READV(3POSIX)

💖 readv(3POSIX) — POSIX Programmer's Manual 💖

okay bestie so this page is readv(3POSIX), and it lives in the POSIX Programmer's Manual — like, the IEEE/The Open Group 2017 era of things. She's a classic. Come sit with me. 🫶

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🌸 PROLOG 🌸

Real talk before we even start: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so if you're on Linux, go check the corresponding Linux manual page for the actual tea on Linux behavior), or honestly the interface might just not be implemented on Linux at all. Vibe check your platform first, bestie. 💅

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✨ NAME ✨

readv — read a vector. that's it. that's the name. iconic behavior.

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🦋 SYNOPSIS 🦋

#include <sys/uio.h>

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

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💜 DESCRIPTION 💜

So the readv() function shall be equivalent to read(), except for the stuff listed below. That's the whole bit — it's read() but make it vector. 🎀

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 it's 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. And here's the part that matters: the readv() function shall always fill an area completely before proceeding to the next. No half-filling one buffer and skipping ahead, she's not messy like that. 🧚

Upon successful completion, readv() shall mark for update the last data access timestamp of the file. Yes bestie, she's updating your timestamps. That's just what she does. ⭐

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🔥 RETURN VALUE 🔥

Refer to read(). That's it, that's the whole section. She's not repeating herself. 👑

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💀 ERRORS 💀

Refer to read().

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

• EINVAL — the sum of the iov_len values in the iov array overflowed an ssize_t. like, too much. overflowing. not the vibe.

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. (translation: the juicy technical stuff is done, everything below is ✨bonus content✨)

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🌈 EXAMPLES 🌈

🌸 Reading Data into an Array 🌸

This example reads data from the file associated with the file descriptor fd into the buffers specified by members of the iov array. Watch and learn, bestie:

#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);
...

three buffers, one call, zero stress. slay. 💅✨

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🎀 APPLICATION USAGE 🎀

None. she said no notes. 🙈

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💖 RATIONALE 💖

Refer to read(). (she's keeping it short and mysterious, we respect it.)

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⭐ FUTURE DIRECTIONS ⭐

None.

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👑 SEE ALSO 👑

• read()
• writev()

The Base Definitions volume of POSIX.1‐2017, <sys_uio.h>

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📜 COPYRIGHT 📜

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie!! 💖 this one's brought to you by IEEE/The Open Group, dated 2017 — go forth and read your vectors, no cap. 🦋✨