explain_writev(3)

💖 explain_writev(3) 💖

okay bestie, sit down, hydrate, because we're about to talk about error messages that actually slap. this is a page from the Library Functions Manual (manual section 3, the library-call girlies), and it's all about the explain_writev family of functions. yes, the whole fam. 💅

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✨ NAME ✨

explain_writev — explain writev(2) errors 🫶

like, it explains why your writev(2) call said no. that's the whole job. iconic.

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🌸 SYNOPSIS 🌸

#include <libexplain/writev.h>
const char *explain_writev(int fildes, const struct iovec *data, int
data_size);
const char *explain_errno_writev(int errnum, int fildes, const struct
iovec *data, int data_size);
void explain_message_writev(char *message, int message_size, int fildes,
const struct iovec *data, int data_size);
void explain_message_errno_writev(char *message, int message_size, int
errnum, int fildes, const struct iovec *data, int data_size);

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🦋 DESCRIPTION 🦋

so these functions exist so you can get explanations for errors returned by the writev(2) system call. not vibes-based guesses — actual explanations. main character energy for your error handling. 👑

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🎀 explain_writev 🎀

const char *explain_writev(int fildes, const struct iovec *data, int
data_size);

the explain_writev function gets you an explanation of an error returned by the writev(2) system call. the least the message will contain is the value of strerror(errno), but usually it does so much better and points at the underlying cause in more detail. lowkey a glow-up over plain strerror.

the errno global variable is what it uses to obtain the error value to be decoded. fr fr.

• fildes — the original fildes, exactly as passed to the writev(2) system call. no edits, no remix, the original.
• data — the original data, exactly as passed to the writev(2) system call.
• data_size — the original data_size, exactly as passed to the writev(2) system call.

Returns:

the message explaining the error. ⭐ this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. it will be overwritten by the next call to any libexplain function which shares this buffer — including other threads. so like. don't get attached to it, bestie. 😭

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library. periodt.

Example: this function is intended to be used in a fashion similar to the following example:

ssize_t result = writev(fildes, data, data_size);
if (result < 0)
{
    fprintf(stderr, "%s\n", explain_writev(fildes, data,
    data_size));
    exit(EXIT_FAILURE);
}

the above code example is available pre-packaged as the explain_writev_or_die(3) function. no cap. 🧚

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💜 explain_errno_writev 💜

const char *explain_errno_writev(int errnum, int fildes, const struct
iovec *data, int data_size);

the explain_errno_writev function gets you an explanation of an error returned by the writev(2) system call. the least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail. same energy, but you're handing it the error yourself.

• errnum — the error value to be decoded, usually obtained from the errno global variable just before this function is called. this is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno. so like, grab it early or it's gone. 💀
• fildes — the original fildes, exactly as passed to the writev(2) system call.
• data — the original data, exactly as passed to the writev(2) system call.
• data_size — the original data_size, exactly as passed to the writev(2) system call.

Returns:

the message explaining the error. this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. this will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. 🫶

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library.

Example: this function is intended to be used in a fashion similar to the following example:

ssize_t result = writev(fildes, data, data_size);
if (result < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_writev(err, fildes,
    data, data_size));
    exit(EXIT_FAILURE);
}

the above code example is available pre-packaged as the explain_writev_or_die(3) function. 💅

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🌈 explain_message_writev 🌈

void explain_message_writev(char *message, int message_size, int fildes,
const struct iovec *data, int data_size);

the explain_message_writev function gets you an explanation of an error returned by the writev(2) system call. the least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail. and this one lets you bring the buffer, which is kind of a serve. 💖

the errno global variable will be used to obtain the error value to be decoded.

• message — the location in which to store the returned message. if a suitable message return buffer is supplied, this function is thread safe. look at her go. ✨
• message_size — the size in bytes of the location in which to store the returned message.
• fildes — the original fildes, exactly as passed to the writev(2) system call.
• data — the original data, exactly as passed to the writev(2) system call.
• data_size — the original data_size, exactly as passed to the writev(2) system call.

Example: this function is intended to be used in a fashion similar to the following example:

ssize_t result = writev(fildes, data, data_size);
if (result < 0)
{
    char message[3000];
    explain_message_writev(message, sizeof(message), fildes,
    data, data_size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre-packaged as the explain_writev_or_die(3) function. 🍓

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👑 explain_message_errno_writev 👑

void explain_message_errno_writev(char *message, int message_size, int
errnum, int fildes, const struct iovec *data, int data_size);

the explain_message_errno_writev function gets you an explanation of an error returned by the writev(2) system call. the least the message will contain is the value of strerror(errno), but usually it will do much better, and indicate the underlying cause in more detail. it's the buffer-plus-errnum combo and honestly? ate. 🔥

• message — the location in which to store the returned message. if a suitable message return buffer is supplied, this function is thread safe.
• message_size — the size in bytes of the location in which to store the returned message.
• errnum — the error value to be decoded, usually obtained from the errno global variable just before this function is called. this is necessary if you need to call any code between the system call to be explained and this function, because many libc functions will alter the value of errno.
• fildes — the original fildes, exactly as passed to the writev(2) system call.
• data — the original data, exactly as passed to the writev(2) system call.
• data_size — the original data_size, exactly as passed to the writev(2) system call.

Example: this function is intended to be used in a fashion similar to the following example:

ssize_t result = writev(fildes, data, data_size);
if (result < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_writev(message, sizeof(message), err,
    fildes, data, data_size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre-packaged as the explain_writev_or_die(3) function. 🧚💫

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💫 SEE ALSO 💫

• writev(2) — write data from multiple buffers
• explain_writev_or_die(3) — write data from multiple buffers and report errors

go read those too, bestie, they're the supporting cast and they understood the assignment. 🫶

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📜 COPYRIGHT 📜

libexplain version 1.4 Copyright (C) 2009 Peter Miller

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okay that's the whole page, you made it, I'm so proud of you 💖✨ this was explain_writev(3) from the Library Functions Manual, and if you ever need her again she lives right there in section 3 with all her sisters. go forth and explain your errors, queen. 💅🎀🦋