openssl - How can I use openssl RSA public key to decrypt with out read the pem file

Question

I send a string of the client's public key from a pem file and want to use this string to do decryption on server without writing the string into another pem file. How can I do it?

read key code:

if ( (my_public_key = PEM_read_RSA_PUBKEY(fp, NULL, My_PWD, NULL)) == NULL) {
    ERR_print_errors_fp(stdout);
    fclose(fp);
    return;
}

do decrypt code:

rsa_len = RSA_size(target_public_key);
p_de = (unsigned char*)malloc(rsa_len+1);
memset(p_de, 0, rsa_len+1);
if (RSA_public_decrypt(rsa_len, (unsigned char*)from_hex,p_de , target_public_key, RSA_NO_PADDING) <0) {
    perror("can't decrypt data!");
    return;
}