read private key out

[Wu Junwei]

Hi,all   I have a question on reading the private key out from a certificate file.   I 'd like to read a private key in a certificate file and returns the private key data and length in memroy, which functions in OpenSSL should I choose to use?   d2i/i2d_PKCS8PrivateKey_xx or PEM_read_bio_PrivateKey ?   Can some one kindly tell me the difference among them?   Thanks. wjw