## digitalmars.D.learn - strings

• rko (8/8) May 19 2005 hi,
• Ben Hinkle (18/27) May 19 2005 I'll answer this in two ways:
• rko (7/39) May 19 2005 thanx a million. i know i am a nuisance but how does this work?
• Thomas Kuehne (9/13) May 19 2005 -----BEGIN PGP SIGNED MESSAGE-----
• Jim H (9/12) May 23 2005 Yes, as a new user, I thought it was a bit odd that the second index of ...
• Lars Ivar Igesund (8/25) May 23 2005 Because you need to be able to specify zero-length slices. If you have a...
• Derek Parnell (10/12) May 23 2005 Just being a bit pedantic, but this only applies to 0-based indexing.
• Lars Ivar Igesund (2/10) May 24 2005 Yes, of course, but we are learning D, here, aren't we? :)
• Derek Parnell (6/18) May 24 2005 Oh yeah, that's right. I keep forgetting even the simplest of things. ;-...
• Andrew Fedoniouk (29/32) May 19 2005 Probably this "zoo" (below) from Harmonia will also help you:
```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
"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
```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
Thomas Kuehne <thomas-dloop kuehne.this-is.spam.cn> writes:
```-----BEGIN PGP SIGNED MESSAGE-----
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")

-----BEGIN PGP SIGNATURE-----

iD8DBQFCjKZC3w+/yD4P9tIRApSbAKDExZY5iix4zRWHPkmqmkAcTW0KHACfYMVS
=AoDi
-----END PGP SIGNATURE-----
```
May 19 2005
"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
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
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
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
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
"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?

module harmomia.utils.string;

import std.string;
import std.utf;

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

wchar[] a2wz( char[] a ) { return zstr!(wchar)(a2w(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