Q123768: PRB: Unresolved Externals for Inline Functions
Article: Q123768
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,1.52,2.0,2.1,4.0,4.1,4.2,5.0,7.0
Operating System(s):
Keyword(s): kberrmsg kbCompiler kbCPPonly kbVC
Last Modified: 11-FEB-2002
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft C/C++ for MS-DOS, version 7.0
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0
-------------------------------------------------------------------------------
SYMPTOMS
========
Calling an inline function defined in a separate source file generates the
following errors in Visual C++ 32-bit Edition, versions 2.x and 4.0:
error LNK2001: unresolved external symbol "<function name>"
<filename.exe> : error LNK1120: 1 unresolved externals
The 32-bit edition of Visual C++ version 1.0 generates these errors:
warning LNK4016: unresolved external symbol
"<Classname>::<Functionname>"
error LNK1120: 1 unresolved externals
The 16-bit editions generate this error:
error L2029: '<ClassName>::<FunctionName>' : unresolved external
The function is declared in a header (.H) file, defined as an inline function in
one source (.CPP) file, and called from a second source (.CPP) file.
CAUSE
=====
Inline functions are not visible outside of the source file where they are
defined. The Inline Specifier section in the C++ Language Reference states,
"Functions that are declared as inline and that are not class member functions
have internal linkage unless otherwise specified."
The Inline Class Member Functions section in the C++ Language Reference states,
"A class member function defaults to external linkage unless a definition for
that function contains the inline specifier." Query on <inline function
linkage> in the Books On-line for further information.
RESOLUTION
==========
Here are five possible workarounds:
- Declare the inline function with the extern keyword to force external
linkage. Note, however, that using extern with class member functions will
cause a warning with /Ze, and an error with /Za.
-or-
- Move the function definition to the header file so it's included in each
translation unit used.
-or-
- Remove the inline specification.
-or-
- Force a function version of the inline function to be created in the module
that it is defined in. You can do this by referencing the address of the
inline function, by assigning it to a function pointer, or by passing it to a
function.
-or-
- Remove the /Ob1 (Only Inline) or /Ob2 (Any suitable) option from the command
line and compile with /Ob0 (Disable). The /Ob0 option is the default if no
options are specified.
To change these options from within the Visual Workbench for Visual C++
version 4.0, follow these five steps:
1. Select the Settings... option from the Build menu.
2. Select the C/C+ Tab in the Project Settings dialog box.
3. Select the Optimizations item in the Category drop-down list box.
4. Select one of the following items from the In-line function expansion
drop-down list box:
- Disable * (/Ob0)
- Only __inline (/Ob1)
- Any Suitable (/Ob2)
5. Press OK in the Project Settings dialog box.
To change these options from within the Visual Workbench for Visual C++
version 2.x, follow these five steps:
1. Select Project.
2. Choose Settings.
3. Change to the Settings for C/C++.
4. Select the Optimizing Category.
5. Choose the inline option from the Inline Function Expansion box.
To change these options from within previous versions of the Visual Workbench,
select Options and choose Project. Then choose Compiler. Change the Category
to Optimizations, and choose the inline option from the Inline Expansion of
Functions box.
STATUS
======
This behavior is by design.
MORE INFORMATION
================
Sample Code
-----------
/* Compile options needed: /Ob1 or /Ob2
*/
/* TEST.H */
class ClassA
{
private:
int Var;
public:
ClassA ();
~ClassA ();
};
/* TEST1.CPP */
#include "test.h"
void testfunc(void);
inline ClassA::ClassA() { Var = 6; }; // Inline function definition
ClassA::~ClassA() {}
void main(void) {
ClassA test1;
testfunc();
}
/* TEST2.CPP */
#include "test.h"
void testfunc(void)
{
ClassA test2; // This generates an unresolved external error
// on the default constructor when linked
}
Additional query words: 8.00 8.00c 9.00
======================================================================
Keywords : kberrmsg kbCompiler kbCPPonly kbVC
Technology : kbVCsearch kbVC400 kbAudDeveloper kbZNotKeyword8 kbvc150 kbvc100 kbZNotKeyword3 kbVC410 kbCVC700DOS kbVC420 kbVC500 kbVC151 kbVC200 kbVC210 kbVC32bitSearch kbVC16bitSearch kbVC152 kbVC500Search
Version : :1.0,1.5,1.51,1.52,2.0,2.1,4.0,4.1,4.2,5.0,7.0
Issue type : kbprb
=============================================================================
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 1986-2002.