Re: Why is reference from unused function required?

David Wilkinson <>
Wed, 03 Feb 2010 10:54:15 -0500
John N. wrote:

I have stumbled across a problem involving linking to a static library
that I was hoping someone could help me with.

I want to create a static library which contains various methods that
I will use from other code. In my simple example case, I try to call
one of the two library methods from main(). Everything compiles
correctly. However, when linking, I get the link error shown below.

The source files (Methods.h, Methods.cpp, Tester.cpp) for my simple
example are typed out at the end of this post.

?Methods.h? and ?Methods.cpp? are used to build a static library named
?support library.lib?, while ?Tester.cpp? is the main() which uses one
of the two methods (method1) defined in ?Methods.cpp?.

The other method in the static library (method2) in ?Methods.cpp? is
not referenced by main(). It in turn references a method
(methodDoesNotExist) that is declared in ?Methods.h?, but is not
defined in ?Methods.cpp?. Thus, the static library compiles and is
built with no errors, yet when I go to link it with the main() I get
the link error shown below.

Why does the linker give me this link error since I am not trying to
use method2?

One way to ?fix? the problem would be to create separate .cpp/h files
for each of the methods and then use all those files to create the
static library.

Is there any way to keep all the methods in the same file (for ease of
maintenance), yet have the linker only resolve references that are

Thank you.
John N.

Small example source files begin here:

// Methods.h
#include <string>
#include <istream>

const std::string method1( std::istream& stream_ );
const std::string method2( std::istream& stream_ );
const std::string methodDoesNotExist();

// Methods.cpp
#include <string> // std::string
#include <istream> // std::istream
#include "Methods.h" // ::Methods_xxx

const std::string
method1( std::istream& stream_ )
    return "from method1";

const std::string
method2( std::istream& stream_ )
    return methodDoesNotExist();

// Tester.cpp
#include "Methods.h"
#include <fstream>
#include <iostream> // std::cout
#include <string>

int main(){
    std::ifstream stream;"testerParse.txt");

    std::cout << ::method1( stream ) << std::endl;

    char c;
    std::cin >> c;

Link Error:

------ Build started: Project: support library, Configuration: Debug
Win32 ------
Creating library...
Build log was saved at "file://c:\Test\BuildLog.htm"
support library - 0 error(s), 0 warning(s)
------ Build started: Project: testerParse, Configuration: Debug Win32
support library.lib(Methods.obj) : error LNK2019: unresolved external
symbol "class std::basic_string<char,struct
std::char_traits<char>,class std::allocator<char> > const __cdecl
methodDoesNotExist(void)" (?methodDoesNotExist@@YA?BV?$basic_string@DU?
$char_traits@D@std@@V?$allocator@D@2@@std@@XZ) referenced in function
"class std::basic_string<char,struct std::char_traits<char>,class
std::allocator<char> > const __cdecl method2(class
std::basic_istream<char,struct std::char_traits<char> > &)" (?
C:\Test\testerParse.exe : fatal error LNK1120: 1 unresolved externals
Build log was saved at "file://c:\Test\BuildLog.htm"
testerParse - 2 error(s), 0 warning(s)
========== Build: 1 succeeded, 1 failed, 0 up-to-date, 0 skipped

I am no expert at this, but I think you might take a look at

Function-Level Linking (/Gy switch in VC++)

David Wilkinson
Visual C++ MVP

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