NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/3528

Text File | 1996-08-05 | 5.8 KB | 200 lines

Newsgroups: comp.lang.c
Path: uu4news.netcom.com!zodiac!szh
From: [e-mail] (Syed Zaeem Hosain)
Subject: Re: New C Programmer Has A Problem
Message-ID: <[e-mail]>
Sender: [e-mail] (Syed Zaeem Hosain)
Nntp-Posting-Host: zodiac
Reply-To: [e-mail]
Organization: Z Consulting Group
References: <4ehpa3$[e-mail]>
Date: Mon, 29 Jan 1996 16:25:14 GMT

In article <4ehpa3$[e-mail]>, [e-mail] (Tony Syslo) writes:
>  I have a question on C... why isn't this program working?!

What are the detailed symptoms? Are they compilation or link or
run-time errors?

>  Program START:
>  /* File Open */
>
>  #include <clib/dos_protos.h>
>  #include <dos/dos.h>
>  #include <stdio.h>
>  #include <exec/types.h>

The above includes are mostly non-standard (with the exception of
stdio.h) as far as I can tell, so I am not sure if they are correct or
not.

>  void main();

This above declaration of what main returns is unnecessary and also
wrong per ANSI requirements (see later correction).

>    char *name;
>    int age;

Effectively, the above two variables have become global to the program.
In this particular case, they could be inside the main function with
similar results.

>  void main()

Instead of the above, please use (see note earlier):

   int main()

>
>  {
>    struct FileHandle *file_handle;

I do not know what the above structure is. Why not just use the FILE
pointer declaration as follows:

     FILE *file_handle;

Then you can use the more easy fopen, fclose, fread, fwrite, fprintf,
etc., functions to deal with data in the file.

>    long bytes_written;
>    long bytes_read;
>
>   printf("Enter your name: ");
>   scanf("%s",name);

This line above is one of the places where you should expect problems
(there are others in your code, but this is one of the common errors).

The comp.lang.c FAQ talks about this issue (allocating a pointer but
not initializing it to point to any valid memory before you attempt to
store data into that unassigned location).

Specifically, section 7 (Memory Allocation) in the FAQ should be read
thoroughly by you before proceeding.

>   printf("\nEnter your age: ");  scanf("%d",age);
>
>
>    file_handle=(struct FileHandle *)
>      Open("RAM:You.dat",MODE_NEWFILE);

As mentioned earlier, "fopen" is probably more easy to use. If declared
as I had mentioned earlier, the above line would become:

     file_handle = fopen("RAM:You.dat","w");

>    /* Have we opened the file successfully? */
>    if(file_handle==NULL)
>    {
>      printf("Could not open the file!\n");
>      Exit(0);

If main() is declared to be int return, then the above could be:

        return(0);

although it is more common to return 0 to imply success, so it might
be better to use:

        return(1);

or something more appropriate if you want to trap the result of the
return outside the program.

>    }
>    /* We have now opened a file, and are ready to start writing: */
>    bytes_written=Write(file_handle,name,sizeof(name));

What is the "Write" function? It is not one of the standard library
functions I am familiar with.

>    bytes_written=bytes_written+Write(file_handle,age,sizeof(age));

Some simplification (using a technique in C that is quite common) will
make the above line read as follows (even though it may be incorrect
code since I am not aware of what "Write" does):

     bytes_written += Write(file_handle,age,sizeof(age));

>
>    if(bytes_written!=sizeof(name)+sizeof(age))
>    {
>      printf("Could not save the list!\n");
>      Close(file_handle);
>      Exit(0);
>    }
>    else
>      printf("Saved successfully!\n");
>    printf("Memory cleared!\n");
>     name="";

Oops. You may have difficulty with the above ... the pointer "name" will
get set to point to another location other than allocated char array
space (after you fix the other error).

>     age=0;
>    printf("Loading!\n");
>    Seek(file_handle,0,OFFSET_BEGINNING);

Is "Seek" a valid library function?

>    bytes_read=Read(file_handle,name,sizeof(name));

The function name "Read" above is unknown to me.

>    bytes_read=bytes_read+Read(file_handle,age,sizeof(age));

Try (although see note above about the function "Read"):

     bytes_read += Read(file_handle,age,sizeof(age));

>    if(bytes_written!=sizeof(name)+sizeof(age))
>    {
>      printf("Could not read the list!\n");
>      Close(file_handle);
>      Exit(0);
>    }

Your error handling (using the number of bytes read) for determiningg
that the data was not read correctly is not a cleanly consistent method
I would recommend, although it probably will work in this case.

>    /* Print out the data: */
>      printf("Hello, %s!\",name);
                          ^
Are you missing something here?

>      printf("You are %d years old!\n",age);
>    /* Close the file: */
>    Close(file_handle);
>  }
>
>  Program END:
>
>  Any help if MUCH appreciated...
>
> I am using the SAS/C 6.50 compiler...

Well, in a number of places, your compiler should have complained about
incorrect code, or incorrect library functions (possibly - I do not
know the SAS compiler). Did this even compile and link correctly? If
so, I would recommend switching compilers <smile>. Other wise, I would
ask what symptoms you specifically experienced, and what you tried to
fix, so that we can address how you should progress next.

>  Also, is there any of you whom might have a routine to figure up random (or
>  even psuedo-random) numbers?? Some algorithm, or such, as I need one BADLY!!

Please look in the comp.lang.c FAQ for answers to the above question!

                                Z


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