use of C memmove

[spir]

On 04/07/2011 08:12 PM, Steven Schveighoffer wrote:
> On Thu, 07 Apr 2011 13:09:05 -0400, spir <denis.spir at gmail.com> wrote:
>
>> Hello,
>>
>> I'm trying to use C's memmove as a tool to delete or insert a slice from/into
>> an array. But I cannot manage to do it: systematic segmentation fault.
>> What is wrong below?
>>
>> import std.c.string : memmove;
>> // void *memmove(void *dest, const void *src, size_t n);
>>
>> void moveEnd (E) (E[] elements, size_t start, int offset) {
>> // Length must be known before possible extension.
>> auto length = elements.length;
>>
>> // If move up, extend array to make place.
>> if (offset > 0)
>> elements.length += offset;
>>
>> // Move slice.
>> auto dest = cast(void*)(&(elements[start + offset]));
>> auto source = cast(void*)(&(elements[start]));
>> size_t size = length - start;
>> memmove(dest, source, size); // segfault ***
>>
>> // If move down, compress array.
>> if (offset < 0)
>> elements.length += offset;
>> }
>>
>> unittest {
>> string s = "012--3456789";
>> // Remove slice.
>> s.moveEnd(5, -2);
>> writeln(s);
>> }
>
> Two problems. One is, the memmove size_t n is number of *bytes*, not number of
> elements as you have expected. You probably would have noticed this quickly if
> the other problem wasn't there.
>
> The other problem is, strings literals are immutable. On Windows, this code may
> have worked, but Linux protects the pages of static data, so writing to a
> string literal creates a seg fault.
>
> Try this:
>
> auto s = "012--3456789".dup; // convert to char[]
>
> To fix first problem use memmove(dest, source, size * (E).sizeof);

Thank you very much, Steven!

Denis
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