Re: Introductory Presentations, especially aimed at C++ programmers!

["Randy Brukardt" <randy@rrsoftware.com>]

"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:o2fagv$n4s$1@dont-email.me...
> On 12/09/2016 03:01 PM, Randy Brukardt wrote:
>> "Paul Rubin" <no.email@nospam.invalid> wrote in message
>> news:877f7b5llo.fsf@nightsong.com...
>>>> exponentially better than being prevented from overflowing a buffer is
>>>> being able to figure out how to do
>>>> declare
>>>>    B : Buffer (1 .. Just_The_Right_Size);
>>>
>>> Alternatively the buffer could be dynamically sized according to the
>>> data.  That's not in the Ada spirit because of the possible OOM and
>>> memory allocation latency getting in the way of embedded realtime
>>> applications, but for a workstation app it's perfectly workable.
>>> Horses for courses.
>>
>> That's one possible way to use the API in question, since there's no way 
>> to
>> find out beforehand how much data you'll need. (You could ask for the 
>> size
>> ahead of time, but of course that's a potential race condition so it 
>> doesn't
>> really help.)
>
> I was including in being able to do
>
> declare
>    B : Buffer (1 .. Just_The_Right_Size);
>
> such things as
>
> declare
>    S : String := Get_Line;
>
> and there's usually a way to do that even when you don't know beforehand 
> how big the result will be. After all, the Get_Line function doesn't know 
> beforehand how long a String it will return. I don't how the API in 
> question works, so I can't say for sure if there's a way to do this for 
> it, but there usually is.

For reading from a device (like a keyboard), it's impossible to know ahead 
of time what is going to be read (without forcing some sort of pause into 
the program which is usually not wanted). A Get_Line like the above 
generally requires some sort of incremental allocation (a buffer is 
allocated, if its not big enough a bigger one is allocated, the first one is 
copied into it, and then we repeat until a <LF> appears), and thus you need 
to avoid such Get_Lines for things where performance might matter (like 
reading from a file). [If you can figure out what kind of entity a handle 
accesses, then perhaps you could use a different implementation for a file 
vs. a device; as always, how complicated do you want to make your I/O 
libraries??]

                                     Randy.