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   writev.3p    ( 3 )

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Пролог (Prolog)

This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

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Имя (Name)

writev — write a vector

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Синопсис (Synopsis)

#include <sys/uio.h>

       ssize_t writev(int fildes, const struct iovec *iov, int iovcnt);

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Описание (Description)

The writev() function shall be equivalent to write(), except as
       described below. The writev() function shall gather output data
       from the iovcnt buffers specified by the members of the iov
       array: iov[0], iov[1], ..., iov[iovcnt-1].  The iovcnt argument
       is valid if greater than 0 and less than or equal to {IOV_MAX},
       as defined in <limits.h>.

       Each iovec entry specifies the base address and length of an area
       in memory from which data should be written. The writev()
       function shall always write a complete area before proceeding to
       the next.

       If fildes refers to a regular file and all of the iov_len members
       in the array pointed to by iov are 0, writev() shall return 0 and
       have no other effect. For other file types, the behavior is
       unspecified.

       If the sum of the iov_len values is greater than {SSIZE_MAX}, the
       operation shall fail and no data shall be transferred.

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Возвращаемое значение (Return value)

Upon successful completion, writev() shall return the number of
       bytes actually written. Otherwise, it shall return a value of -1,
       the file-pointer shall remain unchanged, and errno shall be set
       to indicate an error.

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Ошибки (Error)

Refer to write(3p).

       In addition, the writev() function shall fail if:

       EINVAL The sum of the iov_len values in the iov array would
              overflow an ssize_t.

       The writev() function may fail and set errno to:

       EINVAL The iovcnt argument was less than or equal to 0, or
              greater than {IOV_MAX}.

       The following sections are informative.

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Примеры (Examples)

Writing Data from an Array
       The following example writes data from the buffers specified by
       members of the iov array to the file associated with the file
       descriptor fd.

           #include <sys/types.h>
           #include <sys/uio.h>
           #include <unistd.h>
           ...
           ssize_t bytes_written;
           int fd;
           char *buf0 = "short string\n";
           char *buf1 = "This is a longer string\n";
           char *buf2 = "This is the longest string in this example\n";
           int iovcnt;
           struct iovec iov[3];

           iov[0].iov_base = buf0;
           iov[0].iov_len = strlen(buf0);
           iov[1].iov_base = buf1;
           iov[1].iov_len = strlen(buf1);
           iov[2].iov_base = buf2;
           iov[2].iov_len = strlen(buf2);
           ...
           iovcnt = sizeof(iov) / sizeof(struct iovec);

           bytes_written = writev(fd, iov, iovcnt);
           ...

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Использование в приложениях (Application usage)

None.

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Обоснование (Rationale)

Refer to write(3p).

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Будущие направления (Future directions)

None.

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Смотри также (See also)

readv(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2017, limits.h(0p),
       sys_uio.h(0p)

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