explain_printf(3)

💖 explain_printf — bestie, let's decode ur printf(3) errors 💖

okay so this is explain_printf(3), and it lives in the Library Functions Manual. It's part of libexplain, and it's literally the friend who shows up when printf(3) is being dramatic and you're like "what does this error even MEAN 😭".

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✨ NAME ✨

explain_printf — it explains printf(3) errors. that's the whole job. no cap. 🫶

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✨ SYNOPSIS ✨

#include <libexplain/printf.h>
const char *explain_printf(const char *format);
const char *explain_errno_printf(int errnum, const char *format);
void explain_message_printf(char *message, int message_size, const char
*format);
void explain_message_errno_printf(char *message, int message_size, int
errnum, const char *format);

look at those four icons. four whole functions. we're gonna go through each one, one at a time, like a get-ready-with-me but for error messages 💅

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✨ DESCRIPTION ✨

these functions are ur little translators. you use them to get explanations for errors that come back from the printf(3) system call. like, the call failed, and instead of just staring at a number you get an actual sentence about it.

the bare minimum any of these will give you is the value of strerror(errno). but usually they do so much better and point at the actual underlying cause with way more detail. it's giving detective energy 🔍

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🌸 explain_printf 🌸

const char *explain_printf(const char *format);

explain_printf is the one you call to get an explanation of an error returned by the printf(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.

it grabs the error value to decode from the errno global variable.

• format — the original format, exactly as passed to the printf(3) system call. like, exactly exactly. don't go editing it, bestie.

Returns:

the message explaining the error. ⚠️ heads up: this message buffer is shared by all libexplain functions which don't supply a buffer in their argument list. so the next call to any libexplain function that shares this buffer will overwrite it — including calls from other threads. it's a communal water bottle, no one owns it 🚰

Note: this function is not thread safe, because it shares a return buffer across all threads, and many other functions in this library do the same. so if you're multithreaded, be careful, okay? 🫶

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

errno = 0;
int result = printf(format);
if (result < 0 && errno != 0)
{
    fprintf(stderr, "%s\n", explain_printf(format));
    exit(EXIT_FAILURE);
}

and the tea ☕ — the above code example is available pre-packaged as the explain_printf_or_die(3) function. so if you don't wanna write it urself, it's already there for u.

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🌸 explain_errno_printf 🌸

const char *explain_errno_printf(int errnum, const char *format);

explain_errno_printf is used to obtain an explanation of an error returned by the printf(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 just before this function is called. this matters if you need to run any code between the system call you're explaining and this function, because many libc functions will alter the value of errno. so snapshot it early or it's gone, fr fr.
• format — the original format, exactly as passed to the printf(3) system call.

Returns:

the message explaining the error. ⚠️ same situation as before: this message buffer is shared by all libexplain functions which don't supply a buffer in their argument list, and it will be overwritten by the next call to any libexplain function that shares this buffer, including from other threads.

Note: not thread safe. shares a return buffer across all threads, and many other functions in this library do too. iconic behaviour, but risky 💀

Example: intended to be used in a fashion similar to:

errno = 0;
int result = printf(format);
if (result < 0 && errno != 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_printf(err, format));
    exit(EXIT_FAILURE);
}

and yes bestie, the above code example is available pre-packaged as the explain_printf_or_die(3) function.

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🌸 explain_message_printf 🌸

void explain_message_printf(char *message, int message_size, const char
*format);

explain_message_printf is used to obtain an explanation of an error returned by the printf(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.

it uses the errno global variable to get the error value to be decoded.

• message — the location in which to store the returned message. 👑 and here's the glow-up: if a suitable message return buffer is supplied, this function is thread safe. ur own buffer, ur own rules.
• message_size — the size in bytes of the location in which to store the returned message. keep it accurate pls.
• format — the original format, exactly as passed to the printf(3) system call.

Example: intended to be used in a fashion similar to:

errno = 0;
int result = printf(format);
if (result < 0 && errno != 0)
{
    char message[3000];
    explain_message_printf(message, sizeof(message), format);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

and the above code example is available pre-packaged as the explain_printf_or_die(3) function. 🎀

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🌸 explain_message_errno_printf 🌸

void explain_message_errno_printf(char *message, int message_size, int
errnum, const char *format);

explain_message_errno_printf is used to obtain an explanation of an error returned by the printf(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. ✨ and again: if a suitable message return buffer is supplied, this function is thread safe. main character energy, truly.
• 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. grab it before it changes, i'm begging 😭
• format — the original format, exactly as passed to the printf(3) system call.

Example: intended to be used in a fashion similar to:

errno = 0;
int result = printf(format);
if (result < 0 && errno != 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_printf(message, sizeof(message), err,
    format);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

and (say it with me) the above code example is available pre-packaged as the explain_printf_or_die(3) function. 🦋

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✨ SEE ALSO ✨

• printf(3) — formatted output conversion
• explain_printf_or_die(3) — formatted output conversion and report errors

go read those too, bestie, they're the whole ecosystem 💜

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✨ COPYRIGHT ✨

libexplain version 1.4 Copyright (C) 2010 Peter Miller

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and that's the whole page, babes 🫶 this was explain_printf(3) from the Library Functions Manual, brought to you by libexplain version 1.4, Copyright (C) 2010 Peter Miller. stay safe, snapshot ur errno, and don't share buffers unless you mean it. mwah 💅✨🌈