explain_execvp(3)

💖 NAME 💖

explain_execvp — bestie, it explains your execvp(3) errors 💅

okay so real talk: this whole page lives in the Library Functions Manual, and it's the explain_execvp(3) glow-up guide. it's giving "my syscall failed and I need to know why" energy, and honestly? iconic. 🫶

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✨ SYNOPSIS ✨

#include <libexplain/execvp.h>
const char *explain_execvp(const char *pathname, char *const *argv);
const char *explain_errno_execvp(int errnum, const char *pathname, char *const *argv);
void explain_message_execvp(char *message, int message_size, const char *pathname, char *const *argv);
void explain_message_errno_execvp(char *message, int message_size, int errnum, const char *pathname, char *const *argv);

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🌸 DESCRIPTION 🌸

so these functions are your little support system 💜 — you use them to get explanations for errors that the execvp(3) system call hands back to you. no cap, they're here to translate "it broke" into "here's literally what happened."

🎀 explain_execvp 🎀

const char *explain_execvp(const char *pathname, char *const *argv);

the explain_execvp function gets you an explanation of an error that came back from the execvp(3) system call. the least the message will contain is the value of strerror(errno), but usually it does way better than that and points at the actual underlying cause in more detail. main character energy, honestly. ✨

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

you're meant to use this function in a fashion similar to this example:

if (execvp(pathname, argv) < 0)
{
    fprintf(stderr, "%s\n", explain_execvp(pathname, argv));
    exit(EXIT_FAILURE);
}

that code example above? it's available pre‐packaged as the explain_execvp_or_die(3) function. convenient queen 🎀

• pathname — the original pathname, exactly as passed to the execvp(3) system call. no edits, no vibes-based rewriting.
• argv — the original argv, exactly as passed to the execvp(3) system call.

Returns: the message explaining the error. heads up though — 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 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.

🦋 explain_errno_execvp 🦋

const char *explain_errno_execvp(int errnum, const char *pathname, char *const *argv);

the explain_errno_execvp function gets you an explanation of an error returned by the execvp(3) system call. the least the message will contain is the value of strerror(errnum), but usually it does much better and names the underlying cause in more detail. 💖

you're meant to use this one in a fashion similar to this:

if (execvp(pathname, argv) < 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_execvp(err,
        pathname, argv));
    exit(EXIT_FAILURE);
}

and yep, that code example is available pre‐packaged as the explain_execvp_or_die(3) function.

• errnum — the error value to be decoded, usually grabbed from the global variable errno 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 mess with the value of errno. 🙈
• pathname — the original pathname, exactly as passed to the execvp(3) system call.
• argv — the original argv, exactly as passed to the execvp(3) system call.

Returns: the message explaining the error. same situation as before — this message buffer is shared by all libexplain functions that don't supply a buffer in their argument list. it'll be overwritten by the next call to any libexplain function sharing this buffer, other threads included.

Note: not thread safe, because it shares a return buffer across all threads, and lots of other functions in this library do the same thing.

🌈 explain_message_execvp 🌈

void explain_message_execvp(char *message, int message_size, const char *pathname, char *const *argv);

the explain_message_execvp function may be used to obtain an explanation of an error returned by the execvp(3) system call. the least the message will contain is the value of strerror(errno), but usually it goes way harder and points out the underlying cause in more detail. 🔥

it uses the global variable errno to get the error value to decode.

you'd use it in a fashion similar to this:

if (execvp(pathname, argv) < 0)
{
    char message[3000];
    explain_message_execvp(message, sizeof(message), pathname, argv);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

and yes bestie, that code example is available pre‐packaged as the explain_execvp_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. 👑
• message_size — the size in bytes of the location in which to store the returned message.
• pathname — the original pathname, exactly as passed to the execvp(3) system call.
• argv — the original argv, exactly as passed to the execvp(3) system call.

🧚 explain_message_errno_execvp 🧚

void explain_message_errno_execvp(char *message, int message_size, int errnum, const char *pathname, char *const *argv);

the explain_message_errno_execvp function may be used to obtain an explanation of an error returned by the execvp(3) system call. the least the message will contain is the value of strerror(errnum), but usually it does so much better and reveals the underlying cause in more detail. ⭐

you're meant to use it in a fashion similar to this:

if (execvp(pathname, argv) < 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_execvp(message, sizeof(message),
        err, pathname, argv);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

the code example above is available pre‐packaged as the explain_execvp_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 global variable errno right 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. 💀
• pathname — the original pathname, exactly as passed to the execvp(3) system call.
• argv — the original argv, exactly as passed to the execvp(3) system call.

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👀 SEE ALSO 👀

• execvp(3) — execute a file
• explain_execvp_or_die(3) — execute a file and report errors

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💌 COPYRIGHT 💌

okay that's the whole page, bestie, hope you slayed 🫶 and before you go — this is libexplain version 1.4, and the copyright is held by Peter Miller, Copyright (C) 2009 Peter Miller. periodt. 💅✨