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DYNARR(3pub) C Programmer's Manual DYNARR(3pub)


dynarr, dynarr_init, dynarr_resize, dynarr_free - simple dynamic arrays


#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);


These functions make it easier to use dynamic arrays, i.e., arrays that are allocated with malloc(3) and resized with realloc(3). Below is a typical code fragment for implementing a dynamic array that is 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.) Below is the above fragment with the dynarr(3).

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

The code is a bit simpler, and all the memory allocation details and most of the error checking code is hidden away.

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.

dynarr_init initializes a struct dynarr to be an empty array, dynarr_resize sets its size to be newsize, and dynarr_free frees the array (it will become an empty array again).


dynarr_resize returns -1 if it failed, 0 if it succeeded. It does not change the array in any way if it failed.


publib(3), malloc(3), realloc(3), strdup(3)


Lars Wirzenius (

C Programmer's Manual Publib