core.stdc.stdlib._compare_fp_t and qsort

[Joe]

On Sunday, 18 March 2018 at 13:10:08 UTC, Dmitry Olshansky wrote:
> Do this to get the usual ptr + length:
>
> sort!((a, b) => to!string((*a).name) < 
> to!string((*b).name))(recs[]);
>
> Also to!string would be computed on each compare anew. May want 
> to use schwartzSort to avoid that, on 10 elements there is no 
> real difference though.

The 10 elements are just because it's a small test program.

What does changing "recs" to "recs[]" as the argument actually 
do?  Does it duplicate the fixed array on the fly? [I guess I 
have to study more!]

The change does pass the compiler, but at runtime it causes a 
segfault.  The next to last frame in the backtrace shows (having 
changed from to!string to fromStringz and using a string template 
instead of a lambda):

#6  0x0000555555565760 in 
std.algorithm.sorting.sort!("fromStringz((*a).name.ptr) < 
fromStringz((*b).name.ptr)", 0, 
testd.Record*[]).sort(testd.Record*[]) (r=...)

Then it goes through quickSortImpl, shortSort and sort5, moving 
on to either std.functional.binaryFun or processing of the 
lambda, with a and b equal to 0, ending with a segfault in a ?? 
call from fromStringz or in memcpy called from object._dup (in 
the to!string case).