explain_calloc(3)

✨ explain_calloc — the manual page, but make it make sense 💖

okay bestie, so this is explain_calloc from the Library Functions Manual, and it's genuinely one of those pages that's like… dry on the outside, absolute lifesaver on the inside. no cap. let's get into it 🫶

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💫 NAME

explain_calloc — it explains the errors that calloc(3) throws at you, in human words. that's the whole job. it's giving "translator for your errno" energy.

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🌸 SYNOPSIS

#include <libexplain/calloc.h>

const char *explain_calloc(size_t nmemb, size_t size);
const char *explain_errno_calloc(int errnum, size_t nmemb, size_t size);
void explain_message_calloc(char *message, int message_size, size_t nmemb, size_t size);
void explain_message_errno_calloc(char *message, int message_size, int errnum, size_t nmemb, size_t size);

like, four little functions. four little besties. each one does the same thing but with a different amount of "here, let me hold the buffer for you" energy 💅

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👑 DESCRIPTION

so basically: these functions are how you get explanations for errors returned by the calloc(3) system call. instead of just going "it broke lol" you get actual ✨insight✨.

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🎀 explain_calloc

const char *explain_calloc(size_t nmemb, size_t size);

the explain_calloc function is what you call to obtain an explanation of an error returned by the calloc(3) system call. and the least the message will contain is the value of strerror(errno) — but fr fr, usually it does way better than that and points at the actual underlying cause in more detail. slay.

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

• nmemb — the original nmemb, exactly as passed to the calloc(3) system call. don't get cute, pass it through as-is.
• size — the original size, exactly as passed to the calloc(3) system call. same deal.

Returns: the message explaining the error. and here's the tea ☕ — this message buffer is shared by all libexplain functions that don't supply a buffer in their own argument list. so it will be 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 honestly so do many other functions in this library. iykyk.

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

errno = 0;
void *result = calloc(nmemb, size);
if (!result && errno != 0)
{
    fprintf(stderr, "%s\n", explain_calloc(nmemb, size));
    exit(EXIT_FAILURE);
}

and the above code example is available pre-packaged as the explain_calloc_or_die(3) function. so if you're feeling lazy (valid), go grab that one instead 😌

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🦋 explain_errno_calloc

const char *explain_errno_calloc(int errnum, size_t nmemb, size_t size);

explain_errno_calloc is the version you reach for when you need to obtain an explanation of an error returned by the calloc(3) system call, but you've got extra steps in between. least it'll contain is the value of strerror(errno), but usually it does much better and indicates the underlying cause in more detail. iconic behaviour.

• errnum — the error value to be decoded, usually grabbed from the errno global variable right before this function is called. and this part is necessary if you need to call any code between the system call you're explaining and this function, because so many libc functions will alter the value of errno. it's giving "errno is not loyal, capture it early" 💀
• nmemb — the original nmemb, exactly as passed to the calloc(3) system call.
• size — the original size, exactly as passed to the calloc(3) system call.

Returns: the message explaining the error. and again — this message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. it will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. 😭

Note: not thread safe. shares a return buffer across all threads, plus many other functions in this library do too.

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

errno = 0;
void *result = calloc(nmemb, size);
if (!result && errno != 0)
{
    int err = errno;
    fprintf(stderr, "%s\n", explain_errno_calloc(err, nmemb, size));
    exit(EXIT_FAILURE);
}

pre-packaged as explain_calloc_or_die(3). ✨

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🌈 explain_message_calloc

void explain_message_calloc(char *message, int message_size, size_t nmemb, size_t size);

explain_message_calloc — same goal (obtain an explanation of an error returned by the calloc(3) system call), but this time you bring the buffer. 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.

the errno global variable is used to obtain 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. 👑 periodt.
• message_size — the size in bytes of the location in which to store the returned message.
• nmemb — the original nmemb, exactly as passed to the calloc(3) system call.
• size — the original size, exactly as passed to the calloc(3) system call.

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

errno = 0;
void *result = calloc(nmemb, size);
if (!result && errno != 0)
{
    char message[3000];
    explain_message_calloc(message, sizeof(message), nmemb, size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

pre-packaged as explain_calloc_or_die(3), as always 💖

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🧚 explain_message_errno_calloc

void explain_message_errno_calloc(char *message, int message_size, int errnum, size_t nmemb, size_t size);

the final boss 🐉 — explain_message_errno_calloc obtains an explanation of an error returned by the calloc(3) system call, with your own buffer and your own captured errno value. 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.

• message — the location in which to store the returned message. supply a suitable message return buffer and congrats, 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. 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. (yes, we said this before, and yes, it still matters, bestie 🫶)
• nmemb — the original nmemb, exactly as passed to the calloc(3) system call.
• size — the original size, exactly as passed to the calloc(3) system call.

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

errno = 0;
void *result = calloc(nmemb, size);
if (!result && errno != 0)
{
    int err = errno;
    char message[3000];
    explain_message_errno_calloc(message, sizeof(message), err, nmemb, size);
    fprintf(stderr, "%s\n", message);
    exit(EXIT_FAILURE);
}

pre-packaged as explain_calloc_or_die(3). every single time. 💅

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⭐ SEE ALSO

• calloc(3) — Allocate and clear memory
• explain_calloc_or_die(3) — Allocate and clear memory and report errors

like, go read those too. the vibes are immaculate and they're literally the functions this whole page keeps shouting out. 🦋

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💜 COPYRIGHT

libexplain version 1.4 Copyright (C) 2010 Peter Miller

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and that's the page!! 🌸 this was explain_calloc from the Library Functions Manual, libexplain version 1.4, copyright (C) 2010 Peter Miller — ty for coming to my ted talk, go forth and explain your calloc(3) errors with main character energy 👑💖