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digitalmars.D.learn - strings

reply rko <rko_member pathlink.com> writes:
hi,

how does one convert strings from 'c' strings to 'd' strings and viceversa?

char[] x;
//'C' 
char y[128];

x = y and y = x?

thanx

rko
May 19 2005
next sibling parent reply "Ben Hinkle" <ben.hinkle gmail.com> writes:
"rko" <rko_member pathlink.com> wrote in message 
news:d6hgl9$19vg$1 digitaldaemon.com...

 hi,

 how does one convert strings from 'c' strings to 'd' strings and 
 viceversa?

 char[] x;
 //'C'
 char y[128];

 x = y and y = x?

 thanx

 rko


I'll answer this in two ways:
1) to convert a D string to a C string call std.string.toStringz. To convert 
a C string to a D string write y[0 .. strlen(y)].
2) To copy data from one array to another (eg between char arrays) use
  y[0 .. numel] = x[0 .. numel];
where numel is the number of elements to copy.

The reason to separate converting C/D strings and copying data is that the 
conversions can share data with the original string and don't necessarily 
copy data - since the conversion has to do with 0-termination and length 
computation.
Back you your variables, if you have a C string stored in y then to get a D 
string slice of it run y[0 .. strlen(y)]. If you have a D string in x and 
you want to copy it to y and make it a C string then run
  int numel = x.length>127?127:x.length;
  y[0 .. numel] = x[0 .. numel];
  y[numel] = 0;
May 19 2005
parent reply rko <rko_member pathlink.com> writes:
In article <d6i0hv$1nnp$1 digitaldaemon.com>, Ben Hinkle says...

"rko" <rko_member pathlink.com> wrote in message 
news:d6hgl9$19vg$1 digitaldaemon.com...

 hi,

 how does one convert strings from 'c' strings to 'd' strings and 
 viceversa?

 char[] x;
 //'C'
 char y[128];

 x = y and y = x?

 thanx

 rko


I'll answer this in two ways:
1) to convert a D string to a C string call std.string.toStringz. To convert 
a C string to a D string write y[0 .. strlen(y)].
2) To copy data from one array to another (eg between char arrays) use
  y[0 .. numel] = x[0 .. numel];
where numel is the number of elements to copy.

The reason to separate converting C/D strings and copying data is that the 
conversions can share data with the original string and don't necessarily 
copy data - since the conversion has to do with 0-termination and length 
computation.
Back you your variables, if you have a C string stored in y then to get a D 
string slice of it run y[0 .. strlen(y)]. If you have a D string in x and 
you want to copy it to y and make it a C string then run
  int numel = x.length>127?127:x.length;
  y[0 .. numel] = x[0 .. numel];
  y[numel] = 0; 


thanx a million. i know i am a nuisance but how does this work?

char[] a; // will get somewhere the content "test string"

now i would like to compare such as 

if(a[0..3] == "test") { ....

and that does not work.


rko
May 19 2005
parent reply Thomas Kuehne <thomas-dloop kuehne.this-is.spam.cn> writes:
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Hash: SHA1

rko schrieb am Thu, 19 May 2005 12:40:46 +0000 (UTC):

 thanx a million. i know i am a nuisance but how does this work?

 char[] a; // will get somewhere the content "test string"

 now i would like to compare such as 

 if(a[0..3] == "test") { ....


	if(a[0..4] == "test")



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kNx/e4o77VPTqvnaDZdB59o=
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May 19 2005
parent reply "Jim H" <jimh nowhere.com> writes:
"Thomas Kuehne" <thomas-dloop kuehne.this-is.spam.cn> wrote in message 
news:d8p9i2.496.thomas-dloop laermschleuder.kuehne.cn...

 if(a[0..3] == "test") { ....


 if(a[0..4] == "test")


Yes, as a new user, I thought it was a bit odd that the second index of a 
slicing index was non-inclusive. It feels like you're indexing off the end 
of the array. As a C/C++ programmer, I'm fine with thinking in terms of 
(length-1) for zero-based indexing. It seemed to me that something like 
a[2..2] should return a one-element array consisting of index 2 rather than 
an empty array. But I suppose there must be a good rationale for it.

Jim
May 23 2005
parent reply Lars Ivar Igesund <larsivar igesund.net> writes:
Jim H wrote:


 
 "Thomas Kuehne" <thomas-dloop kuehne.this-is.spam.cn> wrote in message
 news:d8p9i2.496.thomas-dloop laermschleuder.kuehne.cn...

 if(a[0..3] == "test") { ....


 if(a[0..4] == "test")


 
 Yes, as a new user, I thought it was a bit odd that the second index of a
 slicing index was non-inclusive. It feels like you're indexing off the end
 of the array. As a C/C++ programmer, I'm fine with thinking in terms of
 (length-1) for zero-based indexing. It seemed to me that something like
 a[2..2] should return a one-element array consisting of index 2 rather
 than an empty array. But I suppose there must be a good rationale for it.
 
 Jim


Because you need to be able to specify zero-length slices. If you have an
array 'things', where you want to remove element 'ẍ́', where 0 > x >
things.length, you can do this:

things = things[0..x] ~ things[(x + 1)..things.length];

If [0..0] were the first element, you wouldn't be able to remove it by
setting x = 0;

Lars Ivar Igesund
May 23 2005
parent reply Derek Parnell <derek psych.ward> writes:
On Mon, 23 May 2005 22:32:08 +0200, Lars Ivar Igesund wrote:

[snip]


 If [0..0] were the first element, you wouldn't be able to remove it by
 setting x = 0;


Just being a bit pedantic, but this only applies to 0-based indexing. 

For languages that use 1-based indexing, they signal a zero length slice by
using the form [x ..x-1], thus in those languages, [1..1] is a one-element
slice and [1..0] is a zero length slice.

-- 
Derek Parnell
Melbourne, Australia
24/05/2005 7:46:54 AM
May 23 2005
parent reply Lars Ivar Igesund <larsivar igesund.net> writes:
Derek Parnell wrote:


 On Mon, 23 May 2005 22:32:08 +0200, Lars Ivar Igesund wrote:
 
 [snip]
 

 If [0..0] were the first element, you wouldn't be able to remove it by
 setting x = 0;


 
 Just being a bit pedantic, but this only applies to 0-based indexing.


Yes, of course, but we are learning D, here, aren't we? :)
May 24 2005
parent Derek Parnell <derek psych.ward> writes:
On Tue, 24 May 2005 21:09:21 +0200, Lars Ivar Igesund wrote:


 Derek Parnell wrote:
 

 On Mon, 23 May 2005 22:32:08 +0200, Lars Ivar Igesund wrote:
 
 [snip]
 

 If [0..0] were the first element, you wouldn't be able to remove it by
 setting x = 0;


 
 Just being a bit pedantic, but this only applies to 0-based indexing.


 
 Yes, of course, but we are learning D, here, aren't we? :)


Oh yeah, that's right. I keep forgetting even the simplest of things. ;-)

-- 
Derek Parnell
Melbourne, Australia
25/05/2005 7:28:48 AM
May 24 2005
prev sibling parent "Andrew Fedoniouk" <news terrainformatica.com> writes:
"rko" <rko_member pathlink.com> wrote in message 
news:d6hgl9$19vg$1 digitaldaemon.com...

 hi,

 how does one convert strings from 'c' strings to 'd' strings and 
 viceversa?


Probably this "zoo" (below) from Harmonia will also help you:

module harmomia.utils.string;

import std.string;
import std.utf;

char[]  w2a( wchar[] w )  { return toUTF8(w); }
char[]  w2az( wchar[] w ) { return zstr!(char)(w2a(w)); }
char[]  wz2a( wchar* w )  { return toUTF8( wz2w(w) ); }
char[]  wz2az( wchar* w ) { return zstr!(char)(wz2a(w)); }

wchar[] a2w( char[] a )  { return toUTF16(a); }
wchar[] a2wz( char[] a ) { return zstr!(wchar)(a2w(a)); }
wchar[] az2w( char* a )  { return toUTF16( az2a(a) ); }
wchar[] az2wz( char* a ) { return zstr!(wchar)(az2w(a)); }

wchar[] wz2w( wchar* w ) { return w? w[0..wcslen(w)]: null; }
char[]    az2a( char* a ) { return a? a[0..strlen(a)]: null; }

wchar[] w2wz( wchar[] w ) { return zstr!(wchar)(w); }
char[]    a2az( char[] a )   { return zstr!(char)(a); }

template zstr(CHAR) // in-place zero terminate
{
  CHAR[] zstr(CHAR[] chars) // returns zero terminated string
  {
    uint l = chars.length;
    chars.length = l + 1;
    chars[l] = 0;
    chars.length = l;
    return chars;
  }
}
May 19 2005