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   sockatmark    ( 3 )

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Имя (Name)

sockatmark - determine whether socket is at out-of-band mark

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Синопсис (Synopsis)

#include <sys/socket.h>

       int sockatmark(int sockfd);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       sockatmark():
           _POSIX_C_SOURCE >= 200112L

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Описание (Description)

sockatmark() returns a value indicating whether or not the socket
       referred to by the file descriptor sockfd is at the out-of-band
       mark.  If the socket is at the mark, then 1 is returned; if the
       socket is not at the mark, 0 is returned.  This function does not
       remove the out-of-band mark.

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Возвращаемое значение (Return value)

A successful call to sockatmark() returns 1 if the socket is at
       the out-of-band mark, or 0 if it is not.  On error, -1 is
       returned and errno is set to indicate the error.

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Ошибки (Error)

EBADF  sockfd is not a valid file descriptor.

       EINVAL sockfd is not a file descriptor to which sockatmark() can
              be applied.

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Версии (Versions)

sockatmark() was added to glibc in version 2.2.4.

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Атрибуты (Attributes)

For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │sockatmark()                          │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

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Стандарты (Conforming to)

POSIX.1-2001, POSIX.1-2008.

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Примечание (Note)

If sockatmark() returns 1, then the out-of-band data can be read
       using the MSG_OOB flag of recv(2).

       Out-of-band data is supported only on some stream socket
       protocols.

       sockatmark() can safely be called from a handler for the SIGURG
       signal.

       sockatmark() is implemented using the SIOCATMARK ioctl(2)
       operation.

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Ошибки (баги) (Bugs)

Prior to glibc 2.4, sockatmark() did not work.

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Примеры (Examples)

The following code can be used after receipt of a SIGURG signal
       to read (and discard) all data up to the mark, and then read the
       byte of data at the mark:

           char buf[BUF_LEN];
           char oobdata;
           int atmark, s;

           for (;;) {
               atmark = sockatmark(sockfd);
               if (atmark == -1) {
                   perror("sockatmark");
                   break;
               }

               if (atmark)
                   break;

               s = read(sockfd, buf, BUF_LEN);
               if (s == -1)
                   perror("read");
               if (s <= 0)
                   break;
           }

           if (atmark == 1) {
               if (recv(sockfd, &oobdata, 1, MSG_OOB) == -1) {
                   perror("recv");
                   ...
               }
           }

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Смотри также (See also)

fcntl(2), recv(2), send(2), tcp(7)

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