Visual Studio 2012 - "Error LNK2019 unresolved external symbol" when attempting to include .lib

Question

I am trying to include a .lib file in my Visual Studio 2012 C++ project. The library is the pHash project to be specific. I have added the header file for the project to Project->Properties->Configuration Properties->VC++ Directories->Includes and the .lib file's folder to Project->Properties->Configuration Properties->VC++ Directories->Library Directories. pHash.lib has been added to the list of dependencies inProject->Properties->Configuration Properties->Linker->Input->Additional Dependencies. But even though I have done all of this I still get this error when trying to use the libraries: error LNK2019: unresolved external symbol "int __cdecl ph_dct_imagehash(char const *,unsigned __int64 &)" (?ph_dct_imagehash@@YAHPBDAA_K@Z) referenced in function _main.

My code looks as follows:

#include <iostream>
#include "pHash.h"

using namespace std;

int ph_dct_imagehash(const char *file, ulong64 &hash);

int main()
{
   ulong64 tmp = 0;
   ulong64 &hash = tmp;
   const char *file = "C:\\users\\user\\desktop\\img1.jpg";

   ph_dct_imagehash(file, hash);

   return 0;
}

Try #include now you've been to the trouble of setting the include path properly. (note <> not "") — doctorlove, Sep 16 '13 at 11:27
Are you building the lib as part of the solution, or adding a pre-built lib ? — Kindread, Sep 16 '13 at 11:28
@Kindread I'm adding a pre-built lib. (Actually I built the lib myself from the pHash project files) — user1049697, Sep 16 '13 at 11:58
Possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — Ken White, Feb 07 '19 at 02:37

score 0 · Answer 1 · answered Sep 16 '13 at 11:25

0

You will not need the prototype

int ph_dct_imagehash(const char *file, ulong64 &hash);

after including pHash.h as the latter will declare the functions for you.

Remove that line and examine any compiler error (which, if any, will be something on the lines of not being able to find the function ph_dct_imagehash). Perhaps you'll need to prefix with a correct namespace:

somephashnamespace::ph_dct_imagehash(file, hash);

answered Sep 16 '13 at 11:25

Bathsheba

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I suspect this is a C library so won't have a namespace - it will be interesting to see what happens when the prototype gets removed. – doctorlove Sep 16 '13 at 11:30
Removing the prototype just makes the function call undefined. – user1049697 Sep 16 '13 at 11:57
@user1049697, I was counting on that. Read the docs to see how you should properly include ph_dct_imagehash and what namespace it's in, if any. – Bathsheba Sep 16 '13 at 11:59
@Bathsheba The documentation doesn't provide any more info than the prototype and parameters. I don't think it's in a namespace either. – user1049697 Sep 16 '13 at 12:16
@user1049697; do a global search for the ph_dct_imagehash and see what header it's in. Include that. – Bathsheba Sep 16 '13 at 12:39
@Bathsheba It is in the `pHash.h` header which is already included. – user1049697 Sep 16 '13 at 12:59
@user1049697; could you tell me the actual prototype? Either in comment or amend the question text? – Bathsheba Sep 16 '13 at 13:01
@Bathsheba The prototype from the headerfile is int ph_dct_imagehash(const char* file,ulong64 &hash); – user1049697 Sep 16 '13 at 13:15
@user1049697; now it's time to implement doctorlove's suggestion. Are you sure the function is not #ifdef'd out in the include file? – Bathsheba Sep 16 '13 at 13:19
@Bathsheba There are some #ifdefs in the include. Doing as Doctorlove suggests and including doesn't help since it doesn't exist. – user1049697 Sep 16 '13 at 13:35
@user1049697: doctorlove has a typo. He meant – Bathsheba Sep 16 '13 at 13:35
@Bathsheba Yeah, I figured as much so I tried as well. :) But it doesn't make much difference. – user1049697 Sep 16 '13 at 13:53
Does it make some difference? How is ulong64 defined? – doctorlove Sep 16 '13 at 14:24
@doctorlove It doesn't make any difference on the output. ulong64 is defined as follows: typedef unsigned long long ulong64; – user1049697 Sep 16 '13 at 14:34

Visual Studio 2012 - "Error LNK2019 unresolved external symbol" when attempting to include .lib

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