appending text to existing text file

This is a discussion on appending text to existing text file within the C Programming forums, part of the General Programming Boards category; Hi team, This is doing my head in...and I'm sure i'm SO close to solving this! I need some guided ...

  1. #1
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    appending text to existing text file

    Hi team,
    This is doing my head in...and I'm sure i'm SO close to solving this! I need some guided help on how I can modify my code below, so that I can append some additional text to the beginning of a text file, which already has content within it.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
      char str[80] = "This is just some random text.\n";
      FILE *fp;
      char *p;
      int i;
    
      /* open file3.txt for output */
      if((fp = fopen("file3.txt", "w"))==NULL) {
        printf("Cannot open file.\n");
        exit(1);
      }
    
      /* write str to disk */
      p = str;
      while(*p) {
        if(fputc(*p, fp)==EOF) {
          printf("Error writing file.\n");
          exit(1);
        }
        p++;
      }
      fclose(fp);
    
      /* open file3.txt for input */
      if((fp = fopen("file3.txt", "r"))==NULL) {
        printf("Cannot open file.\n");
        exit(1);
      }
    
      /* read back the file */
      for(;;) {
         i = fgetc(fp);
         if(i == EOF) break;
         putchar(i);
      }
      fclose(fp);
    
      return 0;
    }
    Basically, what this overwrites the contents of the file and just adds "This is just some random text."...

    Would REALLY welcome any of you to show me the proper code!

    Cheers,
    K

  2. #2
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    According to http://www.cplusplus.com/reference/c...dio/fopen.html you need to use the mode "a" to append to the file.

    EDIT: U want to add to front. sorry. read the reply below me
    Last edited by 39ster; 05-28-2008 at 08:04 AM.

  3. #3
    Jack of many languages Dino's Avatar
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    To add text to the front, you have two options:

    1) Write to a new file, add the new text, and then copy all the text from the source file to the new file and when done, delete the original source file and rename the new file to the old name.

    2) Open the file for read and write, read the whole file into memory, reset the file position to zero, and then write your new data followed by all the data you read into memory.

    So, therefore, you are not so close.
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  4. #4
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    thanks guys for your quick reply!
    back to the drawing board I go.

    Todd/39ster - do you have any references to how to do the above mentioned?

    Cheers,

  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    kpax, I think it would be a very trivial task to open one file, read, then write into another file and repeat until you've finished writing the entire contents.
    Try doing that and I'm sure you can finish your code.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  6. #6
    Jack of many languages Dino's Avatar
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    Which one are you wanting to do? Have you learned about allocating memory yet?
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  7. #7
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    thanks Elysia.

    Nope haven't got to that stage about memory allocation.

    I understand exactly what I need to do - the hard parts actually coding it

  8. #8
    Jack of many languages Dino's Avatar
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    It's only hard when you let the whole scope of the effort overwhelm you.

    Divide and conquer.
    Mac and Windows cross platform programmer. Ruby lover.

    Quote of the Day
    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

  9. #9
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    Quote Originally Posted by kpax View Post
    thanks Elysia.

    Nope haven't got to that stage about memory allocation.

    I understand exactly what I need to do - the hard parts actually coding it
    And you will not learn how to do it if you don't do it yourself - just like you can't learn how to drive a car by watching someone drive on telly.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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