c++ grab in position signal

error: implicit declaration of function ‘kill’

#include <stdio.h>    
#include <stdlib.h> 
#include <stdint.h>   
#include <string.h>   
#include <unistd.h>   
#include <fcntl.h>    
#include <errno.h>    
#include <signal.h>



int main(void)
{
    kill(17175, SIGUSR1);
    printf("\n signal send \n");
    return 0;
}

component threadkill                  "This component waits for machine.in-position and kills a pre-defined thread process";

pin in bit commandfinished = 1        "signal last command completed - connect to motion.in-position";
pin in bit homed = 0                  "signal that machine is homed and ready for commands - connect to last axis to home - halui.joint.2.is-homed";
pin in bit machineon = 0              "signal to ensure machine is on - connect to halui.machine.is-on"; 
option singleton yes;               
option userspace yes;

author "ArcEye <arceyeATmgwareDOTcoDOTuk>";
license "GPL";
;;

#include <stdio.h>    /* Standard input/output definitions */
#include <stdlib.h> 
#include <stdint.h>   /* Standard types */
#include <string.h>   /* String function definitions */
#include <unistd.h>   /* UNIX standard function definitions */
#include <fcntl.h>    /* File control definitions */
#include <errno.h>    /* Error number definitions */
#include <signal.h>

int done = 0;

void adios(int sig) { done = 1; }


void user_mainloop(void)
{
int progress = 1;  // start at a state which requires commandfinished to be false before doing anything
int status_changed = 0;
   
signal(SIGINT, adios);
signal(SIGTERM, adios);
      
    while(!done)
        {
        usleep(250000);
        
        FOR_ALL_INSTS()  
            { 
            if(homed && machineon)
                {
                switch(progress)
                    {
                    case 0: // commandfinished will be true until a command has begun
                            // prevent cycling by having a status_changed flag which is set when it
                            // is not true, allowing another kill() to be sent
                            
                            if(commandfinished && status_changed)
                                {
                                kill(17175, SIGUSR1);
                                //fprintf(stderr, "\nKill() called\n");
                                status_changed = 0;
                                progress = 1;
                                }
                            break;                
                            
                    case 1: if(!commandfinished)
                                {
                                status_changed = 1;
                                progress = 0;
                                }
                        
                    default:
                            break;               
                
                    }
                }
            }
        }
    exit(0);
}

sudo comp --install /home/linuxcnc/thread.comp
sudo comp --compile /home/linuxcnc/thread.comp

k1@k1-desktop:~$ sudo comp --compile '/home/k1/linuxcnc/PROVA1/threadkill.comp' gcc -Os -g -I. -I/usr/realtime-2.6.32-122-rtai/include -I. -I/usr/realtime-2.6.32-122-rtai/include -D_FORTIFY_SOURCE=0 -mhard-float -DRTAI=3 -fno-fast-math -mieee-fp -fno-unsafe-math-optimizations -DRTAPI -D_GNU_SOURCE -Drealtime -D_FORTIFY_SOURCE=0 -D__MODULE__ -I/usr/include/linuxcnc -Wframe-larger-than=2560 -URTAPI -U__MODULE__ -DULAPI -Os  -o GFXTH_kill /tmp/tmp118qzS/GFXTH_kill.c -Wl,-rpath,/lib -L/lib -llinuxcnchal 

k1@k1-desktop:~$ sudo comp --install '/home/k1/linuxcnc/PROVA1/threadkill.comp' gcc -Os -g -I. -I/usr/realtime-2.6.32-122-rtai/include -I. -I/usr/realtime-2.6.32-122-rtai/include -D_FORTIFY_SOURCE=0 -mhard-float -DRTAI=3 -fno-fast-math -mieee-fp -fno-unsafe-math-optimizations -DRTAPI -D_GNU_SOURCE -Drealtime -D_FORTIFY_SOURCE=0 -D__MODULE__ -I/usr/include/linuxcnc -Wframe-larger-than=2560 -URTAPI -U__MODULE__ -DULAPI -Os  -o GFXTH_kill /tmp/tmpf_O0kT/GFXTH_kill.c -Wl,-rpath,/lib -L/lib -llinuxcnchal 
k1@k1-desktop:~$ 

loadrt threadkill

loadusr -W threadkill

net inpos motion.in-position =>  threadkill.killsignalstart

loadusr -W threadkill

net sig1 threadkill.commandfinished <= motion.in-position
net sig2 threadkill.homed <= halui.joint.2.is-homed
net sig3 threadkill.machineon <= halui.machine.is-on