943,879 Members | Top Members by Rank

Ad:
  • C++ Discussion Thread
  • Unsolved
  • Views: 7592
  • C++ RSS
Feb 18th, 2007
0

Scanning a text file for a string

Expand Post »
ok so im scanning this text file for the string "model=" the problem is, i need to pull the numbers after that string until it reached the end of that line, this is an easy script but for some reason its just not happening. If someone smarter than myself could tell me where the script went wrong that would be awesome. Please don't send me a script completely different, I need it in this format to work with my project. Thanks!

Here is my code
#include <fstream>
#include <iostream>
 
using namespace std;
int main()
{
 ifstream openfile;                    
//input file
 openfile.open("modelset.txt");  
//input file
 
 char bigarray[300];
//array that takes value of the whole line being scanned
 char thearray[300];
//array that takes value of big array until =="model=" or '\n'
 char str;
//character (used in thearray to go through each value of bigarray
 
 ofstream File;                     
//output file (is created)
    File.open("testmodel.txt"); 
//output file (is created)
 
    while(!openfile.eof()) 
//while input isnt at the end of the file
    {                                           
        openfile.getline(bigarray,300); 
//set the current line values to bigarray
        int i=0;
//used to go through thearray one spot at a time
 
        while (str !='\n' && thearray!="model=") 
//set all values of thearray to bigarray until its end of line or "model="
        {
              thearray[i] = bigarray[i];                   
              i++;
        }
 
        i=0;    
//set i back to 0 so thearray starts at thearray[0]
 
        if (thearray=="model=")  
//see if its =="model="
        {
           delete [] thearray; 
//clear all values of thearray (is this right?)
           int testarray=1;
//boolean used so I don't effect the value of thearray
 
           while ( testarray==1 ) 
//while my boolean is true (redundant but important)
           {
                 openfile.get(str);
//start scanning thearray again (this starts after model=)
                 thearray[i] = str;  
                 i++;
                 if (str=='\n'); 
//set my boolean false if its end of line
                 {
                    testarray = 0;
                 }
           }
 
        File << thearray << "\n"; 
//print thearray (the numbers after "model=") into my output file "File" (testmodel.txt)
        }   
 }
}

Yes i know, terrible commenting but i couldnt cmment to the right of ecah line, you get the idea. The comments are under the line that they refer to.

I've attached modelset.txt if you want to see (no i cant edit this file)
The actual modelset.txt is 5.3meg so i just sent this as an example
Attached Files
File Type: txt modelset.txt (412 Bytes, 58 views)
Last edited by dalton; Feb 18th, 2007 at 2:42 pm.
Similar Threads
Reputation Points: 10
Solved Threads: 0
Newbie Poster
dalton is offline Offline
2 posts
since Feb 2007
Feb 18th, 2007
0

Re: Scanning a text file for a string

I think ye' problems start here:

while (str !='\n' && thearray!="model=") 
//set all values of thearray to bigarray until its end of line or "model="
        {
              thearray[i] = bigarray[i];                   
              i++;
        }

If you were using <string> class objects, you would able to make the != comparison. However, the only way you could make a boolean comparison between a cstring thearray and a string literal "model=" would be to:

1. First, make sure that in your text file, "model=" is followed immediately by a null terminating character '\0' (using escape characters in your .txt file works best when your file is opened in binary mode)

2. Using the <cstring> function strcmp( ), you can make a direct comparison between two character arrays. The function will return 0 if there are no differences between the cstrings.

Example, lets say you called openfile.getline(bigarray,300); Assuming that the first line of the .txt file contains the "model=" string token you are looking for, bigarray would then look like this:
C++ Syntax (Toggle Plain Text)
  1. [m][o][d][e][l][=][\0][4][9][5][2]
Notice that the delimiting '\n' newline character has been discarded by use of the getline( ) function. Tip: you will probably want the '\n' newline character in this case in order to determine the end of your array. Either add back in the '\n' character yourself, or use get( ) instead of getline( ).

With the null-terminated "model=", we can now pass bigarray into the strcmp( ) function, and it will only access the cstring up until it hits a null termiator. Even though bigarray has a whole bunch of stuff in it, strcmp(bigarray, "model=") would still return 0 indicating that the cstrings are equal.

At this point, you have determined that the line you extracted from your text file is what you are looking for. You can now make the assumption that everything starting at bigarray[7] will contain the numbers.
Last edited by Ancient Dragon; Feb 18th, 2007 at 5:13 pm. Reason: changed last paragraph per poster's request
Reputation Points: 237
Solved Threads: 117
Practically a Posting Shark
Clinton Portis is offline Offline
822 posts
since Oct 2005
Feb 18th, 2007
0

Re: Scanning a text file for a string

Since you are using C++ already, why not do something simple like:
C++ Syntax (Toggle Plain Text)
  1. // Not tested
  2. #include <fstream>
  3. #include <string>
  4.  
  5. int main ()
  6. {
  7. using namespace std ;
  8.  
  9. string my_str ;
  10. const char search[] = "model=" ;
  11. size_t size = strlen (search) ;
  12. size_t pos = 0 ;
  13.  
  14. ifstream in ("modelset.txt") ;
  15. ofstream out ("output.txt") ;
  16.  
  17. while ( getline(in, my_str).good () )
  18. {
  19. if ( (pos = my_str.find (search, 0)) != string::npos )
  20. {
  21. my_str = my_str.erase (pos, size) ;
  22. out << atoi (my_str.c_str()) << '\n';
  23. }
  24. }
  25.  
  26. // close the file streams
  27. in.close () ;
  28. out.close () ;
  29.  
  30. getchar ( ) ;
  31. return 0 ;
  32. }

Modify this basic framework to suit your needs.

Oh and btw, don't PM people, its rude. If we get time, we will definately help you out.
Last edited by ~s.o.s~; Feb 18th, 2007 at 4:12 pm.
Super Moderator
Featured Poster
Reputation Points: 3233
Solved Threads: 719
Failure as a human
~s.o.s~ is offline Offline
8,871 posts
since Jun 2006
Feb 18th, 2007
0

Re: Scanning a text file for a string

>Since you are using C++ already, why not do something simple like:

Prolly because his school wants him/her to use and get to know char[] arrays.


>out << atoi (my_str.c_str()) << '\n';

Don't use atoi with c++ or even c for that matter. It is best avoided. Use stringstream instead.

http://www.daniweb.com/techtalkforums/thread39691.html

Oh and I just noticed an EOF in the OPs code which in most circumstances is best avoided.
Last edited by iamthwee; Feb 18th, 2007 at 4:34 pm.
Featured Poster
Reputation Points: 1536
Solved Threads: 431
Posting Expert
iamthwee is offline Offline
5,865 posts
since Aug 2005
Feb 18th, 2007
0

Re: Scanning a text file for a string

Click to Expand / Collapse  Quote originally posted by iamthwee ...
>out << atoi (my_str.c_str()) << '\n';

Don't use atoi with c++ or even c for that matter. It is best avoided. Use stringstream instead.
I just gave him a dummy and trivial working solution. If I would have used string streams it would have as well completed his project.

And btw atoi is not always bad, depends on the context which it is used. See this snippet.
Last edited by ~s.o.s~; Feb 18th, 2007 at 10:20 pm.
Super Moderator
Featured Poster
Reputation Points: 3233
Solved Threads: 719
Failure as a human
~s.o.s~ is offline Offline
8,871 posts
since Jun 2006
Feb 18th, 2007
0

Re: Scanning a text file for a string

Click to Expand / Collapse  Quote originally posted by ~s.o.s~ ...
And btw atoi is not always bad, depends on the context which it is used. See this snippet.
I followed your link because now I'm intrigued about atoi, however is for C++ and I don't know anything about it. Do you have another link that shows why is bad to use that function in C. I have used it several times, in the past, following books examples.
Aia
Reputation Points: 2224
Solved Threads: 218
Nearly a Posting Maven
Aia is offline Offline
2,304 posts
since Dec 2006
Feb 18th, 2007
0

Re: Scanning a text file for a string

Click to Expand / Collapse  Quote originally posted by Aia ...
I followed your link because now I'm intrigued about atoi, however is for C++ and I don't know anything about it. Do you have another link that shows why is bad to use that function in C. I have used it several times, in the past, following books examples.
See this excellent post by Narue:
http://www.daniweb.com/techtalkforum...tml#post191438

Another way in C for conversion is to validate the string with strcspn and then use sscanf to retrieve it (although that would be kind of pointless; better to use strtol).
Team Colleague
Reputation Points: 2240
Solved Threads: 338
Vampirical Lurker
John A is offline Offline
5,055 posts
since Apr 2006
Feb 19th, 2007
0

Re: Scanning a text file for a string

Click to Expand / Collapse  Quote originally posted by Aia ...
I followed your link because now I'm intrigued about atoi, however is for C++ and I don't know anything about it. Do you have another link that shows why is bad to use that function in C. I have used it several times, in the past, following books examples.
The way in which I used atoi in that snippet was relatively safe since the string is only to passed to atoi if it contains only digits and nothing else (I make this sure in the if condition). So the chances of junk gettting to passed to atoi are none and hence it functions properly in the given context.

I could have used stringstreams but would have been an overkill considering that I know before hand the kind of input which would be passed to the atoi. An important part of being a programmer is the proper selection of tools suiting the situation under consideration.
Last edited by ~s.o.s~; Feb 19th, 2007 at 11:39 am.
Super Moderator
Featured Poster
Reputation Points: 3233
Solved Threads: 719
Failure as a human
~s.o.s~ is offline Offline
8,871 posts
since Jun 2006
Feb 19th, 2007
1

Re: Scanning a text file for a string

Click to Expand / Collapse  Quote originally posted by Aia ...
I followed your link because now I'm intrigued about atoi, however is for C++ and I don't know anything about it. Do you have another link that shows why is bad to use that function in C. I have used it several times, in the past, following books examples.
Read that link I provided to show you why atoi() is bad. There are much better options to choose from in c as briefly mentioned by joeprogrammer.
Featured Poster
Reputation Points: 1536
Solved Threads: 431
Posting Expert
iamthwee is offline Offline
5,865 posts
since Aug 2005

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.
Message:
Previous Thread in C++ Forum Timeline: Time check problem
Next Thread in C++ Forum Timeline: Overloading << & >> operators





About Us | Contact Us | Advertise | Acceptable Use Policy
Forum Index | Build Custom RSS Feed


Follow us on Twitter


© 2011 DaniWeb® LLC