/* Open the device */
if ( (adhandle= pcap_open(d->name,
65536,
PCAP_OPENFLAG_PROMISCUOUS,
1000,
NULL,
errbuf)
) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not supported by WinPcap\n", d->name);
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
This code is in this.
I included pcap.h.
But I can't use pcap_open() function.
identifier "pcap_open" is undefined
Please help me.
Related
I needed a cheap way for my application to create a PDF file. So I'm using the print functions of the Windows API directly (CreateDC(), StartDoc(), StartPage(), EndPage(), EndDoc(), etc.), and selecting the Microsoft Print to PDF printer driver.
In addition, I found that if I set the lpszOutput member of the DOCINFOstructure to a filename, the driver will write the PDF file to the named file without prompting the user for a name.
So far, so good. But how do I know when the PDF file has been created? There are spooler APIs, but the driver isn't necessarily done just because the spooler is done. Or I could create a loop that looks for the file, but of course it will exist before it is actually done. I also thought about trying to put a lock on the file in my loop, which should fail if the file doesn't exist yet or is still being written to.
But I can't help but wonder if there's a more direct way to know when the PDF file is ready.
If you are using the GDI Print API (wingdi.h), then this link shows the sample code used to query the status of print jobs on a printer.
I'm including the code from the link, but you might want to read the article as well.
#include <Windows.h>
#include <wingdi.h>
BOOL GetJobs(HANDLE hPrinter, /* Handle to the printer. */
JOB_INFO_2 **ppJobInfo, /* Pointer to be filled. */
int *pcJobs, /* Count of jobs filled. */
DWORD *pStatus) /* Print Queue status. */
{
DWORD cByteNeeded,
nReturned,
cByteUsed;
JOB_INFO_2 *pJobStorage = NULL;
PRINTER_INFO_2 *pPrinterInfo = NULL;
/* Get the buffer size needed. */
if (!GetPrinter(hPrinter, 2, NULL, 0, &cByteNeeded)) {
if (GetLastError() != ERROR_INSUFFICIENT_BUFFER)
return FALSE;
}
pPrinterInfo = (PRINTER_INFO_2 *)malloc(cByteNeeded);
if (!(pPrinterInfo))
/* Failure to allocate memory. */
return FALSE;
/* Get the printer information. */
if (!GetPrinter(hPrinter,
2,
(LPSTR)pPrinterInfo,
cByteNeeded,
&cByteUsed)) {
/* Failure to access the printer. */
free(pPrinterInfo);
pPrinterInfo = NULL;
return FALSE;
}
/* Get job storage space. */
if (!EnumJobs(hPrinter,
0,
pPrinterInfo->cJobs,
2,
NULL,
0,
(LPDWORD)&cByteNeeded,
(LPDWORD)&nReturned)) {
if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
free(pPrinterInfo);
pPrinterInfo = NULL;
return FALSE;
}
}
pJobStorage = (JOB_INFO_2 *)malloc(cByteNeeded);
if (!pJobStorage) {
/* Failure to allocate Job storage space. */
free(pPrinterInfo);
pPrinterInfo = NULL;
return FALSE;
}
ZeroMemory(pJobStorage, cByteNeeded);
/* Get the list of jobs. */
if (!EnumJobs(hPrinter,
0,
pPrinterInfo->cJobs,
2,
(LPBYTE)pJobStorage,
cByteNeeded,
(LPDWORD)&cByteUsed,
(LPDWORD)&nReturned)) {
free(pPrinterInfo);
free(pJobStorage);
pJobStorage = NULL;
pPrinterInfo = NULL;
return FALSE;
}
/*
* Return the information.
*/
*pcJobs = nReturned;
*pStatus = pPrinterInfo->Status;
*ppJobInfo = pJobStorage;
free(pPrinterInfo);
return TRUE;
}
BOOL IsPrinterError(HANDLE hPrinter) {
JOB_INFO_2 *pJobs;
int cJobs,
i;
DWORD dwPrinterStatus;
/*
* Get the state information for the Printer Queue and
* the jobs in the Printer Queue.
*/
if (!GetJobs(hPrinter, &pJobs, &cJobs, &dwPrinterStatus))
return FALSE;
/*
* If the Printer reports an error, believe it.
*/
if (dwPrinterStatus &
(PRINTER_STATUS_ERROR |
PRINTER_STATUS_PAPER_JAM |
PRINTER_STATUS_PAPER_OUT |
PRINTER_STATUS_PAPER_PROBLEM |
PRINTER_STATUS_OUTPUT_BIN_FULL |
PRINTER_STATUS_NOT_AVAILABLE |
PRINTER_STATUS_NO_TONER |
PRINTER_STATUS_OUT_OF_MEMORY |
PRINTER_STATUS_OFFLINE |
PRINTER_STATUS_DOOR_OPEN)) {
free(pJobs);
return TRUE;
}
/*
* Find the Job in the Queue that is printing.
*/
for (i = 0; i < cJobs; i++) {
if (pJobs[i].Status & JOB_STATUS_PRINTING) {
/*
* If the job is in an error state,
* report an error for the printer.
* Code could be inserted here to
* attempt an interpretation of the
* pStatus member as well.
*/
if (pJobs[i].Status &
(JOB_STATUS_ERROR |
JOB_STATUS_OFFLINE |
JOB_STATUS_PAPEROUT |
JOB_STATUS_BLOCKED_DEVQ)) {
free(pJobs);
return TRUE;
}
}
}
/*
* No error condition.
*/
free(pJobs);
return FALSE;
}
I am trying to get the Bluetooth address of the local device using the Microsoft Bluetooth stack. I am targetting a Windows CE 6.0 device.
On MSDN I found the following code example :
SOCKADDR_BTH sab;
int len = sizeof(sab);
if (0 == getsockname (s, &sab, &len)) {
wprintf (L"Local Bluetooth device is %04x%08x, server channel = %d\n",
GET_NAP(sab.btAddr), GET_SAP(sab.btAddr), sab.port);
}
At : https://msdn.microsoft.com/en-us/library/ee495768(v=winembedded.60).aspx
In this example, s is not declared, so I assume its just a valid socket...
Here is the code I've written based on this example :
SOCKET s = socket( AF_BTH, SOCK_STREAM, BTHPROTO_RFCOMM );
if( s == INVALID_SOCKET )
{
return false;
}
SOCKADDR_BTH sab;
int len = sizeof( sab );
if( 0 == getsockname(s, (sockaddr *) & sab, & len ) )
{
// Use the BT address here
closesocket( s );
return true;
}
else
{
closesocket( s );
return false;
}
I had to cast the SOCKADDR_BTH * to a sockaddr * since the compiler wouldn't let me compile this, unlike what the example lets think.
This is getting me a 10022 error code indicating that I'm providing an invalid argument, which is not really surprising me due to this weird cast I had to do.
I Also tried another method involving the function BthReadLocalAddr which is documented on MSDN at : https://msdn.microsoft.com/en-us/library/ms887876.aspx
The function is indeed declared in Bt_api.h, but there is no Btdrt.lib in the CE 6.0 SDK. However there is a Btd.lib, but it doesn't seem to contain the definition of that function since I'm getting an unresolved external link error, which is not surprising.
How can I get this to work ? And maybe find a valid documentation about the MS bluetooth API that doesn't refer to files that do not exist ? Thank you.
I am learning SDL and I found this piece of code in the manual:
SDL_Rect **modes;
int i;
/* Get available fullscreen/hardware modes */
modes=SDL_ListModes(NULL, SDL_FULLSCREEN|SDL_HWSURFACE);
/* Check is there are any modes available */
if(modes == (SDL_Rect **)0){
printf("No modes available!\n");
exit(-1);
}
/* Check if or resolution is restricted */
if(modes == (SDL_Rect **)-1){
printf("All resolutions available.\n");
}
else{
/* Print valid modes */
printf("Available Modes\n");
for(i=0;modes[i];++i)
printf(" %d x %d\n", modes[i]->w, modes[i]->h);
}
I now that modes is a pointer to an array of SDL_rect but expression:
(modes== (SDL_Rect **)0)
escapes my reasoning.
What does (SDL_Rect **)0 means?
It's checking if it is a null pointer.
Since it's checking up if it's null, the cast it's not necessary, it could just be:
if(modes == 0)
or
if(modes)
I wrote a UNIX daemon (targeting Debian, but it shouldn't matter) and I wanted to provide some way of creating a ".pid" file, (a file which contains the process identifier of the daemon).
I searched for a way of opening a file only if it doesn't exist, but couldn't find one.
Basically, I could do something like:
if (fileexists())
{
//fail...
}
else
{
//create it with fopen() or similar
}
But as it stands, this code does not perform the task in a atomic fashion, and doing so would be dangerous, because another process might create the file during my test, and the file creation.
Do you guys have any idea on how to do that?
Thank you.
P.S: Bonus point for a solution which only involves std::streams.
man 2 open:
O_EXCL Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open()
will fail. The behavior of O_EXCL is undefined if O_CREAT is not specified.
so, you could call fd = open(name, O_CREAT | O_EXCL, 0644); /* Open() is atomic. (for a reason) */
UPDATE: and you should of course OR one of the O_RDONLY, O_WRONLY, or O_RDWR flags into the flags argument.
I learned about proper daemonizing here (back in the day):
http://www.enderunix.org/docs/eng/daemon.php
It is a good read. I have since improved the locking code to eliminate race conditions on platforms that allow advisory file locking with specific regions specified.
Here is a relevant snippet from a project that I was involved in:
static int zfsfuse_do_locking(int in_child)
{
/* Ignores errors since the directory might already exist */
mkdir(LOCKDIR, 0700);
if (!in_child)
{
ASSERT(lock_fd == -1);
/*
* before the fork, we create the file, truncating it, and locking the
* first byte
*/
lock_fd = creat(LOCKFILE, S_IRUSR | S_IWUSR);
if(lock_fd == -1)
return -1;
/*
* only if we /could/ lock all of the file,
* we shall lock just the first byte; this way
* we can let the daemon child process lock the
* remainder of the file after forking
*/
if (0==lockf(lock_fd, F_TEST, 0))
return lockf(lock_fd, F_TLOCK, 1);
else
return -1;
} else
{
ASSERT(lock_fd != -1);
/*
* after the fork, we instead try to lock only the region /after/ the
* first byte; the file /must/ already exist. Only in this way can we
* prevent races with locking before or after the daemonization
*/
lock_fd = open(LOCKFILE, O_WRONLY);
if(lock_fd == -1)
return -1;
ASSERT(-1 == lockf(lock_fd, F_TEST, 0)); /* assert that parent still has the lock on the first byte */
if (-1 == lseek(lock_fd, 1, SEEK_SET))
{
perror("lseek");
return -1;
}
return lockf(lock_fd, F_TLOCK, 0);
}
}
void do_daemon(const char *pidfile)
{
chdir("/");
if (pidfile) {
struct stat dummy;
if (0 == stat(pidfile, &dummy)) {
cmn_err(CE_WARN, "%s already exists; aborting.", pidfile);
exit(1);
}
}
/*
* info gleaned from the web, notably
* http://www.enderunix.org/docs/eng/daemon.php
*
* and
*
* http://sourceware.org/git/?p=glibc.git;a=blob;f=misc/daemon.c;h=7597ce9996d5fde1c4ba622e7881cf6e821a12b4;hb=HEAD
*/
{
int forkres, devnull;
if(getppid()==1)
return; /* already a daemon */
forkres=fork();
if (forkres<0)
{ /* fork error */
cmn_err(CE_WARN, "Cannot fork (%s)", strerror(errno));
exit(1);
}
if (forkres>0)
{
int i;
/* parent */
for (i=getdtablesize();i>=0;--i)
if ((lock_fd!=i) && (ioctl_fd!=i)) /* except for the lockfile and the comm socket */
close(i); /* close all descriptors */
/* allow for airtight lockfile semantics... */
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 200000; /* 0.2 seconds */
select(0, NULL, NULL, NULL, &tv);
VERIFY(0 == close(lock_fd));
lock_fd == -1;
exit(0);
}
/* child (daemon) continues */
setsid(); /* obtain a new process group */
VERIFY(0 == chdir("/")); /* change working directory */
umask(027); /* set newly created file permissions */
devnull=open("/dev/null",O_RDWR); /* handle standard I/O */
ASSERT(-1 != devnull);
dup2(devnull, 0); /* stdin */
dup2(devnull, 1); /* stdout */
dup2(devnull, 2); /* stderr */
if (devnull>2)
close(devnull);
/*
* contrary to recommendation, do _not_ ignore SIGCHLD:
* it will break exec-ing subprocesses, e.g. for kstat mount and
* (presumably) nfs sharing!
*
* this will lead to really bad performance too
*/
signal(SIGTSTP,SIG_IGN); /* ignore tty signals */
signal(SIGTTOU,SIG_IGN);
signal(SIGTTIN,SIG_IGN);
}
if (0 != zfsfuse_do_locking(1))
{
cmn_err(CE_WARN, "Unexpected locking conflict (%s: %s)", strerror(errno), LOCKFILE);
exit(1);
}
if (pidfile) {
FILE *f = fopen(pidfile, "w");
if (!f) {
cmn_err(CE_WARN, "Error opening %s.", pidfile);
exit(1);
}
if (fprintf(f, "%d\n", getpid()) < 0) {
unlink(pidfile);
exit(1);
}
if (fclose(f) != 0) {
unlink(pidfile);
exit(1);
}
}
}
See also http://gitweb.zfs-fuse.net/?p=sehe;a=blob;f=src/zfs-fuse/util.c;h=7c9816cc895db4f65b94592eebf96d05cd2c369a;hb=refs/heads/maint
The only way I can think of is to use system level locks. See this: C++ how to check if file is in use - multi-threaded multi-process system
One way to approach this problem is to open the file for appending. If the function succeeds and the position is at 0 then you can be fairly certain this is a new file. Could still be an empty file but that scenario may not be important.
FILE* pFile = fopen(theFilePath, "a+");
if (pFile && gfetpos(pFile) == 0) {
// Either file didn't previously exist or it did and was empty
} else if (pFile) {
fclose(pFile);
}
It would appear that there's no way to do it strictly using streams.
You can, instead, use open (as mentioned above by wildplasser) and if that succeeds, proceed to open the same file as a stream. Of course, if all you're writing to the file is a PID, it is unclear why you wouldn't just write it using C-style write().
O_EXCL only excludes other processes that are attempting to open the same file using O_EXCL. This, of course, means that you never have a perfect guarantee, but if the file name/location is somewhere nobody else is likely to be opening (other than folks you know are using O_EXCL) you should be OK.
I'm working with sqlite3 for the first time, and cannot get it to properly check a file before it opens it. So far, sqlite always returns OK on any file.
Also, the file name is a variable returned from the GTK file chooser. It returns an absolute path, I'm guessing this is not a problem.
Thanks for any help.
This is a snippet of the code:
int rc;
char *filename;
sqlite3 *db;
filename = gtk_file_chooser_get_filename(etc.);
if(SQLITE_OK == rc = sqlite3_open(filename,&db))
{ etc. }
sqlite3_open doesn't actually read the file until the first non-pragma statement is prepared.
sqlite3_open_v2 provides other options.
Does your code compile?
I believe this is an error
if (SQLITE_OK == rc = sqlite3_open(filename,&db)) { /* ... */ }
it's the same as
if ((SQLITE_OK == rc) = sqlite3_open(filename,&db)) { /* ... */ }
and you cannot assign something (the result of the sqlite3_open() call) to (SQLITE_OK == rc).
Try this:
if ((rc = sqlite3_open(filename,&db)) == SQLITE_OK) { /* ... */ }
/* or, if you really want the constant on the left side of the comparison */
if (SQLITE_OK == (rc = sqlite3_open(filename,&db))) { /* ... */ }