explain_lseek(3)

💖 explain_lseek — the manual, but make it make sense 💖

okay bestie, gather round, because today we're decoding explain_lseek(3) from the Library Functions Manual and honestly? it's giving "your syscall ghosted you and left no note." this whole page is about getting a human-readable explanation of what went wrong in an lseek(2) call. no cap. 🦋

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✨ NAME ✨

explain_lseek — explain lseek(2) errors 👑

🌸 SYNOPSIS 🌸

#include <libexplain/lseek.h>
const char *explain_lseek(int fildes, long long offset, int whence);
const char *explain_errno_lseek(int errnum, int fildes, long long offset, int whence);
void explain_message_lseek(char *message, int message_size, int fildes, long long offset, int whence);
void explain_message_errno_lseek(char *message, int message_size, int errnum, int fildes, long long offset, int whence);

four functions, one mission: tell you why your lseek(2) flopped. 💅

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💜 DESCRIPTION 💜

so like, these functions exist so you can pull out explanations for lseek(2) errors. they're your little error-decoding besties. 🫶

🎀 explain_lseek

const char *explain_lseek(int fildes, long long offset, int whence);

explain_lseek is the one you call when you want a human readable explanation of what went wrong in an lseek(2) system call. the least it will give you is the value of strerror(errno), but usually it does so much better and points at the underlying cause in way more detail. lowkey overachiever behavior and we love that. ✨

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

it's meant to be used in a fashion similar to this example:

if (lseek(fd, offset, whence) == (off_t)-1)
{
    fprintf(stderr, '%s0, explain_lseek(fd, offset, whence);
    exit(EXIT_FAILURE);
}

• fildes — the original fildes, exactly as passed to the lseek(2) system call.
• offset — the original offset, exactly as passed to the lseek(2) system call.
• whence — the original whence, exactly as passed to the lseek(2) system call.

Returns:

the message explaining the error. ⚠️ this message buffer is shared by all libexplain functions that don't supply a buffer in their argument list. it will be overwritten by the next call to any libexplain function that shares this buffer — including calls from other threads. yes, it's that kind of situationship. 😭

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

🌈 explain_errno_lseek

const char *explain_errno_lseek(int errnum, int fildes, long long offset, int whence);

explain_errno_lseek does the same job — human readable explanation of what went wrong in an lseek(2) system call. the least the message will contain is the value of strerror(errnum), but usually it goes way harder and indicates the underlying cause in more detail. 💅

used in a fashion similar to this:

if (lseek(fd, offset, whence) == (off_t)-1)
{
    int errnum = errno;
    fprintf(stderr, '%s0, explain_errno_lseek(fd, eernum, offset,
        whence);
    exit(EXIT_FAILURE);
}

• 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, bestie, it will not wait for you. 🙈
• fildes — the original fildes, exactly as passed to the lseek(2) system call.
• offset — the original offset, exactly as passed to the lseek(2) system call.
• whence — the original whence, exactly as passed to the lseek(2) system call.

Returns:

the message explaining the error. ⚠️ this message buffer is shared by all libexplain functions that don't supply a buffer in their argument list. it will be overwritten by the next call to any libexplain function that 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.

🦋 explain_message_lseek

void explain_message_lseek(char *message, int message_size, int fildes, long long offset, int whence);

explain_message_lseek — you guessed it — gets you a human readable explanation of what went wrong in an lseek(2) system call. the least the message will contain is the value of strerror(errno), but usually it does much better and indicates the underlying cause in more detail. iconic. ✨

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

use it in a fashion similar to this:

if (lseek(fd, offset, whence) == (off_t)-1)
{
    char message[3000];
    explain_message_lseek(message, sizeof(message), fd, offset, whence);
    fprintf(stderr, '%s0, message);
    exit(EXIT_FAILURE);
}

• message — the location in which to store the returned message. because a message return buffer has been supplied, this function is thread safe. 👑 (yes ma'am, you brought your own buffer, you get thread safety, main character energy fr fr)
• 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 lseek(2) system call.
• offset — the original offset, exactly as passed to the lseek(2) system call.
• whence — the original whence, exactly as passed to the lseek(2) system call.

🧚 explain_message_errno_lseek

void explain_message_errno_lseek(char *message, int message_size, int errnum, int fildes, long long offset, int whence);

explain_message_errno_lseek — human readable explanation of what went wrong in an lseek(2) system call, same deal. the least the message will contain is the value of strerror(errnum), but usually it will do much better and indicate the underlying cause in more detail. 🫶

the vibe, as an example:

if (lseek(fd, offset, whence) == (off_t)-1)
{
    char message[3000];
    int errnum = errno;
    explain_message_errno_lseek(message, sizeof(message), errnum, fd,
        offset, whence);
    fprintf(stderr, '%s0, message);
    exit(EXIT_FAILURE);
}

• message — the location in which to store the returned message. because a message return buffer has been 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 lseek(2) system call.
• offset — the original offset, exactly as passed to the lseek(2) system call.
• whence — the original whence, exactly as passed to the lseek(2) system call.

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🌟 COPYRIGHT 🌟

libexplain version 1.4 Copyright (C) 2008 Peter Miller

💌 AUTHOR 💌

Written by Peter Miller <pmiller@opensource.org.au>

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and that's the whole page, bestie!! 🎀 this was explain_lseek(3) from libexplain version 1.4, copyright © 2008 Peter Miller, authored by Peter Miller <pmiller@opensource.org.au> — go forth and decode your errnos, you absolute legend. mwah. 💖💅✨