toStringz or not toStringz

[Regan Heath]

On Tue, 12 Jul 2011 15:18:04 +0100, Steven Schveighoffer  
<schveiguy at yahoo.com> wrote:

> On Tue, 12 Jul 2011 09:54:15 -0400, Regan Heath <regan at netmail.co.nz>  
> wrote:
>
>> 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.
>
> What if you expect the function is expecting to write to the buffer, and  
> the compiler just made a copy of it?  Won't that be pretty surprising?

Assuming a C function in this form:

   void write_to_buffer(char *buffer, int length);

You might initially extern it as:

   extern "C" void write_to_buffer(char *buffer, int length);

And, you could call it one of 2 ways (legitimately):

   char[] foo = new char[100];
   write_to_buffer(foo, foo.length);

or:

   char[100] foo;
   write_to_buffer(foo, foo.length);

and in both cases, toStringz would do nothing as foo is zero terminated  
already (in both cases), or am I wrong about that?

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