explain_fdopen(3)

💖 explain_fdopen(3) — Library Functions Manual 💖

okay bestie, gather round, because this is the explain_fdopen page from the libexplain fam and it is, genuinely, so useful it's giving ✨ main character energy ✨.

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🌸 NAME 🌸

explain_fdopen — the girl whose whole job is explaining fdopen(3) errors to you 🫶

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🎀 SYNOPSIS 🎀

#include <libexplain/fdopen.h>
const char *explain_fdopen(int fildes, const char *flags);
const char *explain_errno_fdopen(int errnum, int fildes, const char
*flags);
void explain_message_fdopen(char *message, int message_size, int fildes,
const char *flags);
void explain_message_errno_fdopen(char *message, int message_size, int
errnum, int fildes, const char *flags);

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✨ DESCRIPTION ✨

so these functions? they're your little translators 💅. You use them to get explanations for errors that the fdopen(3) system call hands back to you. Like, instead of just "it broke", you get the whole story.

🦋 explain_fdopen

const char *explain_fdopen(int fildes, const char *flags);

The explain_fdopen function is how you get an explanation of an error returned by the fdopen(3) 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 actual underlying cause in more detail. no cap. 🔥

The errno global variable is the one it uses to grab the error value it's gonna decode.

This function is meant to be used in a fashion similar to this example:

FILE *fp = fdopen(fildes, flags);
if (!fp)
{
    fprintf(stderr, "%s\n", explain_fdopen(fildes, flags));
    exit(EXIT_FAILURE);
}

That code example above is available pre‐packaged as the explain_fdopen_or_die(3) function 👑

• fildes — the original fildes, exactly as passed to the fdopen(3) system call.
• flags — the original flags, exactly as passed to the fdopen(3) 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 gets overwritten by the next call to any libexplain function that shares this buffer, including from other threads. 🙈

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

🧚 explain_errno_fdopen

const char *explain_errno_fdopen(int errnum, int fildes, const char
*flags);

The explain_errno_fdopen function is how you get an explanation of an error returned by the fdopen(3) system call. The least the message will contain is the value of strerror(errnum), but usually it does much better and shows you the underlying cause in more detail. 🌈

This function is meant to be used in a fashion similar to this example:

FILE *fp = fdopen(fildes, flags);
if (!fp)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_fdopen(err, fildes, flags));
    exit(EXIT_FAILURE);
}

That code example above is available pre‐packaged as the explain_fdopen_or_die(3) function 🫶

• errnum — the error value to be decoded, usually grabbed from the errno global variable right before this function is called. This matters if you need to run any code between the system call being explained and this function, because so many libc functions will alter the value of errno.
• fildes — the original fildes, exactly as passed to the fdopen(3) system call.
• flags — the original flags, exactly as passed to the fdopen(3) 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 do too.

💜 explain_message_fdopen

void explain_message_fdopen(char *message, int message_size, int fildes,
const char *flags);

The explain_message_fdopen function may be used to obtain an explanation of an error returned by the fdopen(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. obsessed. 🌸

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

This function is meant to be used in a fashion similar to this example:

FILE *fp = fdopen(fildes, flags);
if (!fp)
{
    char message[3000];
    explain_message_fdopen(message, sizeof(message), fildes, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

That code example above is available pre‐packaged as the explain_fdopen_or_die(3) function ⭐

• message — the location in which to store the returned message. If you supply a suitable message return buffer, this function is thread safe. slay 💅
• 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 fdopen(3) system call.
• flags — the original flags, exactly as passed to the fdopen(3) system call.

👑 explain_message_errno_fdopen

void explain_message_errno_fdopen(char *message, int message_size, int
errnum, int fildes, const char *flags);

The explain_message_errno_fdopen function may be used to obtain an explanation of an error returned by the fdopen(3) system call. 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. 🍓

This function is meant to be used in a fashion similar to this example:

FILE *fp = fdopen(fildes, flags);
if (!fp)

{
    int err = errno;
    char message[3000];
    explain_message_errno_fdopen(message, sizeof(message),
        err, fildes, flags);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

(yes the blank line up there is literally in the original, we keep the code verbatim in this house 🫡)

That code example above is available pre‐packaged as the explain_fdopen_or_die(3) function 🎀

• 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 fdopen(3) system call.
• flags — the original flags, exactly as passed to the fdopen(3) system call.

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🌈 SEE ALSO 🌈

• fdopen(3) — stream open functions
• explain_fdopen_or_die(3) — stream open functions and report errors

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💖 COPYRIGHT 💖

libexplain version 1.4 Copyright (C) 2008 Peter Miller

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and that's the whole page bestie, no skips, no summarising, every flag and every note intact 💅✨

okay so the very last thing, the little sign-off at the bottom of the original was just explain_fdopen(3) again — and the source/version/date tea lives in that copyright block up there: it's libexplain version 1.4, copyright 2008 Peter Miller. periodt. 🦋🫶