Category : C++ Source Code
Archive   : C_ALL.ZIP
Filename : TI864.ASC

PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 1/11

TITLE : Understanding "Undefined Symbol" Error Messages.




One of the most common error messages seen by developers using a
C or C++ compiler is "undefined symbol." This document provides
a general description of what causes undefined symbol error
messages, as well as instructions on solving specific undefined
symbol errors.


UNDEFINED SYMBOL AT COMPILE TIME
An undefined symbol at compile time indicates that the named
identifier was used in the named source file, but had no
definition in the source file. This is usually caused by a
misspelled identifier name, or missing declaration of the
identifier used.

EXAMPLE 1:
int main(void)
{
test = 1;
return 0;
}

The code shown for example one will cause an undefined
symbol error message to be displayed becuase the variable
"test" has not been declared in either a header file which
has been included or in the actual code itself.

EXAMPLE 2:
int main(void)
{
int test;
Test = 1;
return 0;
}

The code shown for example one will cause an undefined
symbol error message to be displayed because when the
variable "test" was used it was misspelled. The misspelling
was a capital 't' instead of a lower case 't'.

EXAMPLE 3:
int main(void)
{
int test;













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 2/11

TITLE : Understanding "Undefined Symbol" Error Messages.




test = 1;
return 0;
}

The code shown in example three has no errors and is an
example of what must be done to resolve an undefined symbol
error message. In the example here we simply made sure we
have a definition for the integer test and that we spelled
it the same at the time we used it. It's that simple!


UNDEFINED SYMBOL AT LINK TIME
When linking multi-file projects, the linker must resolve
all references to functions and global variables shared
between modules. When these references cannot be resolved,
the linker generates an "undefined symbol" error message.
This means that after searching all of the object files and
libraries which are included in the link, the linker was
unable to find a declartion for the identifier you were
using. This can be caused by:

forgetting to include a needed object module or library
in your link (project file, response file, or command
line).

misspelling the name of the undefined symbol either
where it was used or where it was declared.

in the case of global variables, all may have been
declared "extern".

mixing C++ with C or Assembly modules, you may have
forgotten to use extern "C" to disable name mangling.
See the specific entry on this subject elsewhere in
this document or consult the helpme!.doc file included
with the product.

one of your modules may have Generate Underbars turned
OFF.

If all else fails, TDUMP.EXE both object modules and note
any difference between symbols. This will usually trigger
an insight sufficient to resolve the problem. For specific













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 3/11

TITLE : Understanding "Undefined Symbol" Error Messages.




information on using TDUMP.EXE, please consult the
documentation included with the product.


COMMON UNDEFINED SYMBOL ERRORS
The following list provides solutions to some of the more
common causes of undefined symbol errors:

UNDEFINED SYMBOL WHEN TLINKING FROM DOS COMMAND LINE
The TLINK command line must have the libraries in the
following order ( GRAPHICS.LIB + + EMU.LIB
+ MATH (S,T,C,M,L - for model) + C (S,T,C,M,L - for
model)

UNDEFINED SYMBOL LINKING C/C++ AND ASSEMBLY MODULES
There are several sources of undefined symbol errors
when trying to link assembly with C or C++ modules:

The Turbo Assembler generates all uppercase
symbols unless you specify /ml or /mx on the
assembly command line. Since C modules are, by
default, case sensitive, failing to do this will
result in undefined symbols for all symbols that
are not completely upper case in the C module(s).

The symbols in the assembly file being referenced
from a C module must be declared using a PUBLIC
directive. TLINK will not consider symbols that
are not declared PUBLIC in an attempt to resolve
and undefined symbol consition.

All symbols in the assembly module that are
referenced in the C module must be
prototyped/declared as extern in the C module
otherwise the compiler will generate undefined
symbol errors for such symbols.

All symbols in the assembly module that will be
referenced from a C module must have a underscore
prefix. This naming convention must be used in
the assembly module. You can do this explicitly
(_symbol) or you can use:














PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 4/11

TITLE : Understanding "Undefined Symbol" Error Messages.




.model , C

to specify this implicitly for all symbols.

IMPORTANT NOTE: If you put underscores in front of
your assembly routines and also specify the

.model , C

directive, however, the public symbol will be
generated with two underscores; consequently an
undefined symbol error will be generated.

If all else fails, TDUMP both object modules and note
any difference between symbols. This will usually
trigger an insight sufficient to resolve the problem.
For specific information on using TDUMP.EXE, please
consult the documentation included with the product.


UNDEFINED SYMBOL LINKING C++ WITH C OR ASSEMBLY MODULES
C++ is a strongly typed language. In order to support
type-safe linkage (as well as function overloading),
Borland C++ must attach information to the symbols
generated for function names and variables. When this
is done, the symbol will no longer match the standard C
style function name. In order to link correctly with C
or assembly modules, the compiler must be notified that
the symbol is to be in the standard C style (non-
encoded) rather than employing C++ name-mangling
(encoded). This is done by prototyping the function as
type extern "C". Here is a quick example:

extern "C" int normal_c_func( float, int, char );

For an additional example, you may want to look at the
header files which came with the product. One such
header file is stdio.h.

UNDEFINED SYMBOL: '_main' IN MODULE C0.ASM
Every C program must contain a function called main().
This is the first function executed in your program.
The function name must be all in lower case. If your













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 5/11

TITLE : Understanding "Undefined Symbol" Error Messages.




program does not have one, create one. If you are using
multiple source files, the file that contains the
function main() must be one of the files listed in the
Project.

Note that an underscore character '_' is prepended to
all external Turbo C++ symbols.

In addition to an absent, misspelled or mis-cased
symbol main, there are two additional common causes:

The "generate underbars" option is disabled.

The Pascal calling Convention rather than the C
calling convention is selected.


UNDEFINED SYMBOL: A PSEUDO REGISTER (ie. _AX)
Pseudo registers are only allowed in the Turbo C++ and
ANSI modes of the compiler. You can change this setting
in the Options | Compiler | Source menu.


UNDEFINED SYMBOL: 'FIWRQQ'
Your program uses floating point routines directly (or
indirectly) and you have NONE selected for floating
point. OR, you are using TLINK and have forgotten to
include EMU.LIB or FP87.LIB on the command line.


UNDEFINED SYMBOL: AN IOSTREAM CLASS MEMBER
If you are using the Integrated Development Enviroment
simply turn off Options | Compiler | Code Generation |
Unsigned Characters.

If you are using the command line compiler simply
remove the '-K' option.


UNDEFINED SYMBOL: 'abort()'
The sole purpose of abort is to print the error message

"Abnormal Program Termination"













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 6/11

TITLE : Understanding "Undefined Symbol" Error Messages.




and exit the program with an error code of 3. This
function is located in the startup code C0.ASM. Linker
errors indicating that abort() is an undefined symbol
are only possible if the standard startup code is not
being linked into a project. Although this is not
common is routine C/C++ development exercises, it is to
be expected when linking in code written other
languages such Microsoft Fortran, and Clipper and in
cases where embedded systems are being developed.

To resolve the undefined symbol, extract the abort()
function from the startup code and make a separate
object out of it to be linked into the project.


UNDEFINED SYMBOL: '_exitclean()'
There is a function called _exitclean which is new to
Turbo C++. Users moving from Turbo C 2.0 to Turbo C++
may encounter _exitclean() as an undefined symbol at
link time. _exitclean() is defined in the Turbo C++
startup code. Users creating embedded system (rommable
code), who do not use the standard Turbo C++ startup
code, are likely to encounter _exitclean() as an
undefined symbol. These users can strip the function
from the C0.ASM file and create a separate .OBJ file
which can be linked. Another option would be to
purchase the TC++ RTL source and make the necessary
adjustments.


UNDEFINED SYMBOL: LLSH or SCOPY or FMUL or FDIV
The helper functions have changed their names from
Turbo C 2.0 to Turbo C++. This can lead to many
undefined symbol issues.

When LLSH or SCOPY or FMUL or FDIV (note no underscores
here) appear as undefined symbols at link time, it is
likely that an object module or library has code
generated a call to some helper function from the
Turbo C 2.0 libraries. The solution is to simply
recompile all objects from source. You can do this by
choosing Comple | BuildAll from the menu in the
Integrated Development Environment.













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 7/11

TITLE : Understanding "Undefined Symbol" Error Messages.




UNDEFINED SYMBOL: STATIC POINTER TO A CLASS MEMBER FUNCTION
Any static member of a class must be initialized
otherwise that static member generates an undefined
symbol error. The following is an example of how to
initialize a static pointer to class member function of
a class is initialized:

// When testing static member initialization, you must
// declare an instance of the class in a main function;
// otherwise, the linker has no reference which it must
// try to resolve, and the undefined symbol error will
// not be seen - thus you won't know that your
// initialization was in error.

#include

// used to allow global initialization of static member
// pointer
typedef void (*fptr)();

// declare class containing static members
class First
{
public:
static fptr statptr;
};

// initialize static members of class First
fptr First::statptr = NULL;

int main(void)
{
First fVar;

if (fVar.statptr == NULL)
cout << "fVar.statptr is NULL: " <<
fVar.statptr << endl;

return 0;
} // end of main()


UNDEFINED SYMBOLS WHEN LINKING WHELLO.CPP













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 8/11

TITLE : Understanding "Undefined Symbol" Error Messages.




Undefined symbol messages when linking WHELLO.CPP are
generated when TLINK 3.0 is used rather than 4.0 or
5.0. To resolve this problem insure that you are using
the latest version of TLINK that was included with the
product.


UNDEFINED SYMBOL IN "USER INTERFACES IN TURBO C++" DEMO
The demo that accompanies the book "Graphic User
Interfaces for Turbo C++" compiles fine under Turbo C++
but will not compile Borland C++; undefined symbols
error messages are generated link for three member
functions defined in the PianoPage class.

There is a difference between how TC++ and BC++
implement the C++ specification. BC++ 2.0 requires
that you define the static member variables at file
scope. That is, outside any function or class, you
need a line like:

int PianoPage::recorder_mode = 0;

and similarly for the other two statics.


UNDEFINED SYMBOL: '_WSPRINTF'
Turn off the "Case-sensitive exports" and "Case-
sensitive link" options. If you are using the command
linker, don't use the /c switch. If you are invoking
the linker from the BCC(x) command line, use the -lc-
switch. If you are using the IDE, go to the linker
options dialog box and turn off the case sensitivity
switch.

UNDEFINED SYMBOL: 'fidrqq'
You will get undefined symbol fidrqq when using the
Integrated Development Environment if you have the
Options | Compiler | Code Generation | More |
Floating Point Option set to NONE and you are using
floating point arithmetic in your program. In order to
best solve this problem you must set the IDE option for
Floating Point to either the emulation choice or to the
80x87 choice. Note that if you choose an 80x87 setting














PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 9/11

TITLE : Understanding "Undefined Symbol" Error Messages.




the application generated by the compiler will require
an 80x87 chip to be present at runtime. Use this
setting only when truly appropriate.


UNDEFINED SYMBOL IN WINDOWS.H
Make sure you are using the windows.h file that came
with Borland C++, NOT the windows.h that came with the
Microsoft Windows SDK. If you include the Microsoft
windows.h file you will get many undefined symbols
including WINMAIN in caps and translatemessage in lower
case. Use our windows.h file instead of Microsoft's
when you are using our compiler.


UNDEFINED SYMBOL USING TCLASDLL.LIB
To use the DLL version of the container class library
you must do ALL of the following:

use the large memory model

use Smart Callbacks

turn case sensitive link ON

turn case sensitive exports ON

use the DLL version of the RTL

define _CLASSDLL


UNDEFINED SYMBOL USING SELECTORS PROVIDED BY WINDOWS
If you are using _C000h or other selectors provided by
Windows and they are coming up as undefined symbols,
perhaps you are compiling in C++ mode and forgot to
extern "C" them.

Programming in C:
extern WORD _C000h

Programming in C++:
extern "C" WORD _C000h













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 10/11

TITLE : Understanding "Undefined Symbol" Error Messages.




UNDEFINED SYMBOL: 'ChangeSelector'
The Windows API function ChangeSelector() has the wrong
name in KERNEL.EXE for Windows 3.0, and therefore in
IMPORT.LIB. The name given to this function (this is
NOT a joke) is PrestoChangoSelector().

Use PrestoChangoSelector() in your program in place of
ChangeSelector() and all will be well.


UNDEFINED SYMBOLS USING THE OBJECTWINDOWS LIBRARY (OWL)
If you get the undefined symbols

TApplication(unsigned char far *, unsigned int,
unsingned int, unsigned char far *, int )

and

TWindow::TWindow(TWindowsObject near *, unsinged
char far *, TModule near *)

when linking an OWL application it could be because you
have forced unsigned characters. The functions in the
.lib take signed characters and thus if you compile to
use unsigned characters, the symbols will not match.

Using the Integrated Development Environment be sure to
turn off Options | Compiler | Code Generation |
Unsigned Characters.

If you are using the command line compiler be sure to
remove the -K option to solve this problem.


UNDEFINED SYMBOL: 'Object::new(unsigned int)'
You forgot to link with the TCLASDLL.LIB file where it
is defined!

Basically the problem is that you are mixing both
STATIC and DYNAMIC LINK libraries into the application.
You must use only one or the other. If you are working
in the IDE, change the LINKER options section for
libraries.













PRODUCT : Borland C++ NUMBER : 864
VERSION : ANY
OS : NA
DATE : August 12, 1992 PAGE : 11/11

TITLE : Understanding "Undefined Symbol" Error Messages.




If you are using the command line compiler and linker,
just be sure to specify the correct set of library
files. For specific information on the "correct set of
library files" please see the documentation included
with the product as library names tend to change from
version to version.

DISCLAIMER: You have the right to use this technical information
subject to the terms of the No-Nonsense License Statement that
you received with the Borland product to which this information
pertains.