Change word in a file

**thescratchy** · 03-18-2010

Hello everyone

I have a file :

Code:

<html> 
<head> 
<t i t l e>UHasselt</ t i t l e> 
</head> 
<body>
<font color = ”red”>Dit is de website van de UHasselt</font> 
<br/> 
<br/> 
<font color = ”#123456”>Info over de universiteit</font> 
<br/>
<br/> 
<a	href=”http://www. uhasselt .be”>link</a>
</body> 
</html>

And i want to change the color #123456 into the word green.

Now i know how to go threw the file and write the file.
But how can i change the word? I thought something like this :

I take the length of the word #123456, and with the function strstr() i look at the pointer of the first place. And now i am stuck.

How can i say print everything from the string until that pointer adres.
And after concatenating the word green to this string print everything else after the wordt #123456.

I really appreciate some help. I have examination tomorrow.

**thescratchy** · 03-18-2010

im sorry i forgot to mention i
i am using fgets to read data from the file, so i can work with strings

**Tool** · 03-18-2010

How can i say print everything from the string until that pointer adres.

Code:

while(p < p + number_of_chars)
    putc(*p, file);

**thescratchy** · 03-18-2010

OH my god: So simple and yet i couldnt see it

Thank you very much. I got it to work

**karthigayan** · 03-18-2010

Use this code,

Code:

#include<stdio.h>
#include <string.h>
#include<stdlib.h>
char *replace(char *str, char *from, char *to);

main()
{
        char buf[1024];
        FILE *fp;
        char *p;

        if((fp=fopen("file","r+"))==NULL)
        {
                perror("fopen:");
                exit(1);
        }
        else
        {
                while(fgets(buf,sizeof(buf),fp)!=NULL)
                {
                        printf("%s",buf);
                if((p=strstr(buf,"#123456"))!=NULL)
                {
                        printf("%s\n",replace(buf, "#123456", "green"));
                }
                }
        }

}


char *replace(char *str, char *from, char *to)
{
  static char buffer[1024];
  char *p;

  if(!(p = strstr(str, from)))
    return str;

  strncpy(buffer, str, p-str);
  buffer[p-str] = '\0';

  sprintf(buffer+(p-str), "%s%s", to, p+strlen(from));

  return buffer;
}

**thescratchy** · 03-18-2010

Thank you

**quzah** · 03-18-2010

That only replaces the word in-memory, not in-file. You cannot simply seek to a spot, find a word, and overwrite it, without rewriting the entire remainder of the file from that point on, unless the words are the exact same length (or unless the source word is longer than the target word AND you're adding in some form of padding.

Code:

#123456
green

Notice how they are not at all the same length. That means if all you do (and you're not, in the code above, you aren't doing anything to the word on disk) if seek to a spot and write out the word "green", that you'll end up with "green56" on disk. And if it were reversed, you'd be overwriting "green" with a longer word, which would mung up two extra bytes in your file.

Quzah.

**rabidbadger** · 03-18-2010

Originally Posted by karthigayan

Use this code

Erm, that code won't actually do what the OP asked for. It will output up to the line with the search string in, the line with the search string in, the same line with the string replaced, and then the rest of the file. As it's a simple fix, I don't know if you made the error for the learning benefit of the OP or not?

**Tool** · 03-18-2010

Yeah Quzah is right.

Open the wanted file for reading, then open another file for writing - you read data from the first file, write it to the second one according to readen data in the first.

After your done, you could open the first file for writing, copy all data from the 2nd file and then delete the 2nd file which you no longer need.

Thread: Change word in a file

Thread Tools

Search Thread

Display

Change word in a file

Similar Threads

Need Help Fixing My C Program. Deals with File I/O

gcc link external library

Inventory records

I'm not THAT good am I?

Encryption program