toStringz or not toStringz

[Regan Heath]

On Fri, 08 Jul 2011 18:59:47 +0100, Walter Bright  
<newshound2 at digitalmars.com> wrote:

> On 7/8/2011 4:53 AM, Regan Heath wrote:
>> On Fri, 08 Jul 2011 10:49:08 +0100, Walter Bright  
>> <newshound2 at digitalmars.com>
>> wrote:
>>
>>> On 7/8/2011 2:26 AM, Regan Heath wrote:
>>>> Why can't we have the
>>>> compiler call it automatically whenever we pass a string, or char[]  
>>>> to an extern
>>>> "C" function, where the parameter is defined as char*?
>>>
>>> Because char* in C does not necessarily mean "zero terminated string".
>>
>> Sure, but in many (most?) cases it does. And in those cases where it  
>> doesn't you
>> could argue ubyte* or byte* should have been used in the D extern "C"
>> declaration instead. Plus, in those cases, worst case scenario, D  
>> passes an
>> extra \0 byte to those functions which either ignore it because they  
>> were also
>> passed a length, or expect a fixed sized structure, or .. I don't know  
>> what as I
>> can't imagine another case where char* would be used without it being a  
>> "zero
>> terminated string", or passing/knowing the length ahead of time.
>
> In the worst case, you're adding an extra memory allocation and function  
> call overhead (that is hidden to the user, and not turn-off-able). This  
> is not acceptable when interfacing to C.

This worst case only happens when:
1. The extern "C" function takes a char* and is NOT expecting a "zero  
terminated string".
2. The char[], string, etc being passed is a fixed length array, or a  
slice which has no available space left for the \0.

So, it's rare.  I would guess a less than 1% of cases for general  
programming.

And, it *is* turn-off-able.  You simply change the extern "C" to use  
ubyte*, byte*, or void* (instead of char*).  This is arguably a better  
definition for this sort of function in the first place.

>> D is already allocating an extra \0 byte for string constants right?
>
> Yes, but in a way that is essentially free.

Yep, this is essentially free, and calling toStringz automatically would  
be almost as free, for 99% of cases.  Plus it would "just work" which is a  
big deal when you're talking about first impressions etc.

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