Re: newbie binary file I/O question

[kst@thomsoft.com (Keith Thompson)]

In <D4vHw0.LB@nvl.army.mil> shaffer@oliver (Dolores Shaffer) writes:
> I am using an old Telesoft Ada compiler on a Sun workstation.  I have
> a binary file that I would like to open and read one byte at a time.
> If the code asks the user for the file name and then stores that in
> a string variable, and the code passes that variable to the open 
> procedure, I get a NAME_ERROR and the code bombs.  If the code
> passes the name of the binary file in quotes, it works.  I am
> able to use text_io.open to open text files whose names are passed to
> open in a string variable.  Any suggestions?
[...]
> name_of_file: string(1..80);
> name_length : natural;
> 
> begin
>     text_io.put_line("enter name of file to open");
>     text_io.get_line(name_of_file,name_length);
> 
>     byte_io.open(din_file, byte_io.file_mode'first, name=>name_of_file);
> --IT BOMBS HERE!!
> --but byte_io.open(din_file, byte_io.file_mode'first, "filename"); works

The contents of the variable Name_Of_File past Name_Length are undefined.
The name the user entered is in the slice
    Name_Of_File(1 .. Name_Length)
Use that instead of just Name_Of_File in the Open call.

Someone else suggested initializing Name_Of_File to all blanks; this is
unlikely to work.  Under Unix, for example, a blank is a valid character
in a file name; "foo" and "foo " are legal and distinct file names.

Digression:
    To be more precise about what's going on, change the variable Name_Length
    to Name_Last, and use the slice
	Name_Of_File(Name_Of_File'First .. Name_Last)
    Not all strings are one-based; for strings that aren't one-based,
    the 'Last is not the same as the 'Length.  In this particular case,
    you know Name_Of_File is one-based because you declared it that way,
    but it's still better to be explicit.
end Digression;

-- 
Keith Thompson (The_Other_Keith)  kst@thomsoft.com (kst@alsys.com still works)
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