W+ file blues.

This is a discussion on W+ file blues. within the C Programming forums, part of the General Programming Boards category; Code: FILE *superFile = fopen("test.txt","w+"); Erases the contents of the file test.txt. Isn't this supposed to open the file, leaving ...

  1. #1
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    Unhappy W+ file blues.

    Code:
    FILE *superFile = fopen("test.txt","w+");
    Erases the contents of the file test.txt. Isn't this supposed to open the file, leaving it intact and still allowing you to read and write? If not, is there another way?

  2. #2
    and the hat of wrongness Salem's Avatar
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    > leaving it intact and still allowing you to read and write?
    No, that's what "a+" does

  3. #3
    Skunkmeister Stoned_Coder's Avatar
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    FILE *superFile = fopen("test.txt","a");

    I think
    Free the weed!! Class B to class C is not good enough!!
    And the FAQ is here :- http://faq.cprogramming.com/cgi-bin/smartfaq.cgi

  4. #4
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    Thought a wrote to the end of the file.
    I'll try a+.

  5. #5
    and the hat of wrongness Salem's Avatar
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    > Thought a wrote to the end of the file.
    It does (initially), if you want to write elsewhere, then you'll need to fseek to it first

  6. #6
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    it's not seeking to the beginning.

    Code:
    FILE *fp = fopen("a.txt","a+");
    fseek(fp,0,SEEK_SET);
    fputc('x',fp);
    fclose(fp);
    It still adds to the end

  7. #7
    and the hat of wrongness Salem's Avatar
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    Odd, it works here - gcc version 3.0.3(DJGPP)

    Code:
    #include <stdio.h> 
    
    int main ( ) {
      FILE *fp = fopen( "test.txt", "a+" );
      int ch;
    
      fseek( fp, 0, SEEK_SET );
      ch = fgetc(fp);
      printf( "Ch read=%c\n", ch );
    
      fseek( fp, 0, SEEK_SET );
      fputc('@',fp);
      printf( "Wrote @\n" );
    
      fseek( fp, 0, SEEK_SET );
      ch = fgetc(fp);
      printf( "Ch read=%c\n", ch );
    
      fclose( fp );
    
      return 0;
    }
    > a.exe
    Ch read=H
    Wrote @
    Ch read=@

  8. #8
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    Huh. Dev-c++ sucks .

    Maybe windows.h is ****ing it up?

  9. #9
    B26354 Deckard's Avatar
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    r - Open text file for reading. The stream is positioned at the beginning of the file.

    r+ - Open for reading and writing. The stream is positioned at the beginning of the file.

    w - Truncate file to zero length or create text file for writing. The stream is positioned at the beginning of the file.

    w+ - Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file.

    a - Open for writing. The file is created if it does not exist. The stream is positioned at the end of the file.

    a+ - Open for reading and writing. The file is created if it does not exist. The stream is positioned at the end of the file.

    (From the fopen() man page)
    Jason Deckard

  10. #10
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    >r+ - Open for reading and writing. The stream is positioned at the beginning of the file.

    This one sounds like it would do the trick.

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