From 018294242819ed59e708e23cf40b822e843ec3ac Mon Sep 17 00:00:00 2001
From: Garrett D'Amore <garrett@damore.org>
Date: Tue, 22 Oct 2024 14:10:47 -0700
Subject: docs: add memory chapter

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 docs/ref/api/memory.md | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 docs/ref/api/memory.md

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+# Memory
+
+Managing {{i:memory}} and {{i:allocations}} is something that every C program has to deal with.
+In the case of _NNG_, it can be more complicated because the underlying platform
+code can provide different allocators that might not be compatible with the use
+system allocator used by `malloc` and `free`.
+
+## Allocate Memory
+
+```c
+void *nng_alloc(size_t size);
+```
+
+The {{i:`nng_alloc`}} function allocates a contiguous memory region of
+at least _size_ bytes, and returns a pointer to it.
+The memory will be 64-bit aligned.
+Note that the memory may have random data in it, just like with `malloc`.
+
+If memory cannot be allocated for any reason, then `NULL` will be returned.
+Applications that experience this should treat this like `NNG_ENOMEM`.
+
+Memory returned by `nng_alloc` can be used to hold message buffers, in which
+case it can be directly passed to [`nng_send`][nng_send] using the flag `NNG_FLAG_ALLOC`.
+Alternatively, it can be freed when no longer needed using [`nng_free`][nng_free].
+
+> [!IMPORTANT]
+> Do not use the system `free` function (or the C++ `delete` operator) to release this memory.
+> On some configurations this may work, but on others it will lead to a crash or
+> other unpredictable behavior.
+
+## Deallocate Memory
+
+```c
+void nng_free(void *ptr, size_t size);
+```
+
+The {{i:`nng_free`}} function deallocates memory previously allocated by [`nng_alloc`][nng_alloc].
+
+The _size_ argument must exactly match the _size_ argument that was supplied to
+`nng_alloc` when the memory was allocated.
+
+## Duplicate String
+
+```c
+char *nng_strdup(const char *src);
+```
+
+The {{i:`nng_strdup`}} duplicates the string _src_ and returns it.
+
+This is logically equivalent to using [`nng_alloc`][nng_alloc]
+to allocate a region of memory of `[c] strlen(s) + 1` bytes, and then
+using `strcpy` to copy the string into the destination before
+returning it.
+
+The returned string should be deallocated with
+[`nng_strfree`][nng_strfree], or may be deallocated using the
+[`nng_free`][nng_free] using the length of the returned string plus
+one (for the `NUL` terminating byte).
+
+## Free String
+
+```c
+void nng_strfree(char *str);
+```
+
+The {{i:`nng_strfree`}} function is a convenience function that
+can be used to deallocate strings allocated with [`nng_strdup`][nng_strdup].
+
+It is effectively the same as `[c] nng_free(strlen(str) + 1)`.
+
+[nng_alloc]: #allocate-memory
+[nng_free]: #deallocate-memory
+[nng_strdup]: #duplicate-string
+[nng_strfree]: #free-string
+[nng_send]: TODO.md
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