POSIX_MEMALIGN(3P)

💖 POSIX_MEMALIGN(3P) 💖

okay bestie, so this one is from the POSIX Programmer's Manual (that's the whole vibe of the 3P situation), and before we even get into it:

Heads up, queen: the Linux implementation of this interface may differ — so if you're on Linux, go read the corresponding Linux manual page for the deets on Linux behavior. Or honestly? The interface might just not be implemented on Linux at all. 💀 Not every system shows up to the party.

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✨ NAME ✨

posix_memalign — aligned memory allocation (ADVANCED REALTIME)

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🌸 SYNOPSIS 🌸

#include <stdlib.h>

int posix_memalign(void **memptr, size_t alignment, size_t size);

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🦋 DESCRIPTION 🦋

So what's the tea. The posix_memalign() function shall allocate size bytes, aligned on a boundary that you specify with alignment, and it shall hand you back a pointer to that allocated memory in memptr. 🫶

The value of alignment shall be a power of two multiple of sizeof(void *). That's the rule. No exceptions, no negotiating. 👑

Once it's done successfully, the value pointed to by memptr shall be a multiple of alignment. Slay.

Now, if the size of the space requested is 0, bestie, the behavior is implementation-defined, so it's giving "choose your own adventure": either a null pointer shall be returned in memptr, or the behavior shall be as if the size were some non-zero value — except that the behavior is undefined if the value returned in memptr is used to access an object. 🚨 So don't touch it. Seriously.

And the free() function shall deallocate memory that was previously allocated by posix_memalign(). Matching set. ✨

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💅 RETURN VALUE 💅

Upon successful completion, posix_memalign() shall return zero. Otherwise, an error number shall be returned to indicate the error, and the contents of memptr shall either be left unmodified or be set to a null pointer.

If size is 0, either:

• posix_memalign() shall not attempt to allocate any space, in which case either an implementation-defined error number shall be returned, or zero shall be returned with a null pointer returned in memptr, or
• posix_memalign() shall attempt to allocate some space and, if the allocation succeeds, zero shall be returned and a pointer to the allocated space shall be returned in memptr. And the application shall ensure that the pointer is not used to access an object. 🙈

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🔥 ERRORS 🔥

The posix_memalign() function shall fail if:

• EINVAL — The value of the alignment parameter is not a power of two multiple of sizeof(void *).
• ENOMEM — There is insufficient memory available with the requested alignment.

The following sections are informative.

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🎀 EXAMPLES 🎀

The following example shows how applications can obtain consistent behavior on error by setting *memptr to be a null pointer before calling posix_memalign().

void *ptr = NULL;
...
//do some work, which might goto error
if (posix_memalign(&ptr, align, size))
    goto error;

//do some more work, which might goto error
...
error:
    free(ptr);
    //more cleanup;

ngl, setting ptr = NULL first is the lowkey genius move here — that way your cleanup path is always safe even if things go sideways. 🧚

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🌈 APPLICATION USAGE 🌈

The posix_memalign() function is part of the Advisory Information option and need not be provided on all implementations. So like… vibe check your platform first, iykyk.

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⭐ RATIONALE ⭐

None.

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🍓 FUTURE DIRECTIONS 🍓

None.

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💜 SEE ALSO 💜

free(), malloc()

The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

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👑 COPYRIGHT 👑

Okay so this part is the boring-but-legally-required section and we do not skip it, periodt. Here's the whole thing:

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie 💖 this icon was brought to you by IEEE/The Open Group, dated 2017, filed under POSIX_MEMALIGN(3P) — go forth and align your memory, you gorgeous thing ✨🫶