Linux development

Denne side skal ses som et linux modstykke til MFC siden.

Application framework og GUI

Skal du lave noget C++ til linux er der mange toolkits at vælge i mellem. Men du vil sikkert få mest success med enten wxWidgets eller Qt.

Daemon

Hvis at man laver et server program til linux, vil man som regel gerne at processen kører i baggrunden - her er et eksempel på hvordan at det kan laves:

Kode

#include <signal.h>
#include <fcntl.h>

#define LOCKFILE "/tmp/myapp.lock"

#define FORK_ERROR -1
#define CANT_OPEN_LOCK -2
#define ALREADY_LOCKED -3
#define daemon_shutdown(x) exit(x)

void log_message(const char *);
 
void signal_handler(int sig)
{
	switch(sig) {
		case SIGHUP:
			log_message("hangup signal catched");
			break;
		case SIGTERM:
			log_message("terminate signal catched...exiting");
			unlink(LOCKFILE);
			daemon_shutdown(0);
			break;
	}
}


void daemonize()
{	
	int i, lfp;
	char str[10];
	
	if (getppid() == 1) /* already a daemon */
		return;
		
	i=fork();
	
	if (i<0) /* fork error */
		daemon_shutdown(FORK_ERROR);
	if (i>0) /* parent exits */
		daemon_shutdown(0);
	/* child daemon continues */
	
	setsid(); /* obtain a new process group */
	
	for (i=getdtablesize(); i>=0; --i)
		close(i); /*close all descriptors*/
		
	i=open("/dev/null", O_RDWR); /* handle std. io */
	dup(i);
	dup(i);
	
	umask(027); /* set newly created file permissions */
	
	chdir("/tmp"); /* change running directory*/
	
	/*attempt to create lockfile and put a file-lock on it*/
	lfp=open(LOCKFILE, O_RDWR|O_CREAT, 0640);
	if (lfp<0) /* can not open */
		daemon_shutdown(CANT_OPEN_LOCK);
	if (lockf(lfp,F_TLOCK,0) < 0) /* can not lock */
		daemon_shutdown(ALREADY_LOCKED);
	
	/* first instance continues */
	sprintf(str, "%d\n", getpid() ); /* record pid to lockfile */
	write(lfp, str, strlen(str) );
	signal(SIGCHLD, SIG_IGN); /* ignore child */
	signal(SIGTSTP, SIG_IGN); /* ignore tty signals */
	signal(SIGTTOU, SIG_IGN);
	signal(SIGTTIN, SIG_IGN);
	signal(SIGHUP, signal_handler); /* catch hangup signal */
	signal(SIGTERM, signal_handler); /* catch kill signal */	

	/*this program is now a daemon*/
}