openssl: how to read a .crt file..?

I want to read the certifi.crt file using 开发者_开发技巧OpenSSL API (not in commands). I have no idea how to do that. If any one knows, please help me. Thank you.

If you give example code that will be very helpful.

If the ".crt" extension refers to a PEM text file (begins with -----BEGIN CERTIFICATE----- followed by base64), then get started in the OpenSSL docs here.

Here is some code to get you started (link with ssl, e.g. g++ a.c -lssl):

#include <stdio.h>
#include <openssl/x509.h>
#include <openssl/pem.h>

int main(int argc, char** argv)
{
    FILE* f = fopen("certifi.crt", "r");
    if (f != NULL)
    {
        X509* x509 = PEM_read_X509(f, NULL, NULL, NULL);
        if (x509 != NULL)
        {
            char* p = X509_NAME_oneline(X509_get_issuer_name(x509), 0, 0);
            if (p)
            {
                printf("NAME: %s\n", p);
                OPENSSL_free(p);
            }
            X509_free(x509);
        }
    }
    return 0;
}