DYNARR(3pub)

💖 DYNARR — the 3pub girlies' guide to simple dynamic arrays 💖

okay so bestie, welcome to DYNARR(3pub), straight out of the C Programmer's Manual. This is the page about dynarr, dynarr_init, dynarr_resize and dynarr_free — literally just simple dynamic arrays. No cap. 🌸

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✨ NAME ✨

dynarr, dynarr_init, dynarr_resize, dynarr_free — simple dynamic arrays 🦋

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🌈 SYNOPSIS 🌈

#include <publib.h>

void dynarr_init(struct dynarr *da, size_t elsize);
int dynarr_resize(struct dynarr *da, size_t newsize);
void dynarr_free(struct dynarr *da);

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💅 DESCRIPTION 💅

These functions make it easier to use dynamic arrays — and by that we mean arrays that get allocated with malloc(3) and resized with realloc(3). The way that everyone hand-rolls this is lowkey a mess, so let's look at the typical code fragment for implementing a dynamic array that gets resized as more input is read. 👑

char *p, *line;
size_t alloc, len;

len = 0;
alloc = 1024;
if ((line = malloc(alloc)) == NULL) abort();

while (fgets(line + len, alloc-len, stdin) != NULL) {
     len = strlen(line);
     alloc += 1024;
     if ((p = realloc(alloc)) == NULL) abort();
     alloc = p;
}

(The error handling is intentionally simplified.) Girl, they told us themselves. 🙈

And now the same fragment but with the dynarr(3) glow-up:

struct dynarr da;

dynarr_init(&da);
while (fgets((char *)da.data + da.used, da.alloc-da.len, stdin) != NULL) {
     da.used = strlen(da.data);
     if (dynarr_resize(&da, da.alloc + 1024) == -1) abort();
}

It's giving cleaner code, fr fr. The code is a bit simpler, and all the memory allocation details plus most of the error checking code are hidden away. Obsessed. ✨

The dynamic array is represented by a struct dynarr:

struct dynarr {
    void *data;
    size_t alloc, used;
};

The interface to the dynamic allocation has intentionally been made unopaque. Yes bestie, on purpose, not a mistake. 💅

So here's the rundown, one function at a time:

• dynarr_init — initializes a struct dynarr to be an empty array. Fresh start, main character energy. 🎀
• dynarr_resize — sets its size to be newsize. Glow-up arc. 🦋
• dynarr_free — frees the array (it will become an empty array again). Closure, we love to see it. 🌸

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🫶 RETURNS 🫶

dynarr_resize returns -1 if it failed, and 0 if it succeeded.

⚠️ And listen — it does not change the array in any way if it failed. So if it flops, your array is untouched. No damage, no drama. 💀

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👑 SEE ALSO 👑

publib(3), malloc(3), realloc(3), strdup(3) — the whole friend group, iykyk. 🧚

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💜 AUTHOR 💜

Lars Wirzenius (lars.wirzenius@helsinki.fi) — icon, legend, the moment. 👑

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okay that's the whole page bestie, go write some arrays 💖

This was Publib, from the C Programmer's Manual, section DYNARR(3pub) — mwah, slay, periodt. 💅✨🎀