DEFINE_STACK_OF(3ossl)

📦

version 3.5.9 · 8 versions

3.5.9 · fedora 43, fedora 44 (latest)
3.5.9 · centos-stream 9
3.5.9 · centos-stream 10
3.5.9 · alpine 3.22
3.5.9 · alpine 3.23, alpine 3.24
3.5.8 · fedora 43
3.5.1 · fedora 43
3.5.5 · fedora 44

💅 DEFINE_STACK_OF 💅

okay bestie, welcome to the 3ossl manual page for DEFINE_STACK_OF, brought to you by OpenSSL, and it is long, so this is part 1 of 2 — hydrate, sit down, we're doing this 🫶

✨ NAME ✨

The whole squad of names this page covers, no cap:

the macros: DEFINE_STACK_OF, DEFINE_STACK_OF_CONST, DEFINE_SPECIAL_STACK_OF, DEFINE_SPECIAL_STACK_OF_CONST
the generated per-type crew: sk_TYPE_num, sk_TYPE_value, sk_TYPE_new, sk_TYPE_new_null, sk_TYPE_reserve, sk_TYPE_free, sk_TYPE_zero, sk_TYPE_delete, sk_TYPE_delete_ptr, sk_TYPE_push, sk_TYPE_unshift, sk_TYPE_pop, sk_TYPE_shift, sk_TYPE_pop_free, sk_TYPE_insert, sk_TYPE_set, sk_TYPE_find, sk_TYPE_find_ex, sk_TYPE_find_all, sk_TYPE_sort, sk_TYPE_is_sorted, sk_TYPE_dup, sk_TYPE_deep_copy, sk_TYPE_set_cmp_func, sk_TYPE_new_reserve
and the underlying utility fam: OPENSSL_sk_deep_copy, OPENSSL_sk_delete, OPENSSL_sk_delete_ptr, OPENSSL_sk_dup, OPENSSL_sk_find, OPENSSL_sk_find_ex, OPENSSL_sk_find_all, OPENSSL_sk_free, OPENSSL_sk_insert, OPENSSL_sk_is_sorted, OPENSSL_sk_new, OPENSSL_sk_new_null, OPENSSL_sk_new_reserve, OPENSSL_sk_num, OPENSSL_sk_pop, OPENSSL_sk_pop_free, OPENSSL_sk_push, OPENSSL_sk_reserve, OPENSSL_sk_set, OPENSSL_sk_set_cmp_func, OPENSSL_sk_shift, OPENSSL_sk_sort, OPENSSL_sk_unshift, OPENSSL_sk_value, OPENSSL_sk_zero

and what is all of this? a stack container 💖 periodt.

🌸 SYNOPSIS 🌸

        #include <openssl/safestack.h>

        STACK_OF(TYPE)
        DEFINE_STACK_OF(TYPE)
        DEFINE_STACK_OF_CONST(TYPE)
        DEFINE_SPECIAL_STACK_OF(FUNCTYPE, TYPE)
        DEFINE_SPECIAL_STACK_OF_CONST(FUNCTYPE, TYPE)

        typedef int (*sk_TYPE_compfunc)(const TYPE *const *a, const TYPE *const *b);
        typedef TYPE * (*sk_TYPE_copyfunc)(const TYPE *a);
        typedef void (*sk_TYPE_freefunc)(TYPE *a);

        int sk_TYPE_num(const STACK_OF(TYPE) *sk);
        TYPE *sk_TYPE_value(const STACK_OF(TYPE) *sk, int idx);
        STACK_OF(TYPE) *sk_TYPE_new(sk_TYPE_compfunc compare);
        STACK_OF(TYPE) *sk_TYPE_new_null(void);
        int sk_TYPE_reserve(STACK_OF(TYPE) *sk, int n);
        void sk_TYPE_free(STACK_OF(TYPE) *sk);
        void sk_TYPE_zero(STACK_OF(TYPE) *sk);
        TYPE *sk_TYPE_delete(STACK_OF(TYPE) *sk, int i);
        TYPE *sk_TYPE_delete_ptr(STACK_OF(TYPE) *sk, TYPE *ptr);
        int sk_TYPE_push(STACK_OF(TYPE) *sk, const TYPE *ptr);
        int sk_TYPE_unshift(STACK_OF(TYPE) *sk, const TYPE *ptr);
        TYPE *sk_TYPE_pop(STACK_OF(TYPE) *sk);
        TYPE *sk_TYPE_shift(STACK_OF(TYPE) *sk);
        void sk_TYPE_pop_free(STACK_OF(TYPE) *sk, sk_TYPE_freefunc freefunc);
        int sk_TYPE_insert(STACK_OF(TYPE) *sk, TYPE *ptr, int idx);
        TYPE *sk_TYPE_set(STACK_OF(TYPE) *sk, int idx, const TYPE *ptr);
        int sk_TYPE_find(STACK_OF(TYPE) *sk, TYPE *ptr);
        int sk_TYPE_find_ex(STACK_OF(TYPE) *sk, TYPE *ptr);
        int sk_TYPE_find_all(STACK_OF(TYPE) *sk, TYPE *ptr, int *pnum);
        void sk_TYPE_sort(const STACK_OF(TYPE) *sk);
        int sk_TYPE_is_sorted(const STACK_OF(TYPE) *sk);
        STACK_OF(TYPE) *sk_TYPE_dup(const STACK_OF(TYPE) *sk);
        STACK_OF(TYPE) *sk_TYPE_deep_copy(const STACK_OF(TYPE) *sk,
                                          sk_TYPE_copyfunc copyfunc,
                                          sk_TYPE_freefunc freefunc);
        sk_TYPE_compfunc (*sk_TYPE_set_cmp_func(STACK_OF(TYPE) *sk,
                                                sk_TYPE_compfunc compare));
        STACK_OF(TYPE) *sk_TYPE_new_reserve(sk_TYPE_compfunc compare, int n);

🦋 DESCRIPTION 🦋

So here's the whole vibe: apps can build and use their own stacks, and all you gotta do is drop any of the macros described below into a header file. Those macros are the ones that cook up typesafe inline functions that wrap themselves around the utility OPENSSL_sk_ API. And every single time you see TYPE on this page? That's just a placeholder, bestie — swap in literally any of the OpenSSL datatypes, like X509, and you're golden ✨

The STACK_OF() macro returns the name for a stack of the specified TYPE. It's an opaque pointer to a structure declaration, and you can use it in every header file that references the stack. Then there are several DEFINE... macros that create static inline functions for all of the functions described on this page. Normally you'd use those in one source file, and the stack manipulation gets wrapped with application-specific functions. iykyk 💅

DEFINE_STACK_OF() creates a set of functions for a stack of TYPE elements. The type is referenced by STACK_OF(TYPE) and each function name begins with sk_TYPE_. And DEFINE_STACK_OF_CONST() is identical to DEFINE_STACK_OF() except each element is constant 🎀

        /* DEFINE_STACK_OF(TYPE) */
        TYPE *sk_TYPE_value(STACK_OF(TYPE) *sk, int idx);
        /* DEFINE_STACK_OF_CONST(TYPE) */
        const TYPE *sk_TYPE_value(STACK_OF(TYPE) *sk, int idx);

DEFINE_SPECIAL_STACK_OF() and DEFINE_SPECIAL_STACK_OF_CONST() are similar, except FUNCNAME is used in the function names:

        /* DEFINE_SPECIAL_STACK_OF(TYPE, FUNCNAME) */
        TYPE *sk_FUNCNAME_value(STACK_OF(TYPE) *sk, int idx);
        /* DEFINE_SPECIAL_STACK_OF(TYPE, FUNCNAME) */
        const TYPE *sk_FUNCNAME_value(STACK_OF(TYPE) *sk, int idx);

🌈 the function rundown, one by one 🌈

sk_TYPE_num() — returns the number of elements in sk, or -1 if sk is NULL.
sk_TYPE_value() — returns element idx in sk, where idx starts at zero. If idx is out of range then NULL is returned.
sk_TYPE_new() — allocates a new empty stack using comparison function compare. If compare is NULL then no comparison function is used. This function is equivalent to sk_TYPE_new_reserve(compare, 0).
sk_TYPE_new_null() — allocates a new empty stack with no comparison function. This function is equivalent to sk_TYPE_new_reserve(NULL, 0).
sk_TYPE_reserve() — allocates additional memory in the sk structure such that the next n calls to sk_TYPE_insert(), sk_TYPE_push() or sk_TYPE_unshift() will not fail or cause memory to be allocated or reallocated. If n is zero, any excess space allocated in the sk structure is freed. On error sk is unchanged.
sk_TYPE_new_reserve() — allocates a new stack. The new stack will have additional memory allocated to hold n elements if n is positive. The next n calls to sk_TYPE_insert(), sk_TYPE_push() or sk_TYPE_unshift() will not fail or cause memory to be allocated or reallocated. If n is zero or less than zero, no memory is allocated. sk_TYPE_new_reserve() also sets the comparison function compare to the newly created stack. If compare is NULL then no comparison function is used.
sk_TYPE_set_cmp_func() — sets the comparison function of sk to compare. The previous comparison function is returned, or NULL if there was no previous comparison function.
sk_TYPE_free() — frees up the sk structure. It does not free up any elements of sk.

after this call sk is no longer valid, bestie. it's giving expired 💀 do not touch it.

sk_TYPE_zero() — sets the number of elements in sk to zero. It does not free sk, so after this call sk is still valid 🫶
sk_TYPE_pop_free() — frees up all elements of sk and sk itself. The free function freefunc() is called on each element to free it.
sk_TYPE_delete() — deletes element i from sk. It returns the deleted element, or NULL if i is out of range.
sk_TYPE_delete_ptr() — deletes element matching ptr from sk. It returns the deleted element, or NULL if no element matching ptr was found.
sk_TYPE_insert() — inserts ptr into sk at position idx. Any existing elements at or after idx are moved downwards. If idx is out of range the new element is appended to sk. sk_TYPE_insert() either returns the number of elements in sk after the new element is inserted, or zero if an error (such as memory allocation failure) occurred.
sk_TYPE_push() — appends ptr to sk; it is equivalent to:

        sk_TYPE_insert(sk, ptr, -1);

sk_TYPE_unshift() — inserts ptr at the start of sk; it is equivalent to:

        sk_TYPE_insert(sk, ptr, 0);

sk_TYPE_pop() — returns and removes the last element from sk.
sk_TYPE_shift() — returns and removes the first element from sk.
sk_TYPE_set() — sets element idx of sk to ptr, replacing the current element. The new element value is returned, or NULL if an error occurred: this will only happen if sk is NULL or idx is out of range.
sk_TYPE_find() — searches sk for the element ptr. In the case where no comparison function has been specified, the function performs a linear search for a pointer equal to ptr. In the case where a comparison function has been specified, the function performs a search for a element that the comparison function indicates is a match. If the stack is sorted, a binary search is used, otherwise, a linear search is used. sk_TYPE_find() returns the index of a matching element, or -1 if there is no match.
sk_TYPE_find_ex() — operates like sk_TYPE_find() except when a comparison function has been specified and no matching element is found. Instead of returning -1, sk_TYPE_find_ex() returns the index of the element either before or after the location where ptr would be if it were present in sk. The function also does not guarantee that the first matching element in the sorted stack is returned. (yes, it's the chaotic one, and that's the whole point 🙈)
sk_TYPE_find_all() — operates like sk_TYPE_find() but it also sets the *pnum to number of matching elements in the stack. In case no comparison function has been specified the *pnum will be always set to 1 if matching element was found, 0 otherwise.
sk_TYPE_sort() — sorts sk using the supplied comparison function.
sk_TYPE_is_sorted() — returns 1 if sk is sorted and 0 otherwise.
sk_TYPE_dup() — returns a shallow copy of sk, or an empty stack if the passed stack is NULL. Note the pointers in the copy are identical to the original. (shallow = the vibes are shared, not cloned 🦋)
sk_TYPE_deep_copy() — returns a new stack where each element has been copied, or an empty stack if the passed stack is NULL. Copying is performed by the supplied copyfunc() and freeing by freefunc().

heads up: the function freefunc() is only called if an error occurs. not on a happy path, not as cleanup — only on error. don't forget it 💖

NOTES 🧠✨

okay bestie, before you go wild with stacks, read this, because it's giving “important safety briefing” energy.

Threads? Be careful. Any operation that makes a stack bigger — like sk_TYPE_insert() or sk_TYPE_push() — can “grow” the size of an internal array, and that can cause race conditions if the same stack is accessed in a different thread. Also sk_TYPE_find() and sk_TYPE_sort() can reorder the stack, so yeah, same caution applies. multithreaded chaos is not the vibe 💀
Any comparison function you supply should use a metric suitable for a binary search operation. That means it should return zero, a positive value, or a negative value if a is equal to, greater than, or less than b, respectively. (Basically: 0 = same, + = a bigger, - = b bigger. Slay.) ✨
Watch those find return values, fr fr. sk_TYPE_find() and sk_TYPE_find_ex() return an index to the matching element. And here's the trap: 0 means a matching first element. A failed search is indicated by a -1 return value. So don't treat 0 as “nothing found” — that's not it, bestie. 🙈
STACK_OF(), DEFINE_STACK_OF(), DEFINE_STACK_OF_CONST(), and DEFINE_SPECIAL_STACK_OF() are implemented as macros. iykyk 💅
It is not an error to call sk_TYPE_num(), sk_TYPE_value(), sk_TYPE_free(), sk_TYPE_zero(), sk_TYPE_pop_free(), sk_TYPE_delete(), sk_TYPE_delete_ptr(), sk_TYPE_pop(), sk_TYPE_shift(), sk_TYPE_find(), sk_TYPE_find_ex(), and sk_TYPE_find_all() on a NULL stack, an empty stack, or with an invalid index. An error is not raised in these conditions. no drama, no error 🫶
The underlying utility OPENSSL_sk_ API should not be used directly. It defines these functions: OPENSSL_sk_deep_copy(), OPENSSL_sk_delete(), OPENSSL_sk_delete_ptr(), OPENSSL_sk_dup(), OPENSSL_sk_find(), OPENSSL_sk_find_ex(), OPENSSL_sk_find_all(), OPENSSL_sk_free(), OPENSSL_sk_insert(), OPENSSL_sk_is_sorted(), OPENSSL_sk_new(), OPENSSL_sk_new_null(), OPENSSL_sk_new_reserve(), OPENSSL_sk_num(), OPENSSL_sk_pop(), OPENSSL_sk_pop_free(), OPENSSL_sk_push(), OPENSSL_sk_reserve(), OPENSSL_sk_set(), OPENSSL_sk_set_cmp_func(), OPENSSL_sk_shift(), OPENSSL_sk_sort(), OPENSSL_sk_unshift(), OPENSSL_sk_value(), OPENSSL_sk_zero().

RETURN VALUES 💖📦

Here's what every function hands back, bestie. No guessing.

sk_TYPE_num() returns the number of elements in the stack, or -1 if the passed stack is NULL.
sk_TYPE_value() returns a pointer to a stack element, or NULL if the index is out of range.
sk_TYPE_new(), sk_TYPE_new_null(), and sk_TYPE_new_reserve() return an empty stack, or NULL if an error occurs.
sk_TYPE_reserve() returns 1 on successful allocation of the required memory, or 0 on error.
sk_TYPE_set_cmp_func() returns the old comparison function, or NULL if there was no old comparison function.
sk_TYPE_free(), sk_TYPE_zero(), sk_TYPE_pop_free(), and sk_TYPE_sort() do not return values. (Iconic no-return energy. 🎀)
sk_TYPE_pop(), sk_TYPE_shift(), sk_TYPE_delete(), and sk_TYPE_delete_ptr() return a pointer to the deleted element, or NULL on error.
sk_TYPE_insert(), sk_TYPE_push(), and sk_TYPE_unshift() return the total number of elements in the stack, and 0 if an error occurred.
sk_TYPE_set() returns a pointer to the replacement element, or NULL on error.
sk_TYPE_find() and sk_TYPE_find_ex() return an index to the found element, or -1 on error.
sk_TYPE_is_sorted() returns 1 if the stack is sorted and 0 if it is not.
sk_TYPE_dup() and sk_TYPE_deep_copy() return a pointer to the copy of the stack, or NULL on error.

HISTORY 🕰️🌈

Before OpenSSL 1.1.0, this was implemented via macros and not inline functions, and was not a public API. ancient lore ✨
sk_TYPE_reserve() and sk_TYPE_new_reserve() were added in OpenSSL 1.1.1.
From OpenSSL 3.2.0, the sk_TYPE_find(), sk_TYPE_find_ex(), and sk_TYPE_find_all() calls are read-only and do not sort the stack. To avoid any performance implications this change introduces, sk_TYPE_sort() should be called before these find operations. so sort first, bestie 🔥
Before OpenSSL 3.3.0, sk_TYPE_push() returned -1 if sk was NULL. It was changed to return 0 in this condition as for other errors. glow-up moment 💅

COPYRIGHT 📜💖

Licensed under the Apache License 2.0 (the “License”). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

And that's the whole vibe check, bestie. The footer on this one says it's version 3.5.9, dated 2026-09-29, and it's the DEFINE_STACK_OF(3ossl) page. Go forth and stack responsibly. 💖✨

📦 where this page comes from

fedora 43: openssl-devel 1:3.5.9-1.fc43 · Apache-2.0
fedora 43: openssl-devel 1:3.5.9-1.fc43 · Apache-2.0
fedora 44: openssl-devel 1:3.5.9-1.fc44 · Apache-2.0
fedora 44: openssl-devel 1:3.5.9-1.fc44 · Apache-2.0
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on 2026-10-14: a language model's rewrite of the original, under its terms