- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- HISTORY
- COPYRIGHT

# NAME

DEFINE_STACK_OF, DEFINE_STACK_OF_CONST, DEFINE_SPECIAL_STACK_OF, DEFINE_SPECIAL_STACK_OF_CONST, 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_sort, sk_TYPE_is_sorted, sk_TYPE_dup, sk_TYPE_deep_copy, sk_TYPE_set_cmp_func, sk_TYPE_new_reserve - stack container

# 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(const STACK_OF(TYPE) *sk);
     void sk_TYPE_zero(const 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);
     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

Applications can create and use their own stacks by placing any of the macros described below in a header file. These macros define typesafe inline functions that wrap around the utility OPENSSL_sk_ API. In the description here, TYPE is used as a placeholder for any of the OpenSSL datatypes, such as X509.

`STACK_OF()` returns the name for a stack of the specified TYPE. `DEFINE_STACK_OF()` creates set of functions for a stack of TYPE. This will mean that type TYPE is stored in each stack, the type is referenced by STACK_OF(TYPE) and each function name begins with sk_TYPE_. For example:

     TYPE *sk_TYPE_value(STACK_OF(TYPE) *sk, int idx);

`DEFINE_STACK_OF_CONST()` is identical to `DEFINE_STACK_OF()` except each element is constant. For example:

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

`DEFINE_SPECIAL_STACK_OF()` defines a stack of TYPE but each function uses FUNCNAME in the function name. For example:

     TYPE *sk_FUNCNAME_value(STACK_OF(TYPE) *sk, int idx);

`DEFINE_SPECIAL_STACK_OF_CONST()` is similar except that each element is constant:

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

`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.

`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. The index of the first matching element is returned or -1 if there is no match. In the case where a comparison function has been specified, sk is sorted then `sk_TYPE_find()` returns the index of a matching element or -1 if there is no match. Note that, in this case, the matching element returned is not guaranteed to be the first; the comparison function will usually compare the values pointed to rather than the pointers themselves and the order of elements in sk could change.

`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.

`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 copy of sk. Note the pointers in the copy are identical to the original.

`sk_TYPE_deep_copy()` returns a new stack where each element has been copied. Copying is performed by the supplied `copyfunc()` and freeing by `freefunc()`. The function `freefunc()` is only called if an error occurs.

# NOTES

Care should be taken when accessing stacks in multi-threaded environments. Any operation which increases the size of a stack such as `sk_TYPE_insert()` or `sk_push()` can "grow" the size of an internal array and cause race conditions if the same stack is accessed in a different thread. Operations such as `sk_find()` and `sk_sort()` can also reorder the stack.

Any comparison function supplied should use a metric suitable for use in a binary search operation. That is it should return zero, a positive or negative value if a is equal to, greater than or less than b respectively.

Care should be taken when checking the return values of the functions `sk_TYPE_find()` and `sk_TYPE_find_ex()`. They return an index to the matching element. In particular 0 indicates a matching first element. A failed search is indicated by a -1 return value.

`STACK_OF()`, `DEFINE_STACK_OF()`, `DEFINE_STACK_OF_CONST()`, and `DEFINE_SPECIAL_STACK_OF()` are implemented as macros.

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_free()`, `OPENSSL_sk_insert()`, `OPENSSL_sk_is_sorted()`, `OPENSSL_sk_new()`, `OPENSSL_sk_new_null()`, `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

`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.

`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_push()` further returns -1 if sk is NULL.

`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.

# HISTORY

Before OpenSSL 1.1.0, this was implemented via macros and not inline functions and was not a public API.

`sk_TYPE_reserve()` and `sk_TYPE_new_reserve()` were added in OpenSSL 1.1.1.

# COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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.