Other example for DH and ECC from:
https://github.com/bumptech/stud/blob/master/stud.c

#ifndef OPENSSL_NO_DH
static int init_dh(SSL_CTX *ctx, const char *cert) {
    DH *dh;
    BIO *bio;

    assert(cert);

    bio = BIO_new_file(cert, "r");
    if (!bio) {
      ERR_print_errors_fp(stderr);
      return -1;
    }

    dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
    BIO_free(bio);
    if (!dh) {
        ERR("{core} Note: no DH parameters found in %s\n", cert);
        return -1;
    }

    LOG("{core} Using DH parameters from %s\n", cert);
    SSL_CTX_set_tmp_dh(ctx, dh);
    LOG("{core} DH initialized with %d bit key\n", 8*DH_size(dh));
    DH_free(dh);

#ifdef NID_X9_62_prime256v1
    EC_KEY *ecdh = NULL;
    ecdh = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
    SSL_CTX_set_tmp_ecdh(ctx,ecdh);
    EC_KEY_free(ecdh);
    LOG("{core} ECDH Initialized with NIST P-256\n");
#endif

    return 0;
}
#endif /* OPENSSL_NO_DH */