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Man Pages

Manual Reference Pages  -  SK_X509_NEW (3)

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sk_X509_num, sk_X509_value, sk_X509_new, sk_X509_new_null, sk_X509_free, sk_X509_zero, sk_X509_delete, sk_X509_delete_ptr, sk_X509_push, sk_X509_unshift, sk_X509_pop, sk_X509_shift, sk_X509_pop_free, sk_X509_insert, sk_X509_set, sk_X509_find, sk_X509_find_ex, sk_X509_sort, sk_X509_is_sorted, sk_X509_dup, sk_X509_deep_copy, sk_X509_set_cmp_func - X509 stack



 #include <openssl/x509.h>

 int sk_X509_num(const STACK_OF(X509) *sk);
 X509 *sk_X509_value(const STACK_OF(X509) *sk, int idx);
 STACK_OF(X509) *sk_X509_new(int (*cmpf)(const X509 * const *a,
                                         const X509 * const *b));
 STACK_OF(X509) *sk_X509_new_null(void);
 int (*sk_X509_set_cmp_func (STACK_OF(X509) *sk,
                             int (*cmpf) (const X509 * const *a,
                                          const X509 * const *b)))
                             (const X509 * const *, const X509 * const *);
 void sk_X509_free(const STACK_OF(X509) *sk);
 void sk_X509_zero(const STACK_OF(X509) *sk);
 void sk_X509_pop_free(STACK_OF(X509) *sk, void (*func) (X509 *a));
 X509 *sk_X509_delete(STACK_OF(X509) *sk, int i);
 X509 *sk_X509_delete_ptr(STACK_OF(X509) *sk, X509 *ptr);
 int sk_X509_insert(STACK_OF(X509) *sk, X509 *ptr, int idx);
 int sk_X509_push(STACK_OF(X509) *sk, X509 *ptr);
 int sk_X509_unshift(STACK_OF(X509) *sk, X509 *ptr);
 X509 *sk_X509_pop(STACK_OF(X509) *sk);
 X509 *sk_X509_shift(STACK_OF(X509) *sk);
 X509 *sk_X509_set(STACK_OF(X509) *sk, int idx, X509 *ptr);
 int sk_X509_find(STACK_OF(X509) *sk, X509 *ptr);
 int sk_X509_find_ex(STACK_OF(X509) *sk, X509 *ptr);
 void sk_X509_sort(const STACK_OF(X509) *sk);
 int sk_X509_is_sorted(const STACK_OF(X509) *sk);
 STACK_OF(X509) *sk_X509_dup(STACK_OF(X509) *sk);
 STACK_OF(X509) *sk_X509_deep_copy(STACK_OF(X509) *sk,
                                   X509 * (*copyfn) (const X509 *),
                                   void (*freefn) (X509 *));


sk_X509_num() returns the number of elements in sk or -1 if sk is NULL.

sk_X509_value() returns element idx in sk. Where idx runs from 0 to sk_X509_num(sk) - 1 inclusive. If idx is out of range then NULL is returned.

sk_X509_new() allocates a new empty stack using comparison function cmpf. If cmpf is 0 then no comparison function is used.

sk_X509_new_null() allocates a new empty stack with no comparison function.

sk_X509_set_cmp_func() sets the comparison function of sk to cmpf. The previous comparison function is returned or 0 if there was no previous comparison function.

sk_X509_free() frees up the sk structure. It does not free up any elements of sk. After this call sk is no longer valid.

sk_X509_zero() sets the number of elements in sk to zero. It does not free sk so after this call sk is still valid.

sk_X509_pop_free() frees up all elements of sk and sk itself. The free function func() is called on each element to free it.

sk_X509_delete() deletes element i from sk. It returns the deleted element or NULL if i is out of range.

sk_X509_delete_ptr() deletes element matching ptr from sk. It returns the deleted element or NULL if no element matching ptr was found.

sk_X509_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_X509_insert() either returns the number of elements in sk after the new element is inserted or zero if an error occured: which will happen if there is a memory allocation failure.

sk_X509_push() appends ptr to sk it is equivalent to:

 sk_X509_insert(sk, ptr, -1);

sk_X509_unshift() inserts ptr at the start of sk it is equivalent to:

 sk_X509_insert(sk, ptr, 0);

sk_X509_pop() returns and removes the last element from sk.

sk_X509_shift() returns and removes the first element from sk.

sk_X509_set() sets element idx of sk to ptr replacing the current element. The new element value is returned or NULL if an error occured: this will only happen if sk is NULL or idx is out of range.

sk_X509_find() and int sk_X509_find_ex() search sk using the supplied comparison function for an element matching ptr. sk_X509_find() returns the index of the first matching element or -1 if there is no match. sk_X509_find_ex() returns a matching element or the nearest element that does not match ptr. Note: if a comparison function is set then 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 ptr and the stack is not reordered.

sk_X509_sort() sorts sk using the supplied comparison function.

sk_X509_is_sorted() returns 1 if sk is sorted and 0 otherwise.

sk_X509_dup() returns a copy of sk. Note the pointers in the copy are identical to the original.

sk_X509_deep_copy() returns a new stack where each element has been copied. Copying is performed by the supplied copyfn() and freeing by freefn(). The function freefn() is only called if an error occurs.


This manual page documents the functions which operate on a stack of X509 pointers. A stack can contain pointers to any structure with X509 replaced by the appropriate structure name.

Care should be taken when accessing stacks in multi-threaded environments. Any operation which increases the size of a stack such as sk_X509_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_X509_find() and sk_X509_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.


Applications can create and use their own stacks by placing any of the macros described below in a header file.

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

 NAME *sk_NAME_value(STACK_OF(NAME) *sk, int idx);

DEFINE_STACK_OF_CONST(NAME) is identical to DEFINE_STACK_OF(NAME) except each element is constant for example:

 const NAME *sk_name_value(STACK_OF(NAME) *sk, int idx);

DEFINE_SPECIAL_STACK_OF(FNAME, STNAME) defines a stack of STNAME but each function uses FNAME. For example:

 STNAME *sk_FNAME_value(STACK_OF(STNAME) *sk, int idx);


sk_X509_num() returns the number of elements in the stack or -1 if the passed stack is NULL.

sk_X509_value() returns a pointer to a stack element or NULL if the index is out of range.

sk_X509_new() and sk_X509_new_null() return an empty stack or NULL if an error occurs.

sk_X509_set_cmp_func() returns the old comparison function or NULL if there was no old comparison function.

sk_X509_free(), sk_X509_zero(), sk_X509_pop_free() and sk_X509_sort() do not return values.

sk_X509_pop(), sk_X509_shift(), sk_X509_delete() and sk_X509_delete_ptr() return a pointer to the deleted element or NULL on error.

sk_X509_insert(), sk_X509_push() and sk_X509_unshift() return the total number of elements in the stack and 0 if an error occurred.

sk_X509_set() returns a pointer to the replacement element or NULL on error.

sk_X509_find() and sk_X509_find_ex() return an index to the found element or -1 on error.

sk_X509_is_sorted() returns 1 if the stack is sorted and 0 if it is not.

sk_X509_dup() and sk_X509_deep_copy() return a pointer to the copy of the stack.


Use of inline functions and application defined stacks first appeared in OpenSSL 1.1.0. Previous versions of OpenSSL implemented stacks as macros.
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1.1.0-pre3 SK_X509_NUM (3) 2016-02-15

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