# c extension causing segmentation fault **URL:** \ **Category:** Community Support\ **Tags:** kdb-and-q\ **Created:** [December 29, 2013, 5:24pm UTC](https://forum.kx.com/t/c-extension-causing-segmentation-fault/8559 "2013-12-29T17:24:00Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![adnan\_gazi01](https://avatars.discourse-cdn.com/v4/letter/a/48db29/32.png) [@adnan\_gazi01](https://forum.kx.com/u/adnan_gazi01)\ **Post date:** [December 29, 2013, 5:24pm UTC](https://forum.kx.com/t/c-extension-causing-segmentation-fault/8559/1 "2013-12-29T17:24:00Z")
I’ve written a shared object in C containing a function that takes a K int and K symbol as args, and starts a java program using those variables as its parameters by calling system(). It’s giving me a segmentation fault when I call the q function that calls the shared object, and q decides to kill it after telling me it encountered a fatal error. Ive stripped the C code down but it seems to be the case that the error stems from using the 2 K parameters in the SO. The C code and q error log are pasted below. I’m running the 32 bit trial q and have compiled the shared object as 32 bit. C code: #define KXVER 3 #include “k.h” #include \ #include \ K start(K port, K dict) {                int p = port-\>i;     char \*d = dict-\>s;     printf(“Port: %d, Dict: %s”,p,d);     char \*command = (“java -jar $QHOME/l32/gui.jar %d %s”);     int outsize = sizeof(command) + sizeof(d) + 4;     char \*out = malloc(outsize);     sprintf(out, command, p, d);           system(out);     return 0; } And q’s error is this: Sorry, this application or an associated library has encountered a fatal error and will exit. If known, please email the steps to reproduce this error to [tech@kx.com](mailto:tech@kx.com) with a copy of the kdb+ startup banner. Thank you. q() [0x80af848] [0xf7726410] /lib32/libc.so.6(\_IO\_vfprintf+0x4519) [0xf7527b79] /lib32/libc.so.6(\_IO\_printf+0x2f) [0xf752d44f] /home/adnan/q/l32/kge.so(start+0x40) [0xf772262b] q(dlc+0xbf) [0x80ae92f] q() [0x8087e2c] q() [0x8088ccb] q() [0x8087b8c] q(tix+0x15d) [0x808992d] q(kx+0x1f) [0x808a0ff] q(f1+0x1a) [0x80669aa] q(c9+0x2f8) [0x80892e8] q(f2+0x93) [0x8066aa3] q() [0x804f1ad] rlwrap: warning: q killed by SIGSEGV. rlwrap has not crashed, but for transparency, it will now kill itself (without dumping core)with the same signal Segmentation fault The java program is meant to start a gui displaying the variables in namspace “dict” on port “port”. I’ve been developing it for a while now, and it works fine on its own. A shared object with no parameters calls the java program if I set the port and namespace myself, but otherwise it doesn’t seem to be working. Any help would be greatly appreciated. Thanks ---
**Author:** ![charlie1](https://avatars.discourse-cdn.com/v4/letter/c/ec9cab/32.png) [@charlie1](https://forum.kx.com/u/charlie1)\ **Post date:** [December 29, 2013, 6:06pm UTC](https://forum.kx.com/t/c-extension-causing-segmentation-fault/8559/2 "2013-12-29T18:06:00Z")
btw, have you tried the q command system? q)system"java …. &" In your c code, i think you have a bug with sizeof - should use strlen. ---
**Author:** ![adnan\_gazi01](https://avatars.discourse-cdn.com/v4/letter/a/48db29/32.png) [@adnan\_gazi01](https://forum.kx.com/u/adnan_gazi01)\ **Post date:** [December 29, 2013, 6:29pm UTC](https://forum.kx.com/t/c-extension-causing-segmentation-fault/8559/3 "2013-12-29T18:29:00Z")
AHHH no i hadn’t realised there was a system command. Damn. The system command works though, which is good. Is there a way to cast an integer or symbol as a string? so I can use it in the system call? The C function would’ve taken K objects ---
**Author:** ![charlie1](https://avatars.discourse-cdn.com/v4/letter/c/ec9cab/32.png) [@charlie1](https://forum.kx.com/u/charlie1)\ **Post date:** [December 29, 2013, 6:32pm UTC](https://forum.kx.com/t/c-extension-causing-segmentation-fault/8559/4 "2013-12-29T18:32:00Z")
q)string 1234 “1234” q)string `hello`world “hello” “world” ---
**Author:** ![adnan\_gazi01](https://avatars.discourse-cdn.com/v4/letter/a/48db29/32.png) [@adnan\_gazi01](https://forum.kx.com/u/adnan_gazi01)\ **Post date:** [December 29, 2013, 6:39pm UTC](https://forum.kx.com/t/c-extension-causing-segmentation-fault/8559/5 "2013-12-29T18:39:00Z")
Wow. Thanks a lot! this has really helped.