How to compile program with OpenSSL on Windows with MinGW

Question

I tried running this sample code from fm4dd.com. But I don't know how to actually include the header files into my program. Orignally it was like:

#include <openssl/bio.h>

But i changes it to their actual path, but an error still shows up.

#include <C:\openssl\include\openssl\bio.h>
#include <C:\openssl\include\openssl\err.h>
#include <C:\openssl\include\openssl\pem.h>
#include <C:\openssl\include\openssl\x509.h>
#include <C:\openssl\include\openssl\e_os2.h>

int main() {

  const char cert_filestr[] = "./cert-file.pem";
             EVP_PKEY *pkey = NULL;
  BIO              *certbio = NULL;
  BIO               *outbio = NULL;
  X509                *cert = NULL;
  int ret;

  /* ---------------------------------------------------------- *
   * These function calls initialize openssl for correct work.  *
   * ---------------------------------------------------------- */
  OpenSSL_add_all_algorithms();
  ERR_load_BIO_strings();
  ERR_load_crypto_strings();

  /* ---------------------------------------------------------- *
   * Create the Input/Output BIO's.                             *
   * ---------------------------------------------------------- */
  certbio = BIO_new(BIO_s_file());
  outbio  = BIO_new_fp(stdout, BIO_NOCLOSE);

  /* ---------------------------------------------------------- *
   * Load the certificate from file (PEM).                      *
   * ---------------------------------------------------------- */
  ret = BIO_read_filename(certbio, cert_filestr);
  if (! (cert = PEM_read_bio_X509(certbio, NULL, 0, NULL))) {
    BIO_printf(outbio, "Error loading cert into memory\n");
    exit(-1);
  }

  /* ---------------------------------------------------------- *
   * Extract the certificate's public key data.                 *
   * ---------------------------------------------------------- */
  if ((pkey = X509_get_pubkey(cert)) == NULL)
    BIO_printf(outbio, "Error getting public key from certificate");

  /* ---------------------------------------------------------- *
   * Print the public key information and the key in PEM format *
   * ---------------------------------------------------------- */
  /* display the key type and size here */
  if (pkey) {
    switch (pkey->type) {
      case EVP_PKEY_RSA:
        BIO_printf(outbio, "%d bit RSA Key\n\n", EVP_PKEY_bits(pkey));
        break;
      case EVP_PKEY_DSA:
        BIO_printf(outbio, "%d bit DSA Key\n\n", EVP_PKEY_bits(pkey));
        break;
      default:
        BIO_printf(outbio, "%d bit non-RSA/DSA Key\n\n", EVP_PKEY_bits(pkey));
        break;
    }
  }

  if(!PEM_write_bio_PUBKEY(outbio, pkey))
    BIO_printf(outbio, "Error writing public key data in PEM format");

  EVP_PKEY_free(pkey);
  X509_free(cert);
  BIO_free_all(certbio);
  BIO_free_all(outbio);
  exit(0);
}

but the following error shows up every time I try to compile it on the command prompt. Since, I'm a noob, I have no clue how to proceed from here and what to do to fix this error.

c:\openssl>gcc -lssl -lcrypto -o test test.c 
In file included from test.c:1:0:
C:\openssl\include\openssl\bio.h:62:27: fatal error: openssl/e_os2.h: No such file or directory
#include <openssl/e_os2.h>
                       ^
compilation terminated.

Edit: I included the solution to the problem, but now a new error showed up:

c:\openssl>gcc -lssl -lcrypto -o test test.c -IC:\openssl\include\
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: cannot find -lssl
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: cannot find -lcrypto
collect2.exe: error: ld returned 1 exit status

Answer 1

Get rid of the full path names in your #include directives. That is, don't use #include <C:\openssl\include\openssl\bio.h>; rather, use:

#include <openssl\bio.h>
#include <openssl\err.h>
#include <openssl\pem.h>
#include <openssl\x509.h>
#include <openssl\e_os2.h>

And pass the include directory to gcc with -I:

gcc -I c:\openssl\include -o myfile myfile.c -lcrypto

Answer 2

In many cases, include-files in turn include other files. The paths of these files are specified relative, not absolute. So you have to tell your compiler, where to search for include files in general.

The -I-option is for this purpose and tells the compiler, which paths (additionally to some standard paths) are to be searched for specified include files, in your case you would use:

gcc -I C:\openssl\include

If you really need to specify an absolute include path you would use quotes, not <>, i.e.

#include "C:\foo\bar\baz.h"

but if this file includes other files, the compiler will not look specifically into C:\foo\bar for these.