KDB C++ API: creating a list of strings

Question

I am failing to create a list of strings in KDB C++ API. This is what I am doing:

 K lst = ktn(KC,0);
 jk(&lst, kp((S)"str_1")); 
 jk(&lst, kp((S)"str_2"));
 r1(lst);
 k(h, (S)"{show type x}" , lst, (K)0);
 r1(lst);
 k(h, (S)"{show count x}", lst, (K)0);
 r1(lst);
 k(h, (S)"{show x}"      , lst, (K)0);

The output

10h
2
"\260\260"

Where instead of "\260\260" could be some other random string repeated twice. It seems, I do create a list of strings, but the list contains rubbish for whatever reason. Could you please help me to understand what I am doing wrong here?

Thank you for your help!

MdSalih · Accepted Answer · 2017-04-28 22:25:21Z

You're initialising the list with type char (KC), so this will be a char list, not a string list.

A string list is a mixed type list, as it a list of list of chars in Kdb. Therefore, you need to initialise the list with type 0 (mixed list type).

Example C code - strList.c:

#define KXVER 3
#include "k.h"

K createStrListStatic(K x){
  K strList = ktn(0,2);
  kK(strList)[0] = kp("hello");
  kK(strList)[1] = kp("world");
  return strList;
}

K createStrListDynamic(K x){
  K strList = ktn(0,1);
  kK(strList)[0] = kp("hello");
  js(&strList, (S)kp("world"));
  return strList;
}

Example Q code to load the lib & call C funcs - strList.q:

createStrListStatic:`:strList 2:(`createStrListStatic;1);
createStrListDynamic:`:strList 2:(`createStrListDynamic;1);

-1 "\ncreateStrListStatic";
-1 "\t",.Q.s1 createStrListStatic[];
-1 "\ncreateStrListDynamic";
-1 "\t",.Q.s1 createStrListDynamic[];

Compile and run as follows:

$ gcc -shared -m32 -fPIC strList.c -o strList.so && LD_LIBRARY_PATH="." q strList.q
KDB+ 3.4 2016.10.27 Copyright (C) 1993-2016 Kx Systems
l32/ 8()core 7982MB salih glyph01 127.0.1.1 NONEXPIRE


createStrListStatic
        ("hello";"world")

createStrListDynamic
        ("hello";"world")

Collectives™ on Stack Overflow

KDB C++ API: creating a list of strings

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related