Extract public key from EVP_PKEY keypair?

You could use following methods to separate public key and private key for future use.

int PEM_write_bio_PrivateKey(BIO *bp, EVP_PKEY *x, const EVP_CIPHER *enc,
                    unsigned char *kstr, int klen,
                    pem_password_cb *cb, void *u);

 int PEM_write_PrivateKey(FILE *fp, EVP_PKEY *x, const EVP_CIPHER *enc,
                    unsigned char *kstr, int klen,
                    pem_password_cb *cb, void *u);
EVP_PKEY *PEM_read_bio_PUBKEY(BIO *bp, EVP_PKEY **x,
                    pem_password_cb *cb, void *u);

 EVP_PKEY *PEM_read_PUBKEY(FILE *fp, EVP_PKEY **x,
                    pem_password_cb *cb, void *u);

 int PEM_write_bio_PUBKEY(BIO *bp, EVP_PKEY *x);
 int PEM_write_PUBKEY(FILE *fp, EVP_PKEY *x);

For detailed information, please refer to <openssl/pem.h>.

It's may be, you should use i2d_PUBKEY_bio() or similar function.