explain_vprintf(3)

💖 explain_vprintf — bestie, let's decode those errors 💖

okay so this is explain_vprintf(3), living in the Library Functions Manual (that's the section 3 girlies ✨), and it's literally the whole explain_vprintf crew whose entire job is telling you why your vprintf(3) call flopped. no cap.

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🌸 NAME 🌸

explain_vprintf — explain vprintf(3) errors 💅

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✨ SYNOPSIS ✨

#include <libexplain/vprintf.h>
const char *explain_vprintf(const char *format, va_list ap);
const char *explain_errno_vprintf(int errnum, const char *format,
va_list ap);
void explain_message_vprintf(char *message, int message_size, const char
*format, va_list ap);
void explain_message_errno_vprintf(char *message, int message_size, int
errnum, const char *format, va_list ap);

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🦋 DESCRIPTION 🦋

These functions are the ones you call when you wanna get actual explanations for errors handed back by the vprintf(3) system call. they're giving "translator for your cryptic errno" energy fr fr 🫶

💜 explain_vprintf

const char *explain_vprintf(const char *format, va_list ap);

the explain_vprintf function is how you obtain an explanation of an error returned by the vprintf(3) system call. the least the message will contain is the value of strerror(errno), but usually it does much better than that and tells you the underlying cause in way more detail. it's giving overachiever ✨

the errno global variable is the one that gets used to obtain the error value that's gonna be decoded.

• format — the original format, exactly as passed to the vprintf(3) system call. like, character for character, don't get cute with it.
• ap — the original ap, exactly as passed to the vprintf(3) system call.

Returns: the message explaining the error. heads up bestie, this message buffer is shared by all libexplain functions that don't supply a buffer in their argument list. so it's gonna get overwritten by the next call to any libexplain function that shares this buffer — including calls from other threads. 😭

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

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

errno = EINVAL;
int result = vprintf(format, ap);
if (result < 0)
{
    fprintf(stderr, "%s\n", explain_vprintf(format, ap));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_vprintf_or_die(3) function. obsessed, honestly. 👑

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🎀 explain_errno_vprintf

const char *explain_errno_vprintf(int errnum, const char *format,
va_list ap);

the explain_errno_vprintf function is used to obtain an explanation of an error returned by the vprintf(3) 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.

• errnum — the error value to be decoded, usually grabbed from the errno global variable right before this function is called. you need to do this if you have to call any code between the system call you're explaining and this function, because so many libc functions will go and alter the value of errno on you. sneaky. 🙈
• format — the original format, exactly as passed to the vprintf(3) system call.
• ap — the original ap, exactly as passed to the vprintf(3) 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:

errno = EINVAL;
int result = vprintf(format, ap);
if (result < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_vprintf(err, format,
    ap));
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_vprintf_or_die(3) function. slay. 🌈

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🧚 explain_message_vprintf

void explain_message_vprintf(char *message, int message_size, const char
*format, va_list ap);

the explain_message_vprintf function is used to obtain an explanation of an error returned by the vprintf(3) 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.

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. character development honestly 🫶
• message_size — the size in bytes of the location in which to store the returned message.
• format — the original format, exactly as passed to the vprintf(3) system call.
• ap — the original ap, exactly as passed to the vprintf(3) system call.

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

errno = EINVAL;
int result = vprintf(format, ap);
if (result < 0)
{
    char message[3000];
    explain_message_vprintf(message, sizeof(message), format,
    ap);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_vprintf_or_die(3) function. ✨

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💅 explain_message_errno_vprintf

void explain_message_errno_vprintf(char *message, int message_size, int
errnum, const char *format, va_list ap);

the explain_message_errno_vprintf function is used to obtain an explanation of an error returned by the vprintf(3) 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.

• 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.
• format — the original format, exactly as passed to the vprintf(3) system call.
• ap — the original ap, exactly as passed to the vprintf(3) system call.

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

errno = EINVAL;
int result = vprintf(format, ap);
if (result < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_vprintf(message, sizeof(message), err,
    format, ap);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the above code example is available pre‐packaged as the explain_vprintf_or_die(3) function. iconic behavior. 👑

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🔥 SEE ALSO 🔥

• vprintf(3) — formatted output conversion
• explain_vprintf_or_die(3) — formatted output conversion and report errors

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👑 COPYRIGHT 👑

libexplain version 1.4 Copyright (C) 2010 Peter Miller

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and that's the whole page bestie, you ate that 💖

this little manual page came from libexplain version 1.4, with the copyright held by Peter Miller, 2010 — and the page itself is filed under explain_vprintf(3) in the Library Functions Manual. go forth and decode your errnos, queen. 🎀✨🦋