On 02/04/2021 5:32 PM, mw wrote:
> ---
> import std;
> import std.conv : text;
> 
> 
> void main()
> {
>     char[6] s;
>     s = "abc";
>     writeln(s, s.length);  // abc6, ok it's the static array's length
> 
>     string t = text("head-", s, "-tail");
>     writeln(t, t.length);  // head-abc-tail16, why?
assert(t[9] == '\0');
> }
> ---

On Friday, 2 April 2021 at 04:36:01 UTC, rikki cattermole wrote:
> On 02/04/2021 5:32 PM, mw wrote:
>> ---
>> import std;
>> import std.conv : text;
>> 
>> 
>> void main()
>> {
>>     char[6] s;
>>     s = "abc";
>>     writeln(s, s.length);  // abc6, ok it's the static array's length
>> 
>>     string t = text("head-", s, "-tail");
>>     writeln(t, t.length);  // head-abc-tail16, why?
> assert(t[9] == '\0');
>> }
>> ---

I don't get it, what do you mean by the assertion:


assert(t[9] == '\0');


t == "head-abc-tail"

On 02/04/2021 5:38 PM, mw wrote:
> On Friday, 2 April 2021 at 04:36:01 UTC, rikki cattermole wrote:
>> On 02/04/2021 5:32 PM, mw wrote:
>>> ---
>>> import std;
>>> import std.conv : text;
>>>
>>>
>>> void main()
>>> {
>>>     char[6] s;
>>>     s = "abc";
>>>     writeln(s, s.length);  // abc6, ok it's the static array's length
>>>
>>>     string t = text("head-", s, "-tail");
>>>     writeln(t, t.length);  // head-abc-tail16, why?
>> assert(t[9] == '\0');
>>> }
>>> ---
> 
> I don't get it, what do you mean by the assertion:
> 
> 
> assert(t[9] == '\0');
> 
> 
> t == "head-abc-tail"

Not all characters can be printed such as NULL.

[104, 101, 97, 100, 45, 97, 98, 99, 0, 0, 0, 45, 116, 97, 105, 108]

On Fri, Apr 02, 2021 at 04:32:53AM +0000, mw via Digitalmars-d-learn wrote: [...]
> ---
> import std;
> import std.conv : text;
> 
> 
> void main()
> {
>     char[6] s;
>     s = "abc";
>     writeln(s, s.length);  // abc6, ok it's the static array's length
> 
>     string t = text("head-", s, "-tail");
>     writeln(t, t.length);  // head-abc-tail16, why?
> }
> ---
> 
> Why the last output is 16 instead of 13, t's type is string here.

Because `s` contains 6 chars, and you only assigned 3 of them, so there are 3 trailing null bytes that are inserted before "-tail". Null bytes don't print anything, so you don't see them when printed as a string, but if you cast it to ubyte[], you will see them:

	writefln("%(%02X %)", t);
	// Prints: 68 65 61 64 2D 61 62 63 00 00 00 2D 74 61 69 6C

Remember, this is D, not C. Strings are not terminated by nulls, so appending the static array will append all 6 chars, including the nulls.


T

-- 
Holding a grudge is like drinking poison and hoping the other person dies. -- seen on the 'Net

On 02/04/2021 5:51 PM, mw wrote:
> Then how can I construct `t`? to make this assertion true:
> 
>     assert(t == "head-abc-tail");  // failed!

Slice it.

string t = text("head-", s[0 .. 3], "-tail");

http://ddili.org/ders/d.en/slices.html