bignum.hpp:63:24: error: invalid use of incomplete type ‘BIGNUM {aka struct bignum_st}’
 class CBigNum : public BIGNUM
                        ^
In file included fromusr/local/include/openssl/bn.h:32:0,
                 from bignum.hpp:20,
                 from bignum.cpp:8:
/usr/local/include/openssl/ossl_typ.h:80:16: note: forward declaration of ‘BIGNUM {aka struct bignum_st}’
 typedef struct bignum_st BIGNUM;
                ^
In file included from bignum.cpp:8:0:
bignum.hpp: In constructor ‘CBigNum::CBigNum()’:
bignum.hpp:68:21: error: ‘BN_init’ was not declared in this scope
         BN_init(this);
                     ^
bignum.hpp: In copy constructor ‘CBigNum::CBigNum(const CBigNum&)’:
bignum.hpp:73:21: error: ‘BN_init’ was not declared in this scope
         BN_init(this);
                     ^
bignum.hpp:74:30: error: cannot convert ‘CBigNum*’ to ‘BIGNUM* {aka bignum_st*}’ for argument ‘1’ to ‘BIGNUM* BN_copy(BIGNUM*, const BIGNUM*)’