=pod

=head1 NAME

DEFINE_STACK_OF, DEFINE_STACK_OF_CONST, DEFINE_SPECIAL_STACK_OF,
sk_TYPE_num, sk_TYPE_value, sk_TYPE_new, sk_TYPE_new_null, 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 -
stack container

=head1 SYNOPSIS

 #include <openssl/safestack.h>

 #define STACK_OF(TYPE)
 #define DEFINE_STACK_OF
 #define DEFINE_STACK_OF_CONST
 #define DEFINE_SPECIAL_STACK_OF

 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);
 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, TYPE *ptr);
 int sk_TYPE_unshift(STACK_OF(TYPE) *sk, 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, 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(STACK_OF(TYPE) *sk);
 STACK_OF(TYPE) *sk_TYPE_deep_copy(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);

=head1 DESCRIPTION

Applications can create and use their own stacks by placing any of the macros
described below in a header file.  In the description below, I<TYPE> is used
as a placeholder for any of the OpenSSL datatypes, such as I<X509>.

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

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

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

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

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

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

sk_TYPE_num() returns the number of elements in B<sk> or -1 if B<sk> is
B<NULL>.

sk_TYPE_value() returns element B<idx> in B<sk>, where B<idx> starts at
zero. If B<idx> is out of range then B<NULL> is returned.

sk_TYPE_new() allocates a new empty stack using comparison function B<compar>.
If B<compar> is B<NULL> then no comparison function is used.

sk_TYPE_new_null() allocates a new empty stack with no comparison function.

sk_TYPE_set_cmp_func() sets the comparison function of B<sk> to B<compar>.
The previous comparison function is returned or B<NULL> if there was
no previous comparison function.

sk_TYPE_free() frees up the B<sk> structure. It does B<not> free up any
elements of B<sk>. After this call B<sk> is no longer valid.

sk_TYPE_zero() sets the number of elements in B<sk> to zero. It does not free
B<sk> so after this call B<sk> is still valid.

sk_TYPE_pop_free() frees up all elements of B<sk> and B<sk> itself. The
free function freefunc() is called on each element to free it.

sk_TYPE_delete() deletes element B<i> from B<sk>. It returns the deleted
element or B<NULL> if B<i> is out of range.

sk_TYPE_delete_ptr() deletes element matching B<ptr> from B<sk>. It returns
the deleted element or B<NULL> if no element matching B<ptr> was found.

sk_TYPE_insert() inserts B<ptr> into B<sk> at position B<idx>. Any existing
elements at or after B<idx> are moved downwards. If B<idx> is out of range
the new element is appended to B<sk>. sk_TYPE_insert() either returns the
number of elements in B<sk> after the new element is inserted or zero if
an error (such as memory allocation failure) occurred.

sk_TYPE_push() appends B<ptr> to B<sk> it is equivalent to:

 sk_TYPE_insert(sk, ptr, -1);

sk_TYPE_unshift() inserts B<ptr> at the start of B<sk> it is equivalent to:

 sk_TYPE_insert(sk, ptr, 0);

sk_TYPE_pop() returns and removes the last element from B<sk>.

sk_TYPE_shift() returns and removes the first element from B<sk>.

sk_TYPE_set() sets element B<idx> of B<sk> to B<ptr> replacing the current
element. The new element value is returned or B<NULL> if an error occurred:
this will only happen if B<sk> is B<NULL> or B<idx> is out of range.

sk_TYPE_find() and sk_TYPE_find_ex() search B<sk> using the supplied
comparison function for an element matching B<ptr>. sk_TYPE_find() returns
the index of the first matching element or B<-1> if there is no match.
sk_TYPE_find_ex() returns a matching element or the nearest element that
does not match B<ptr>. Note: if a comparison function is set then  B<sk> is
sorted before the search which may change its order. If no comparison
function is set then a linear search is made for a pointer matching B<ptr>
and the stack is not reordered.

sk_TYPE_sort() sorts B<sk> using the supplied comparison function.

sk_TYPE_is_sorted() returns B<1> if B<sk> is sorted and B<0> otherwise.

sk_TYPE_dup() returns a copy of B<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.

=head1 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 B<a> is equal to, greater than
or less than B<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 B<0> indicates a matching first element.
A failed search is indicated by a B<-1> return value.

=head1 RETURN VALUES

sk_TYPE_num() returns the number of elements in the stack or B<-1> if the
passed stack is B<NULL>.

sk_TYPE_value() returns a pointer to a stack element or B<NULL> if the
index is out of range.

sk_TYPE_new() and sk_TYPE_new_null() return an empty stack or B<NULL> if
an error occurs.

sk_TYPE_set_cmp_func() returns the old comparison function or B<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 B<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 B<NULL> on
error.

sk_TYPE_find() and sk_TYPE_find_ex() return an index to the found element
or B<-1> on error.

sk_TYPE_is_sorted() returns B<1> if the stack is sorted and B<0> if it is
not.

sk_TYPE_dup() and sk_TYPE_deep_copy() return a pointer to the copy of the
stack.

=head1 HISTORY

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

=head1 COPYRIGHT

Copyright 2000-2016 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
L<https://www.openssl.org/source/license.html>.

=cut