reading and writing to a file

This is a discussion on reading and writing to a file within the C Programming forums, part of the General Programming Boards category; I gotta be close on this. The new file is not created and I can't figure it out. Here's what ...

  1. #1
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    reading and writing to a file

    I gotta be close on this. The new file is not created and I can't figure it out.

    Here's what I have.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define MaxNameLen 255
    #define MaxLineLen 255
    
    int main(int argc, char** argv)
    {
        char fileName[MaxNameLen + 1];
        char copyName[MaxNameLen + 1];
        FILE *myfile;
        FILE *newfile;
    
        printf( "Enter the name of a file to copy from: " );
        fgets( fileName, sizeof( fileName ), stdin );
    
        if( fileName[strlen( fileName ) - 1] == '\n' )
        {
            fileName[strlen( fileName ) - 1] = '\0';
        }
    
        myfile = fopen(fileName, "r");
        if (myfile == NULL)
        {
            printf("Cannot open &#37;s\n", fileName);
            return(1);
        }
    
        fscanf(myfile, "%s", &fileName);
    
        printf( "Enter the name of a file to copy   to: ");
        fgets( copyName, sizeof( fileName ), stdin );
        
         if( copyName[strlen( copyName ) - 1] == '\n' )
        {
            copyName[strlen( copyName ) - 1] = '\0';
        }
    
        newfile = fopen(copyName, "w");
        fprintf( newfile, "%s", myfile);
    
        fclose(myfile);
        fclose(newfile);
        return (0);
    }
    I wonder if I am actually copying anything.

    Any insight?
    Thanks
    Last edited by tikelele; 11-26-2007 at 08:14 PM.

  2. #2
    Jack of many languages Dino's Avatar
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    Why don't you apply the same "newline removal" code to the output file name and see what happens.

    Todd

  3. #3
    Deathray Engineer MacGyver's Avatar
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    Code:
    fscanf(myfile, "&#37;s", &fileName);
    What is the purpose of this?

    Code:
    fgets( copyName, sizeof( fileName ), stdin );
    Although no issue because they are the same size, this is a bad practice. The second arg should be sizeof( copyName ).

    Also, you should check if newfile is NULL or not.

    Code:
    fprintf( newfile, "%s", myfile);
    This is pure garbage. You're writing a FILE * as if it's a char *. You're going to have issues. You have to actually fgets() or fgetc() the info from the first file and then fprintf(), or fputc() it all into the new file.

  4. #4
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    great thank you. I did exactly that and the output file was created.

    It had JUNK in it, but I guess that's what the programmer (me) made it do.

    I know I am either not fscanf or fprintf correctly.

  5. #5
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    i changed thing but I am getting a file that goes on forever.
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define MaxNameLen 255
    #define MaxLineLen 255
    
    int main(int argc, char** argv)
    {
        
        char fileName[MaxNameLen + 1];
        char copyName[MaxNameLen + 1];
        FILE *myfile;
        FILE *newfile;
        
    
        printf( "Enter the name of a file to copy from: " );
        fgets( fileName, sizeof( fileName ), stdin );
    
        if( fileName[strlen( fileName ) - 1] == '\n' )
        {
            fileName[strlen( fileName ) - 1] = '\0';
        }
    
        myfile = fopen(fileName, "r");
        if (myfile == NULL)
        {
            printf("Cannot open &#37;s\n", fileName);
            return(1);
        }
        printf( "Enter the name of a file to copy   to: ");
        fgets( copyName, sizeof( copyName ), stdin );
    
        if( copyName[strlen( copyName ) - 1] == '\n' )
        {
            copyName[strlen( copyName ) - 1] = '\0';
        }
    
        newfile = fopen(copyName, "w");
        if (newfile == NULL)
        {
            printf("Cannot create %s\n", copyName);
            return(1);
        }
    
        while (1)
        {
            fgets (fileName , sizeof( fileName ), myfile);
            if (fileName == EOF)
            {
                break;
            }
            else
            {
                fprintf( newfile, "%s", fileName);
            }
        }
    
        fclose(myfile);
        fclose(newfile);
        return (0);
    }
    Last edited by tikelele; 11-26-2007 at 09:17 PM.

  6. #6
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    i beleive i have it.

    Code:
    while (!feof(myfile))
        {
            fgets (fileName , sizeof( fileName ), myfile);
            fprintf( newfile, "%s", fileName);        
        }
    thanks everyone

  7. #7
    Deathray Engineer MacGyver's Avatar
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    That's an incorrect way to do it. Don't use feof() to control a loop. Use fgets() as your loop condition.

  8. #8
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    i did but i cant get it to stop at the end of the file

  9. #9
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by tikelele View Post
    i did but i cant get it to stop at the end of the file
    The following doesn't work?

    Code:
    while (fgets (fileName , sizeof( fileName ), myfile))
        {
            fprintf( newfile, "%s", fileName);        
        }

  10. #10
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    yes it does. at first it didn't because i had a typo

    Thanks all!

  11. #11
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    @MacGyver (or anyone else who knows)

    I wanted to know what the consequesces of using feof() as the loop control. I changed it to the proper fgets() but I am curious because feof() worked. I am guessing that when it works great...but when it doesn't then its real bad.

    I am just wondering what kind of dynamite I was toying with
    Thanks for any reply

  12. #12
    Deathray Engineer MacGyver's Avatar
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  13. #13
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    FAQs
    shudda known!

    Thank you
    MacGyver

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