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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;
#ifndef OPENSSL_NO_SHA
      unsigned char sha1_hash[SHA_DIGEST_LENGTH];
#endif
      X509_CERT_AUX *aux;
      } /* X509 */;
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oohchild
Asked:
oohchild
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2 Solutions
 
fridomCommented:
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.

Regards
Friedrich
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sunnycoderCommented:
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
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jkrCommented:
Alternatively, add

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

to your code.
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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?
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jkrCommented:
Where did you get the libs from?
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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.
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jkrCommented:
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.
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sunnycoderCommented:
I agree with jkr ... Try recompiling the library from sources and then link to it
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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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