VC++2008 error LNK2019: unresolved external symbol _MD5@12 referenced

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Hi,

I am using vc++2008 to build a C project.
In this project, I use MD5 function of openssl library.
But I have an error LNK2019 _MD5@12 reference.
I already check and sure that the "MD5" function is include in the library
"libeay32.lib".
(I already configure the "Additional Library Directory" to path to the "libeay32.lib".
But I don't understand why I could not use the function MD5 in my code.
Could any body help me to find out the cause.

Thank you very much!

P/s:
Here is my C Code:

C++

#include <stdio.h>
#include <stdlib.h>
#include <openssl\md5.h>

int __cdecl main(int argc, char *argv[])
{
    HINSTANCE hinstLib = LoadLibrary(TEXT("libssl32.dll"));
    unsigned char *input = "abc";
    unsigned char *md5;
    size_t n = 3;

    MD5(input, n, md5);


}</stdlib.h></stdio.h>

Posted 11-Oct-11 20:57pm

candd

Updated 11-Oct-11 21:00pm

Mehdi Gholam

v2

Add a Solution

3 solutions

Solution 1

You have to get the address of the function with GetProcAddress for your code to work, see below (assuming MD5 is a function in the library loaded) :

C++

int __cdecl main(int argc, char *argv[])
{
    HINSTANCE hinstLib = LoadLibrary(TEXT("libssl32.dll"));
    if(hinstLib != NULL)
    {
       FARPROC MD5;
       unsigned char *input = "abc";
       unsigned char *md5;
       size_t n = 3;
       MD5 = GetProcAddress ( hinstLib , "MD5" ) ;
       MD5(input, n, md5);
    }

}

Check the following links :

http://en.wikipedia.org/wiki/Dynamic-link_library[^]

http://forum.pellesc.de/index.php?topic=3257.0[^]

Posted 11-Oct-11 21:08pm

Mehdi Gholam

Comments

candd 12-Oct-11 5:08am

Thank yous very much for answering on my question.
> You should not be using the LoadLibrary() function in this way
Sorry because I uploaded the wrong source code.
actually my source code as bellows:

#include <stdio.h>
#include <stdlib.h>

#include <openssl\md5.h>

int __cdecl main(int argc, char *argv[])
{
unsigned char *input = "abc";
unsigned char *md5;
size_t n = 3;
MD5(input, n, md5);

}

The function "MD5" already was defined in the library "libeay32.lib".
But when I linked it in to a Win32 project ( __stdcall (/Gz) calling convention).
The bellow linker error happened .

1>Linking...
1>LINK : .\Debug\trfs.exe not found or not built by the last incremental link; performing full link
1>trfs_main.obj : error LNK2019: unresolved external symbol _MD5@12 referenced in function _main
1>.\Debug\trfs.exe : fatal error LNK1120: 1 unresolved externals

I could not understand why this linker error happened.
Could you please re-check the problem and find the solution for me!

Thank you!

Solution 2

You should not be using the LoadLibrary() function in this way, but including the library in your project. Just add the library name (libeay32.lib) to the correct entry in your project's Linker properties. Also make sure the associated DLL is either in the same directory as your EXE file or in one of the directories in your system's PATH variable.

Posted 11-Oct-11 22:36pm

Richard MacCutchan

Comments

candd 12-Oct-11 5:06am

Thank yous very much for answering on my question.
> You should not be using the LoadLibrary() function in this way
Sorry because I uploaded the wrong source code.
actually my source code as bellows:

#include <stdio.h>
#include <stdlib.h>

#include <openssl\md5.h>

int __cdecl main(int argc, char *argv[])
{
unsigned char *input = "abc";
unsigned char *md5;
size_t n = 3;
MD5(input, n, md5);

}

The function "MD5" already was defined in the library "libeay32.lib".
But when I linked it in to a Win32 project ( __stdcall (/Gz) calling convention).
The bellow linker error happened .

1>Linking...
1>LINK : .\Debug\trfs.exe not found or not built by the last incremental link; performing full link
1>trfs_main.obj : error LNK2019: unresolved external symbol _MD5@12 referenced in function _main
1>.\Debug\trfs.exe : fatal error LNK1120: 1 unresolved externals

I could not understand why this linker error happened.
Could you please re-check the problem and find the solution for me!

Thank you!

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candd · Accepted Answer · 2011-10-11T23:03:00

Thank yous very much for answering on my question.
> You should not be using the LoadLibrary() function in this way
Sorry because I uploaded the wrong source code.
actually my source code as bellows:

#include <stdio.h>
#include <stdlib.h>

#include <openssl\md5.h>

int __cdecl main(int argc, char *argv[])
{
unsigned char *input = "abc";
unsigned char *md5;
size_t n = 3;
MD5(input, n, md5);

}

The function "MD5" already was defined in the library "libeay32.lib".
But when I linked it in to a Win32 project ( __stdcall (/Gz) calling convention).
The bellow linker error happened .

1>Linking...
1>LINK : .\Debug\trfs.exe not found or not built by the last incremental link; performing full link
1>trfs_main.obj : error LNK2019: unresolved external symbol _MD5@12 referenced in function _main
1>.\Debug\trfs.exe : fatal error LNK1120: 1 unresolved externals

I could not understand why this linker error happened.
Could you please re-check the problem and find the solution for me!

Thank you!