- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- HISTORY

# NAME

BN_CTX_new, BN_CTX_init, BN_CTX_free - allocate and free BN_CTX structures

# SYNOPSIS

     #include <openssl/bn.h>

     BN_CTX *BN_CTX_new(void);

     void BN_CTX_init(BN_CTX *c);

     void BN_CTX_free(BN_CTX *c);

# DESCRIPTION

A BN_CTX is a structure that holds BIGNUM temporary variables used by library functions. Since dynamic memory allocation to create BIGNUMs is rather expensive when used in conjunction with repeated subroutine calls, the BN_CTX structure is used.

`BN_CTX_new()` allocates and initializes a BN_CTX structure. `BN_CTX_init()` initializes an existing uninitialized BN_CTX.

`BN_CTX_free()` frees the components of the BN_CTX, and if it was created by `BN_CTX_new()`, also the structure itself. If BN_CTX_start has been used on the BN_CTX, BN_CTX_end must be called before the BN_CTX may be freed by `BN_CTX_free()`.

# RETURN VALUES

`BN_CTX_new()` returns a pointer to the BN_CTX. If the allocation fails, it returns NULL and sets an error code that can be obtained by ERR_get_error.

`BN_CTX_init()` and `BN_CTX_free()` have no return values.

# SEE ALSO

bn, ERR_get_error, BN_add, BN_CTX_start

# HISTORY

`BN_CTX_new()` and `BN_CTX_free()` are available in all versions on SSLeay and OpenSSL. `BN_CTX_init()` was added in SSLeay 0.9.1b.