From 09821002b314b7c8517f16d351b1c6b1088a47dc Mon Sep 17 00:00:00 2001
From: pommicket <pommicket@gmail.com>
Date: Mon, 15 Sep 2025 20:59:38 -0400
Subject: Better examples

---
 examples/custom_alloc.c | 93 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 examples/custom_alloc.c

(limited to 'examples/custom_alloc.c')

diff --git a/examples/custom_alloc.c b/examples/custom_alloc.c
new file mode 100644
index 0000000..42843ce
--- /dev/null
+++ b/examples/custom_alloc.c
@@ -0,0 +1,93 @@
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdalign.h>
+#include <stddef.h>
+#include <string.h>
+
+#include <pom.h>
+
+// Custom memory allocation functions
+typedef struct {
+	uint64_t allocations, frees;
+	size_t memory_used;
+	alignas(max_align_t) char memory[100000];
+} Memory;
+static void *my_calloc(void *udata, size_t nmemb, size_t sz) {
+	Memory *my_memory = udata;
+	char *mem = (char *)my_memory->memory + my_memory->memory_used;
+	size_t new_memory_used = my_memory->memory_used;
+	while ((uintptr_t)mem & 7)
+		mem++, new_memory_used++;
+	new_memory_used += 8 + nmemb * sz;
+	if (new_memory_used > sizeof my_memory->memory) {
+		// out of memory: return NULL
+		return NULL;
+	}
+	my_memory->allocations++;
+	my_memory->memory_used = new_memory_used;
+	// store size of allocation
+	*(uint64_t *)mem = nmemb * sz;
+	return mem + sizeof (uint64_t);
+}
+static void my_free(void *udata, void *ptr) {
+	if (!ptr) {
+		// free must do nothing when null pointer is passed
+		return;
+	}
+	Memory *my_memory = udata;
+	my_memory->frees++;
+}
+
+static void *my_realloc(void *udata, void *ptr, size_t new_size) {
+	if (!ptr) {
+		// realloc(ptr = NULL) is equivalent to malloc
+		return my_calloc(udata, new_size, 1);
+	}
+	// inefficient but correct realloc implementation:
+	//  just free the old memory and allocate brand new memory
+	size_t old_size = ((uint64_t *)ptr)[-1];
+	void *new_ptr = my_calloc(udata, new_size, 1);
+	if (!new_ptr) {
+		// out-of-memory: return NULL
+		return NULL;
+	}
+	memcpy(new_ptr, ptr, old_size);
+	my_free(udata, ptr);
+	return new_ptr;
+}
+
+int main(void) {
+	pom_error *error;
+	pom_settings settings = {0};
+	// set allocation functions
+	settings.calloc = my_calloc;
+	settings.realloc = my_realloc;
+	settings.free = my_free;
+	static Memory my_memory;
+	// set udata pointer which is passed to the functions
+	settings.allocator_udata = &my_memory;
+
+	pom_conf *conf = pom_load_string(&settings, "conf.pom",
+		"foo = bar\n"
+		"[core]\n"
+		"list = 1,6,78,9\n",
+		 &error);
+	if (!conf) {
+		pom_error_print(error);
+		// error must be freed with custom allocation function
+		my_free(&my_memory, error);
+		return EXIT_FAILURE;
+	}
+	char **list = pom_conf_get_list(conf, "core.list");
+	for (size_t i = 0; list[i]; i++)
+		printf("- %s\n",list[i]);
+	// lists must be freed with custom allocation function
+	my_free(&my_memory, list);
+	pom_conf_free(conf);
+	if (my_memory.allocations != my_memory.frees) {
+		// if this ever happens, it's a bug in libpom
+		fprintf(stderr, "libpom is leaking memory!!!\n");
+		return EXIT_FAILURE;
+	}
+	return 0;
+}
-- 
cgit v1.2.3