File read in problem

This is a discussion on File read in problem within the C Programming forums, part of the General Programming Boards category; Hi, I've made a function that reads in a file by first determining the file size and then reading in ...

  1. #1
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    File read in problem

    Hi,

    I've made a function that reads in a file by first determining the file size and then reading in the contents, unfortunately for some reason when the contents are read in, additional unwanted and non existent characters are being read in to (characters that aren't in the files contents), I can't see where the problem is, can anyone spot what I've done incorrectly?

    Code:
    void encrypt(char *key,char *fileIn,char *fileOut)
    {
        FILE *pFile;
        long fileSize;
        if( (pFile = fopen ( fileIn, "r")) != NULL )
        {
            fseek (pFile,0,SEEK_END);
            fileSize= ftell (pFile);
        } else {
            printf( "File could not be opened\n" );
       }
        fclose(pFile);
        char message[fileSize];
        
        if( (pFile = fopen( fileIn, "r" )) != NULL )
        {
            fread( message, sizeof( char ), (fileSize), pFile );
            printf( "Number of characters: %d\n", fileSize );
            printf( "Message reads: %s\n", message );
            fclose( pFile );
        }
       else {
            printf( "File could not be opened\n" );
       }
    }
    The function itself is incomplete I'm just trying to get the read in part of it correct first, the idea is that it will read in the contents of a plain text file into an array, alter the data and then output it to separate file (cipher file).

    at the moment when I read in a file containing the word Test, I get:

    Test (which is the contents followed by a square thing then >>-u#E and a few others I can't make on this keyboard.

    Any help is appreciated.
    Last edited by DimensionX; 11-10-2009 at 07:24 AM.

  2. #2
    Registered User rpbear's Avatar
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    this happened because you haven't init the array----message[fileSize]
    add one line after that:
    Code:
    memset(message,0,fileSize);
    second,you can't expect that the fread will read in char as much as fileSize,so you'd do this:
    Code:
    int n = fread( message, sizeof( char ), (fileSize), pFile );
            printf( "Number of characters: %d\n", n );
    don't forget add the header <memory.h>

  3. #3
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    You should allow room for one more character in the array - the terminating zero.

    I don't see why rpbear says you can not expect the number of chars requested.
    All you need to do is place a terminating nul - which would be in location...
    message[fileSize] = '\0';
    Then print it out.

  4. #4
    Registered User rpbear's Avatar
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    Thumbs up

    Quote Originally Posted by nonoob View Post
    You should allow room for one more character in the array - the terminating zero.

    I don't see why rpbear says you can not expect the number of chars requested.
    All you need to do is place a terminating nul - which would be in location...
    message[fileSize] = '\0';
    Then print it out.
    agreed!

  5. #5
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    To clarify, yes, in general you can not depend on the read returning the number of characters requested. After all, in isolation, the count is a maximum only. The file may have less. But in the context above, the count was determined via the file's size.

    There may be another complication... Does the ftell() return the raw file size? I bet it does. Depending on whether it's opened "t" or "b" mode, reads may or may not compact/expand line breaks into one/two characters. This would cause the character count to be different than expected.

  6. #6
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    Thank you both very much, it's working perfectly!

    really appreciate all the help you've both given me.

    thanks again.

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