• C

How to resolve LNK2019 unresolved external symbol errors

I am using OpenSSL libraries in my C program, the IDE environment is Visual Studio .NET

The following is my sample codes:
#include <openssl/x509.h>
#include <openssl/ssl.h>
unsigned char      *p= (unsigned char *)myattr;
FILE *crtfile;
int i;
X509 *x;

crtfile = fopen("crtfile.txt", "w");
i = fwrite(p, 1, sizeof(p),crtfile);
x = d2i_X509_fp(crtfile, NULL);

This on compilation generates the following error:
error LNK2019: unresolved external symbol _d2i_X509_fp referenced in function _DisplayObjectInfo

d2i_x509_fp is a third party library function which is declared as follows:
X509 *d2i_X509_fp(FILE *fp, X509 **x509);

typedef x509_st X509;
struct x509_st
      X509_CINF *cert_info;
      X509_ALGOR *sig_alg;
      ASN1_BIT_STRING *signature;
      int valid;
      int references;
      char *name;
      CRYPTO_EX_DATA ex_data;
      /* These contain copies of various extension values */
      long ex_pathlen;
      unsigned long ex_flags;
      unsigned long ex_kusage;
      unsigned long ex_xkusage;
      unsigned long ex_nscert;
      ASN1_OCTET_STRING *skid;
      struct AUTHORITY_KEYID_st *akid;
      unsigned char sha1_hash[SHA_DIGEST_LENGTH];
      X509_CERT_AUX *aux;
      } /* X509 */;
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So, I assume the .lib format is not compatible (no standards here, *sigh*) - but, you could try to compile this one on your own, since I suppose the source code is available.
you have to link against the proper libraries. That is here the library which contains d2i_x509_fp, you should ask the developer of it.

tools->options->directories tab

select library files from the drop down box

click add (the broken lines rectangle icon)
add path to SSL library and recompile your program
Managing Security Policy in a Changing Environment

The enterprise network environment is evolving rapidly as companies extend their physical data centers to embrace cloud computing and software-defined networking. This new reality means that the challenge of managing the security policy is much more dynamic and complex.

Alternatively, add

#pragma comment ( lib, "openssl.lib")

to your code.
oohchildAuthor Commented:
I tried explicitly linking to the libraries, this time round it complains

fatal error LNK1136: invalid or corrupt file

Does it mean the libraries is corrupted?
Where did you get the libs from?
oohchildAuthor Commented:
I forgot which site I download it - it is openssl v0.9.7c GNUWin32, maybe i will link with an earlier version (0.9.6) and check if the same problem exists.
I agree with jkr ... Try recompiling the library from sources and then link to it
oohchildAuthor Commented:
I found the source of the error, the openssl library is compiled using the GnuWin32 compiler and for some reason is not compatible. After recompiling the source with nmake, it works okay. Thanks for the help. :-)
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