reading from text file

This is a discussion on reading from text file within the C Programming forums, part of the General Programming Boards category; i know this has to be simple, but ive been reading the tutorials, and searched through about 15 pages of ...

  1. #1
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    reading from text file

    i know this has to be simple, but ive been reading the tutorials, and searched through about 15 pages of threads looking for my problem to no avail .

    the .txt file is nothing more than "123456789". i was hoping to read one character at a time and eventually put each in an array[10], but i thought i would just try to print it out on screen first. i don't get a console window at all.


    Code:
    #include <stdio.h>
    
    int main()
    {
    
       FILE *otn = fopen ("c:\\onethroughnine.txt", "r");
       unsigned char x;
       while  ( ( x = fgetc( otn ) ) != EOF ) {
              printf( "%c", x );
       }
       fclose ( otn );
       getchar();
    }


    the compiler reports no errors, but this output:

    p:\c projects\untitled1.c: In function `main':
    p:\c projects\untitled1.c:8: warning: comparison is always true due to limited range of data type

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    Code:
    unsigned char x;
    ->
    Code:
    int x;
    EOF is an int value.
    dwk

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  3. #3
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    change unsigned char x, to just char x.
    -"What we wish, we readily believe, and what we ourselves think, we imagine others think also."
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  4. #4
    Frequently Quite Prolix dwks's Avatar
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    No, char x would be worse. int x is what you want. See the FAQ.
    Last edited by dwks; 11-04-2005 at 03:37 PM.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


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  5. #5
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    perfect!


    maybe you could help me understand from the tutorial example why unsigned char is used:

    Code:
    #include <stdio.h>
    
    int main ( int argc, char *argv[] )
    {
        if ( argc != 2 ) /* argc should be 2 for correct execution */
        {
            /* We print argv[0] assuming it is the program name */
            printf( "usage: %s filename", argv[0] );
        }
        else 
        {
            // We assume argv[1] is a filename to open
            FILE *file = fopen( argv[1], "r" );
    
            /* fopen returns 0, the NULL pointer, on failure */
            if ( file == 0 )
            {
                printf( "Could not open file\n" );
            }
            else 
            {
                unsigned char x;
                /* read one character at a time from file, stopping at EOF, which
                   indicates the end of the file.  Note that the idiom of "assign
                   to a variable, check the value" used below works because
                   the assignment statement evaluates to the value assigned. */
                while  ( ( x = fgetc( file ) ) != EOF )
                {
                    printf( "%c", x );
                }
            }
            fclose( file );
        }
    }

    thanks for the help

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    That is definitely wrong. See the FAQ link I provided.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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  7. #7
    Bioport Productions
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    They're right, one thing you could do is typecast fgetc to return a char instead of an int. EOF is -1 so you will need a signed char to do it.
    -"What we wish, we readily believe, and what we ourselves think, we imagine others think also."
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  8. #8
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    thanks alot for your help. up and running.

  9. #9
    Frequently Quite Prolix dwks's Avatar
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    They're right, one thing you could do is typecast fgetc to return a char instead of an int. EOF is -1 so you will need a signed char to do it.
    Did you read the FAQ?

    Yes, you could typecast it, but what if the file contains the character (-1, I mean)?
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


    Other boards: DaniWeb, TPS
    Unofficial Wiki FAQ: cpwiki.sf.net

    My website: http://dwks.theprogrammingsite.com/
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