• MacAsm (54/54) Aug 26 2014 It maybe trivial to most of you but I don't know how do this
• H. S. Teoh via Digitalmars-d (8/14) Aug 26 2014 [...]
• MacAsm (4/19) Aug 27 2014 Thanks. This is exactly what I was worried about. If no string
• anonymous (18/25) Aug 26 2014 If you're worried that this copies the string data, it doesn't. A

"MacAsm" <jckj33 gmail.com> writes:

It maybe trivial to most of you but I don't know how do this 
avoiding string duplications. Can someone help me?

char *str = "foobaa";
char *p = str;
char *prev = NULL;

int go(void)
{
    int ch;

    ch = top();
    move(1);
    return ch;
}

int top(void)
{
   retun *p;
}

void back(void)
{
    p = prev;
}

void move(int n)
{
    prev = p;
    p += n;
}

in D, I can wrote as following:

string str = "foobaa";
string prev;

dchar go()
{
   dchar ch = top();
   move(1);
   return ch;
}

dchar top()
{
   return str.front;
}

void move(int n)
{
   prev = str; // <- I want to avoid this string duplication did 
in every move() call
   foreach(i; 0 .. n) { // <- improve this is welcome too.
       str.popFront();
    }
}

void back()
{
   str = prev;
}


Here's (for better code reading readability) C and D codes on 
pastebin,respectively :

http://pastebin.com/J3vzP3UK

http://pastebin.com/C0NyNjY0

"H. S. Teoh via Digitalmars-d" <digitalmars-d puremagic.com> writes:

On Tue, Aug 26, 2014 at 08:58:13PM +0000, MacAsm via Digitalmars-d wrote:
 It maybe trivial to most of you but I don't know how do this avoiding
 string duplications. Can someone help me?

[...]
 in D, I can wrote as following:

[...]
 void move(int n)
 {
   prev = str; // <- I want to avoid this string duplication did in every
move() call

This does not duplicate the string. You may find this article helpful:

	http://dlang.org/d-array-article.html


T

-- 
Genius may have its limitations, but stupidity is not thus handicapped. --
Elbert Hubbard

"MacAsm" <jckj33 gmail.com> writes:

On Tuesday, 26 August 2014 at 21:29:04 UTC, H. S. Teoh via 
Digitalmars-d wrote:
 On Tue, Aug 26, 2014 at 08:58:13PM +0000, MacAsm via 
 Digitalmars-d wrote:
 It maybe trivial to most of you but I don't know how do this 
 avoiding
 string duplications. Can someone help me?

 [...]
 in D, I can wrote as following:

 [...]
 void move(int n)
 {
   prev = str; // <- I want to avoid this string duplication 
 did in every move() call

 This does not duplicate the string. You may find this article 
 helpful:

 	http://dlang.org/d-array-article.html

Thanks. This is exactly what I was worried about. If no string 
duplciation is done I think this D code is just fine...

"anonymous" <anonymous example.com> writes:

On Tuesday, 26 August 2014 at 20:58:15 UTC, MacAsm wrote:
 string str = "foobaa";
 string prev;

[...]
   prev = str; // <- I want to avoid this string duplication did 
 in every move() call

If you're worried that this copies the string data, it doesn't. A 
dynamic array (which string is) is a pair of a pointer and a 
length, and only those are copied.

   foreach(i; 0 .. n) { // <- improve this is welcome too.
       str.popFront();
    }

You can use std.range.popFrontN: str.popFrontN(n);

Also, there are two (maybe more) subtle differences between the D
code and the C code, of which you may not be aware:
1) The D version assumes UTF8. A char is a UTF8 code unit in D,
whereas in C it's just a byte. In D that would be (u)byte. But
char is fine when you're indeed working on UTF8.
2) The D version decodes to code points (dchar). This means e.g.,
that the D version potentially reaches the end of the string in
fewer `go` calls than the C version.

Finally, the "learn" board [1] would have been a better place for 
this post.  No turning back now, and it's not a big deal, but 
next time maybe post there.

[1] http://forum.dlang.org/group/digitalmars.D.learn