Thread: File handling

Hi i want to create a program that examines the content of a file just a text file.
My problem is i want to search for a pattern and remove then in my file for example the content of a file is:
the@4
!3the
th-7e
th&^9e

i want to create a code that will recognize a "pattern" in that example the pattern is symbol followed by a number if the program recognizes that pattern it will remove the symbol and the number so the output will become :
the
the
the
the

is it possible?? cause my problem is when it recognizes that pattern it should take 2 stepbackward so that i could delete them in the file then after i delete that how could i concatenate the result string...for example th&7e
the output after the deleted characters th e how could i concatenate them so that the output will become the? thanks

First, I should say that they use patterns with regular expression functions, which I know next to nothing about, but you should google or search the forum, for, and see what's up with that.

To "roll your own", you would want to:

create a char buffer
read in text from the file, into this buffer
use strchr(), strstr() or another string searching function to locate the pattern you want, in the buffer
make your changes to the text in the buffer
write out the buffer contents to a new file
when finished, close all files, delete the old file, and rename the new file, to the old filename

If you try to read, then reposition the file pointer, then write some other data, then shift all the data behind it forward, because you deleted some char's, then repeat it numerous times - you're very likely to damage the file.

Make sense?

Try this code,

Code:

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

#include        <ctype.h>
#define MAXLINE 100
main()
{
        FILE *fp;
        FILE *new;
        char buf[100];
        char buf1[100];
        int i;
        int j;

        if((new=fopen("new_file","w+"))==NULL)
                perror("File open error");

        if((fp=fopen("file","r+"))==NULL)
                perror("File open error");
        else
        {
                while (fgets(buf, MAXLINE, fp) != NULL) {
                        j=0;
                        for(i=0; i<=strlen(buf); i++)
                        {
                                if(!isalpha(buf[i]))
                                        ;
                                else
                                        buf1[j++]=buf[i];
                        }
                        buf1[j]='\n';
                        buf1[j+1]='\0';
                        fputs(buf1,new);

                }

        }
        fclose(fp);
        fclose(new);
        system("mv new_file file");
        exit;
}

If you know how-to, you can extract substrings from the textfile using the regcomp() and regexec() functions.