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   readv.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)

readv — read a vector

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Синопсис (Synopsis)

#include <sys/uio.h>

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

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Описание (Description)

The readv() function shall be equivalent to read(), except as
       described below. The readv() function shall place the input data
       into 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}.

       Each iovec entry specifies the base address and length of an area
       in memory where data should be placed. The readv() function shall
       always fill an area completely before proceeding to the next.

       Upon successful completion, readv() shall mark for update the
       last data access timestamp of the file.

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Возвращаемое значение (Return value)

Refer to read(3p).

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Ошибки (Error)

Refer to read(3p).

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

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

       The readv() function may fail if:

       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)

Reading Data into an Array
       The following example reads data from the file associated with
       the file descriptor fd into the buffers specified by members of
       the iov array.

           #include <sys/types.h>
           #include <sys/uio.h>
           #include <unistd.h>
           ...
           ssize_t bytes_read;
           int fd;
           char buf0[20];
           char buf1[30];
           char buf2[40];
           int iovcnt;
           struct iovec iov[3];

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

           bytes_read = readv(fd, iov, iovcnt);
           ...

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Использование в приложениях (Application usage)

None.

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Обоснование (Rationale)

Refer to read(3p).

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Будущие направления (Future directions)

None.

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Смотри также (See also)

read(3p), writev(3p)

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

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