Olsen earned 120 total points
ID: 10797139
Hi mrwad99,

1a)  You initialize y[] with spaces.  You should initilize the first charter to 0 ('\0').
1b)  Define y[] as y[40] and test for strlen(y) <= 30.  You're reading 6 characters (plus end-of-string, plus possibly carriage-return) into a 10 character array.  You might not fill the array exactly full.  Plus, even if you do put exactly 30 characters into the array, you're writing 31-characters to terminate the string and overflowing the array.

2)  The program is using ASCII characters.  Why are you testing for wide characters?


Good Luck!
Kent
0
 
LVL 19

Author Comment

by:mrwad99
ID: 10797202
1) Right thanks Kent, it was the issue with initialising y to hold ' ' not '\0' that was causing the problem.
2) I am not testing for any type of character; the code I posted in the original question is all the code I have (less main() and a few #includes).  The line the code crashes on is in XWCTOMB.c, line 116: I found this out by running the debugger.  Anyway that is redundant now because with the new changes that does not happen.

So what I think y will look like is:

line 1\0line 2\0line 3\0line 4\0line5\0line 6\0

Or would it look like

line 1line2line 3line 4line 5line 6\0

After reading all the file in (with an appropriately sized char[])

TIA !
0
 
LVL 9

Assisted Solution

by:ankuratvb
ankuratvb earned 80 total points
ID: 10797219
The output would be:

line 1line2line 3line 4line 5line 6\0
0
VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

 
LVL 19

Author Comment

by:mrwad99
ID: 10797226
And I take it that is because when using strcat(), the first character of the string to be concatenated is placed over any preceeding '\0' ??
0
 
LVL 9

Expert Comment

by:ankuratvb
ID: 10797251
Yes.
And '\0' is placed at the end of the concatenated string.
0
 
LVL 19

Author Comment

by:mrwad99
ID: 10797265
Points split in favour of Kdo since he answered the primary questions; ankuratvb you get 20 of the 50 since you sorted my last query.

Thanks a lot both !
0
 
LVL 9

Expert Comment

by:ankuratvb
ID: 10797269
BTW,strcat() searches for the first '\0' and concatenates the second string from here.

Try this:

#include <string.h>
#include <stdio.h>

int main(void)
{
   char destination[25]="a\0b";
   char *blank = " ", *c = "C++", *turbo = "Turbo";

   strcat(destination, turbo);

   printf("%s\n", destination);
   return 0;
}

The result is "aTurbo".
0
 
LVL 19

Author Comment

by:mrwad99
ID: 10797284
Yep; thanks for solidifying that ankuratvb !  Greatly appreciated.
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
Preface I don't like visual development tools that are supposed to write a program for me. Even if it is Xcode and I can use Interface Builder. Yes, it is a perfect tool and has helped me a lot, mainly, in the beginning, when my programs were small…
The goal of this video is to provide viewers with basic examples to understand how to use strings and some functions related to them in the C programming language.
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use nested-loops in the C programming language.

715 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question