Re: 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  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
--
_
vita es estrany
spir.wikidot.com

Re: use of C memmove

[Steven Schveighoffer]

On Thu, 07 Apr 2011 14:44:28 -0400, Kagamin  wrote:


spir Wrote:


 // If move down, compress array.
 if (offset < 0)
 elements.length += offset;


ow, addAssign works on length?


Since 12/09 :)

http://www.digitalmars.com/d/2.0/changelog.html#new2_037

-Steve

Re: use of C memmove

[Kagamin]

spir Wrote:

>  // If move down, compress array.
>  if (offset < 0)
>  elements.length += offset;

ow, addAssign works on length?

Re: use of C memmove

[Steven Schveighoffer]

On Thu, 07 Apr 2011 13:09:05 -0400, spir  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);

-Steve