How to verify that DH private and public key have been generated ?

[ikuzar]

Hello,
I 'd like to know how to verify that DH private and public key have been
generated ?
In my DH struct, p and g had been generated with commands line ( openssl
dhparam... )

struct
        {
        BIGNUM *p;              // prime number (shared)
        BIGNUM *g;              // generator of Z_p (shared)
        BIGNUM *priv_key;       // private DH value x
        BIGNUM *pub_key;        // public DH value g^x
        // ...
        };
 DH


Priv_key and pub_key are generated later with DH_generate_key(dh).

I would like verify if DH_generate_key( ) has generated the priv_key ( an
human proof, example by using DHparams_print_fp(fp, dh ); ) I used this
function but it did not print private key into file pointed by fp.

Thanks for your help.