Inserting text into a file

This is a discussion on Inserting text into a file within the C Programming forums, part of the General Programming Boards category; Hi all, I'm having difficulties inserting a string into a text file. Here's my code: Code: int main() { FILE ...

  1. #1
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    Inserting text into a file

    Hi all,

    I'm having difficulties inserting a string into a text file. Here's my code:

    Code:
    int main() {
    
    	FILE *f;
    	char c=0;
    	int br=0;
    
    	if ((f=fopen("fajl.htm", "r+"))==NULL) {
    		exit(1);
    	}
    
    	while ((c=fgetc(f))!=EOF) {
    
    		if (c=='&') {
    				fputs("blah", f);
    				printf("Job done.\n");
    		}
    	}
    
    	fclose(f);
    
    	return 0;
    
    }
    What I am trying to do is insert a string after a certain character. This code does not work for some reason, when it goes through the file and finds this specific character, it will not insert my string, but continue to the next character.

    What am I doing wrong?

  2. #2
    former member Brain Cell's Avatar
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    you're trying to write to the file right? fix the mode then..

    besides , the while loop would execute anyway regardless if the file was successfuly opened or not.
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  3. #3
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    Quote Originally Posted by Brain Cell
    you're trying to write to the file right? fix the mode then..
    If I use the w mode, it will delete the contents of the file before writing.

  4. #4
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    You can use the a mode to append.

  5. #5
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    Guys, "r+" is the correct mode for him. "a" would stick him at the end of the file. He wants to insert after a certain character in the file. And how would the while() loop execute if the file is incorrectly opened if exit() is being called in that situation?

    It would be helpful to see the contents of the file.

    NOTE: You can't "insert" text in a file. You'll overwrite what's already there. You can read in the rest of the file after that point to a buffer, write your new text, and then dump the buffer back onto the end of the file though.
    Last edited by itsme86; 11-05-2004 at 01:43 PM.
    If you understand what you're doing, you're not learning anything.

  6. #6
    Just Lurking Dave_Sinkula's Avatar
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    7. It is easier to write an incorrect program than understand a correct one.
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  7. #7
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    Quote Originally Posted by itsme86
    NOTE: You can't "insert" text in a file. You'll overwrite what's already there. You can read in the rest of the file after that point to a buffer, write your new text, and then dump the buffer back onto the end of the file though.
    What I'm actually trying to do is replace ampersands (&) in a HTML file with &. So when the ampersand is found, the program would insert amp; after it.

    What you're suggesting is to define a large character array where I'd put what remains in the file after the specific character? How large should the array be, considering that the HTML files vary from 5 to 80 KB?

  8. #8
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    That's one option. Another option would be to use a separate output file. You could read each character in the file like you are now. Write the character to the output file and then check if it was an ampersand. If it was, also write "amp" to the output file.

    To find out the size of the file (in case you go with the first option) you can use stat() on the file. The st_size member is the size of the file. Then you can malloc() that many bytes for the buffer.
    If you understand what you're doing, you're not learning anything.

  9. #9
    ATH0 quzah's Avatar
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    Code:
    while( (c = fgetc( infile )) != EOF )
    {
        if( c == '&' )
        {
            fprintf( outfile, "&" );
        }
        else
        {
            fputc( c, outfile );
        }
    }
    You did say "every &".

    Quzah.
    Hope is the first step on the road to disappointment.

  10. #10
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    Quote Originally Posted by itsme86
    That's one option. Another option would be to use a separate output file. You could read each character in the file like you are now. Write the character to the output file and then check if it was an ampersand. If it was, also write "amp" to the output file.

    To find out the size of the file (in case you go with the first option) you can use stat() on the file. The st_size member is the size of the file. Then you can malloc() that many bytes for the buffer.
    Thanks, you've been much helpful!!

  11. #11
    former member Brain Cell's Avatar
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    Guys, "r+" is the correct mode for him. "a" would stick him at the end of the file.
    aw i didn't notice the plus nor that you actually want to write AND read from the file.

    sorry Ariod..
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  12. #12
    Registered User caroundw5h's Avatar
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    Quote Originally Posted by itsme86
    That's one option. Another option would be to use a separate output file. You could read each character in the file like you are now. Write the character to the output file and then check if it was an ampersand. If it was, also write "amp" to the output file.

    To find out the size of the file (in case you go with the first option) you can use stat() on the file. The st_size member is the size of the file. Then you can malloc() that many bytes for the buffer.
    The idea is a good one, however this is assuming the op is on unix or unix variant.

  13. #13
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    Quote Originally Posted by caroundw5h
    The idea is a good one, however this is assuming the op is on unix or unix variant.
    True enough. I failed to mention that. Thanks.
    If you understand what you're doing, you're not learning anything.

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