In article <468s1qF9ru5hU1@individual.net>,
 Dietmar Kuehl <dietmar_kuehl@yahoo.com> wrote:

> JustSomeGuy wrote:
> > This is what I've written but I'm not sure if I've garanteed to have
> > the c_str() method return a buffer that is null padded.
>
> The method 'c_str()' will return a pointer to a null-terminated
> representation of the 'std::string's content. That is, you will
> have an extra null-character tagged on to the 'std::string's
> content. If the 'std::string's content contains null-characters,
> you cannot process the result of 'c_str()' with the 'str...()'
> functions because these might stop at the first embedded
> null-character. Thus, you probably should use the 'data()' method
> instead because this has the same effect as 'c_str()' except that
> it does not add an extra null-character.

Let's say I have a string class that doesn't hold its data in a
contiguous array but still wants to conform to the standard. This would
mean I have to create an array and fill it whenever c_str is called (and
I'm free to delete it whenever a non-const member-function is called.)

Would my class be standard conforming if I only made a c_str array up to
the first null? (I expect that data would have to have all the
characters.)

In other words given:

int main()
{
   std::string s = "Hello! World";
   s[6] = 0;
   const char* foo = s.c_str();
   char bar[6];
   std::strcpy( bar, foo + 7 );
   std::cout << bar;
}

Does the standard define the output of the above program?


--
Magic depends on tradition and belief. It does not welcome observation,
nor does it profit by experiment. On the other hand, science is based
on experience; it is open to correction by observation and experiment.

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Daniel T. wrote:

> In article <468s1qF9ru5hU1@individual.net>,
>  Dietmar Kuehl <dietmar_kuehl@yahoo.com> wrote:
>
>> JustSomeGuy wrote:
>> > This is what I've written but I'm not sure if I've garanteed to have
>> > the c_str() method return a buffer that is null padded.
>>
>> The method 'c_str()' will return a pointer to a null-terminated
>> representation of the 'std::string's content. That is, you will
>> have an extra null-character tagged on to the 'std::string's
>> content. If the 'std::string's content contains null-characters,
>> you cannot process the result of 'c_str()' with the 'str...()'
>> functions because these might stop at the first embedded
>> null-character. Thus, you probably should use the 'data()' method
>> instead because this has the same effect as 'c_str()' except that
>> it does not add an extra null-character.
>
> Let's say I have a string class that doesn't hold its data in a
> contiguous array but still wants to conform to the standard. This would
> mean I have to create an array and fill it whenever c_str is called (and
> I'm free to delete it whenever a non-const member-function is called.)
>
> Would my class be standard conforming if I only made a c_str array up to
> the first null? (I expect that data would have to have all the
> characters.)
>
> In other words given:
>
> int main()
> {
>    std::string s = "Hello! World";
>    s[6] = 0;
>    const char* foo = s.c_str();
>    char bar[6];
>    std::strcpy( bar, foo + 7 );
>    std::cout << bar;
> }
>
> Does the standard define the output of the above program?
>
>

The standard specifies:

21.3.6/1   const charT* c_str() const;
Returns: A pointer to the initial element of an array of length size() + 1
whose first size() elements equal the corresponding elements of the string
controlled by *this and whose last element is a null character specified by
charT().


Thus, you are not allowed to stop at the first 0 char. The size and contents
of the array pointed to by the return value of c_str() are completely
specified.


Best

Kai-Uwe Bux

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