Mismatch between C++ symbols and Q symbols

Question

I'm having some trouble when returning symbols from C++ code. I made a small example that illustrates the problem.

We export the following function:

extern "C" __declspec(dllexport) K getSym(K x) {
    return ks((S)"sym");
}

And then call it from Q:

q)asdf:(`our_dll 2:(`getSym;1))[1]
q)asdf
`sym
q)asdf = `sym
0b
q)asdf = `$string asdf
0b
q)0N!asdf
`sym
`sym
q)(string asdf) = (string `sym)
111b

Why are the two values unequal?

This is 32-bit KDB+ 3.2.

sometimes the console can obscure the actual underlying shape/type of a variable. 0N! will display the true value — terrylynch, Apr 07 '15 at 21:04
I added the output of `0N!asdf` to the question. @KhouriGiordano , which version of KDB are you using? — , Apr 08 '15 at 13:30
It's Win32 and on start-up, Q says "KDB+ 3.2 2015.04.07". I got the `k.h` and `q.lib` files that are linked from [the wiki](http://code.kx.com/wiki/Cookbook/ExtendingWithC). I had never heard of Q until this question, tho I've made plenty of dynamically loaded DLLs. — Khouri Giordano, Apr 08 '15 at 20:54

score 0 · Answer 1 · answered Oct 03 '15 at 00:17

0

If you use a version of q prior to 2.4, you need to intern C string using the ss() function before passing it to ks(). You should not see this problem with the recent versions.

answered Oct 03 '15 at 00:17

Alexander Belopolsky

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Mismatch between C++ symbols and Q symbols

1 Answers1