something weird with strerror_r

[CodeSun via Digitalmars-d]

On Thursday, 29 January 2015 at 15:25:09 UTC, Mike Parker wrote:
> On 1/29/2015 11:40 PM, CodeSun wrote:
>> Recently, I found something really weird when I use strerror_t 
>> function
>> which is declared inside std.c.string.
>> The code snippet is listed below:
>> import std.c.string;
>> import core.stdc.errno;
>>
>> void main() {
>>     import std.stdio;
>>     char[128] buf;
>>     strerror_r(errno, buf.ptr, buf.sizeof);
>>     writeln(cast(string)buf);
>> }
>>
>> The terminal should print "Success" with errno=0, but in this 
>> example,
>> the result is
>> "��������������������������������������������������������������������������������������������������������������������������������".
>>
>> I test this snippet both on Archlinux and Ubuntu 14.04.1, and 
>> the result
>> is same. If there is someone can help me?
>> I wanna know if it is my mistake or it is just a bug.
>> Thx!
>
> The GNU version of strerror_r is documented as returning
>
> "a pointer to a string containing the error message. This may 
> be either a pointer to a string that the function stores in 
> buf, or a pointer to some (immutable) static string (in which 
> case buf is unused)."
>
> So I think what you may have been seeing in this case is that 
> it was returning a static string, your buffer remained empty 
> and the writeln was printing a bunch of 0xFFs. Probably this is 
> a better way to handle it:
>
> void main()
> {
>    import core.stdc.errno : errno;
>    import std.c.string : strerror_r;
>
>    // Static arrays are initialized to T.init. For
>    // char, T.init is 0xFF, *not* 0. The initializer
>    // here will fill the array with 0.
>    char[ 128 ] buf = 0;
>    auto cstr = strerror_r( errno, buf.ptr, buf.sizeof );
>
>    // Slice the C string with fromStringz. Unlike to!string, 
> this
>    // does not allocate or copy.
>    import std.string : fromStringz;
>    writeln( cstr.fromStringz() );
> }

Yes, you are right, when I printed the cstr, I got the result I 
wanted. In fact, I neglect the detail you attached here from the 
manual.
Thx!