Why does the compiler sometimes not give line number of the error? Where is the use case of that "undefined reference". I've already included everything as header files I myself wrote so it needs to give a specific line number. It is not closed source. Have I changed some setting of the compiler by accident or is it another thing whatever that another thing is?
D:\Projects\DanceOfPixels\GLEW>gcc main.c glad.c -IC:\mingw_dev_lib\include\SDL2 -LC:\mingw_dev_lib\lib -lmingw32 -lopengl32 -lSDL2main -lSDL2 -lSDL2_image -o main.exe -ansi -std=c89 -pedantic -w
C:\Users\user\AppData\Local\Temp\ccMooHZm.o:main.c:(.text+0x126ce): undefined reference to `drawImagePartScaledHW'
collect2.exe: error: ld returned 1 exit status
Edit: I have solved the problem. I have included two different versions of the draw.h, one coming from software renderer, other from OpenGL renderer. Since they use same
#ifndef DRAW_H
#define DRAW_H
...
#endif
structure for both files; the compiler didn't include the second. Once I've changed the DRAW_H to DRAW_HW I managed to compile and run the application.
That error comes from the "linker" (ld), not the compiler proper.
Typically, the compiler compiles each source file into its own, individual object file, containing just the code and data from that source file. Then, the linker combines one or more object files together, and also links in any needed library functions.
Crucially, there's no problem if a single source file (a single object file) calls an undefined function -- that's normal, if the definition of the function is in another source file, or a library. So that's why it's the linker (not the compiler) that finally discovers that there's not a definition for a function anywhere, that it's truly undefined.
But since the linker is working with object files, typically it doesn't know which source file line numbers the functions were originally called on.
(Some C compilers work more closely with their linkers, so that these "undefined external" error messages can, more usefully, contain actual source file line numbers, but that's a relatively recent innovation. For this to work it may be important to compile with debugging enabled, e.g. by using the -g flag, so that the compiler includes source line number information in its object files.)
Related
I am trying to create an executable with .o ,.so, .a files.
Here is my build command:-
pkgs/gcc/v4.8.3/bin/gcc -L/usr/X11R6/lib -O2 -DUSE_FLEX -Wall -Wno-char-subscripts -fPIC -DLINUX -DG_DISABLE_CONST_RETURNS -fno-strict-aliasing -o ../build/kl/Release/test/bin/pure.exe -L../build/kl/Release/test/modules ../build/kl/Release/test/maker/constrfunc.TCL.o ../../build/kl/Release/test/maker/pvdbprocs.TCL.o .. ../build/kl/Release/test/maker/maker/memmaker.TCL.o .. ../build/kl/Release/test/maker/modules/libdenbase.a .. ../build/kl/Release/test/maker/guibase.o -litk3.2 -litcl4.0.0 -ltk8.3 -lcdnviptcl8.4 -litclstub4.0.0 -ldenbase -lglib-2.0 -ldenbase -lX11 -ldl -lm -lviputil -lvippli -lcdsCommonMT_sh -lpthread -L/home/dlb/extlibs/arm/lib
I have libraries which have definitions of the functions at path "-L/home/dlb/extlibs/arm/lib" . Still it is throwing error below.
Error:
../build/kl/Release/test/maker/guibase.o: In function `decodeAddrList':
tree234.c:(.text+0xc): undefined reference to `ptritclStubsPtr'
tree234.c:(.text+0x20): undefined reference to `ptrlitclStubsPtr'
tree234.c:(.text+0x12c): undefined reference to `ptrlitclStubsPtr'
tree234.c:(.text+0x140): undefined reference to `ptrlitclStubsPtr'
I have the symbol in library which is at path /home/dlb/extlibs/arm/lib :-
Command:-
readelf -s libitcl4.0.0.so | grep ptrlitclStubsPtr
348: 0000000000060f10 8 OBJECT LOCAL DEFAULT 24 ptrlitclStubsPtr
Am I missing some thing here?
Note, OP has provided more info in a repost of the same question;
quote from comment by OP:
"Due to some privacy issues...I am renaming the symbols.. It was edited by me... It was typo...I just corrected it...:)"
I.e. the identifiers in the error message and the grep line and the output of the grep line have been manually altered.
It looks like the functions you're asking about are local to the file where they were defined. That is, it looks like they were explicitly intended not (and not even allowed) to be called externally.
That is, somewhere within the source for the shared library libitcl4.0.0.so probably appears a declaration like:
static tclStubs *ptrlitclStubsPtr;
That keyword static indicates that the visibility of the resulting symbol ptrlitclStubsPtr is confined to its own source file.
I infer all of this from the fact that your reported readelf output includes the line
348: 0000000000060f10 8 OBJECT LOCAL DEFAULT 24 ptrlitclStubsPtr
That flag LOCAL indicates that the symbol is local. If it were global, intended (and able) to be called externally, the flag GLOBAL would appear instead.
Why are variables made private (static) like this, so you can't use them? It's a software engineering thing, "information hiding", intended to reduce the "width" of the interface between you and a library like libitcl4. Symbols that are private are more intimately tied to the implementation decisions within libitcl4, decisions which are not supposed to be visible to, or any concern of, the callers. It's thought that, if callers were to have access to those symbols, callers would also have to know other implementation details, meaning that the author of libitcl4 would then be unable to change those implementation details without breaking (invalidating) the calling code. So to prevent that situation, the choice is usually made to make it impossible for the caller to become dependent in this way.
In this situation you basically have three paths forward:
Remove the static tags from the variable declarations in the sources to libitcl4.0.0.so. (This obviously requires that you have access to the sources to libitcl4.0.0.so, and the ability to rebuild it. It's also probably a very bad idea. As I've explained, those symbols were probably made static for a good reason.)
Add a new function within libitcl4.0.0.so which does whatever you need done, and which, by virtue of its placement within the same source file, does have access to those symbols. (This, too, requires that you have access to and the ability to rebuild ``libitcl4.0.0.so`.)
Find some other way of doing whatever you need done, using the existing public facilities of libitcl4.0.0.so.
I need to compile and, most importantly, link a C program that uses a proprietary function present in a shared library file. Because of lack of communication with the previous development team, there is no proper documentation. I declared a function prototype (because I know the number and type of arguments):
int CustomFunction(unsigned char *in, int size);
Since that function name can be grepped from /customlibs/libcustom.so, I tried to compile the code and link it like this:
gcc -L/customlibs testing.c -o testing -lcustom
Which throws a few error messages looking like this:
/customlibs/libcustom.so: undefined reference to `AnotherCustomFunction'
Obviously, I need to tell linker to include other libraries as well, and, to make things worse, they need to be in certain order. I tried exporting LD_LIBRARY_PATH, using -Wl,-rpath=, -Wl,--no-undefined and -Wl,--start-group. Is there an easy way to give the linker all the .so files without the proper order?
I found the solution (or a workaround) to my problem: adding -Wl,--warn-unresolved-symbols, which turns errors to warnings. Note that this works only if you are ABSOLUTELY certain your function does not depend on the symbols mentioned in undefined refernce to: messages.
Add them on the command line is a way to do it. Something like this below. The LD_LIBRARY_PATH tells gcc where to look for libraries, but you still need to say what libraries to include.
gcc -L/customlibs testing.c -o testing -lcustom -lmylib1 -lmylib2 -lmylib3
You should also include all the header files of your shared library by adding the -I option of gcc, for example : gcc [...] -I/path/to/your/lib/header/files [...]
Now I am writing a program to call a web service. I write testMain.c. The others are generated by wsdl2h and soapcpp2.
My compiling command is like this:
gcc -Wall -g -c -L. soapC.c soapClient.c stdsoap2.c testMain.c
gcc -o testMain -L/usr/lib -lgsoap -lgsoapck -lgsoapssl soapC.o soapClient.o stdsoap2.o testMain.o
And I get these errors. Please help me.
stdsoap2.o: In function `soap_print_fault':
/test/stdsoap2.c:16279: undefined reference to `soap_check_faultsubcode'
/test/stdsoap2.c:16281: undefined reference to `soap_check_faultdetail'
stdsoap2.o: In function `soap_sprint_fault':
/test/stdsoap2.c:16341: undefined reference to `soap_check_faultdetail'
collect2: ld returned 1 exit status
Recent versions of GCC/ld/the GNU toolchain require that the object and library files be specified in a certain order, so that symbols can be found by the linker in the same order they depend on each other. This means that libraries should go to the end of the command line; your second line (when you're linking) should be
gcc -o testMain -L/usr/lib soapC.o soapClient.o stdsoap2.o testMain.o -lgsoap -lgsoapck -lgsoapssl
instead.
I search the web, and found a post which is very similar with my problem. I use this solution and have solved the problem. http://www.mail-archive.com/gsoap#yahoogroups.com/msg01022.html
You should not need to link stdsoap2.o to your project because it's already included in libgsoap (given through the gcc linker option -lgsoap). Try to exclude stdsoap2.c from your project. From the gSOAP FAQ:
I get a link error with gcc/g++ (GNU GCC). What should I do? For C
apps: use soapcpp2 option -c to generate C code, use only the
package's .c files, link with libgsoap.a (-lgsoap) or use the lib's
source stdsoap2.c (and dom.c when applicable).
I had the same problem with gsoap-2.8.16 compiled from source. (That version was shipped with CentOS 6.)
First I checked for a missing library. According to nm used on all static libraries provided by gsoap-2.8.16:
for X in /usr/local/lib/libgsoap*.a ; do echo $X; nm $X | grep soap_check_faultdetail; done`
it turned out that none of the libraries provided the missing symbols.
A brief look at the source code revealed that the expected return type of both methods soap_check_faultdetail and soap_check_faultsubcode was const char*, and that these were used to generate error messages.
It looked to me as if these are meant to be callbacks that the client must provide. Maybe their implementation is WSDL-dependent and would be supplied by the gsoap code generation utilities - that I don't know, see the answer from #ChristianAmmer above or below.
Anyway, since I knew the symbols were nowhere supplied, and that null-terminated strings were probably acceptable here, I just supplied my own no-op implementation:
// gsoap-missing-symbols.cpp
extern "C" {
const char* soap_check_faultdetail() { return 0; }
const char* soap_check_faultsubcode() { return 0; }
}
This is a brute-force solution. If you follow this solution, you should maybe check for linker warnings in the future; maybe some mechanism (eg. from the gsoap code generator) will supply conflicting implementations later during development.
For later versions of gsoap, I believe these symbols are no longer used and can be dropped (or renamed), see soap_check_faultX in https://www.genivia.com/changelog.html.
I am trying to compile a program written in c using the expect.h header. I am trying this:
cc -I/usr/include main.c -lexpect -ltcl
cc -I/usr/include main.c
I tried the same with gcc, but to no avail.
I get this:
undefined reference to `exp_spawnl'
undefined reference to `exp_expectl'
Any ideas?
Thanks,
Walter
It means that regardless of what you thought was being used, the expect library being used does not contain those two functions. So, you need to track down which expect library is actually loaded, and then check whether the functions are in it (they aren't, but you should check to see what is defined).
Once you've found your library, you can use nm -g libexpect.so to see the symbols defined. I would expect that you will not see exp_spawnl or exp_expectl in the list of defined symbols.
Then you need to find out which version of the library you do have, and decide whether to upgrade, etc.
I am assuming that the names you quote are indeed spelled correctly.
Is the expect header file installed in /usr/include?
I think the undefined reference error comes from the linker and not the compiler. What directory is the library installed to? Try to link against it using the
-L/path/to/lib -lexpect
option
I'm trying to compile the Neko VM on Mac OS X (10.5.7) using GCC 4.01 and I'm completely stuck, because it stops while compiling saying:
vm/threads.c:202: error: conflicting types for 'neko_thread_register'
vm/neko_vm.h:37: error: previous declaration of 'neko_thread_register' was here
I've tried googling this and some say it's because of lack of a "prototype" and some say it's because of a header include being done several times, and I can't really find any of those.
The affected line in threads.c:202 looks like this:
EXTERN bool neko_thread_register( bool t ) {
And the affected line in neko_vm.h:37 looks like this:
EXTERN bool neko_thread_register( bool t );
I can't see any difference in them, besides one of them being the implementation of the other.
The compiler command I'm using is:
cc -Wall -O3 -v -fPIC -fomit-frame-pointer -I vm -D_GNU_SOURCE -arch i386 -L/usr/local/lib -L/opt/local/lib -I/opt/local/include -o vm/threads.o -c vm/threads.c
I'd appreciate some ideas on what i might be able to do here, I don't really know where to go from here.
A mirror of the code for Neko which I'm trying to compile can be found here.
Thanks!
Have you tried compiling that file alone and outputting the preprocessed version? It could be that the scope or linkage macros are being modified somewhere in between the header file and the implementation file-- the same could be true of the 'bool' type, which is usually a macro defined by a system header.
According to the GCC 4.2 docs here, you should need to add the -E flag to the compilation line above, and you ought to change -o vm/threads.o to -o vm/threads.i so a file with the correct extension is created (.i means 'preprocessed file', essentially).
First, make sure you compile this as C, not C++.
Second, without seeing the code, it's pretty much impossible to say what the problem is.
But reading the error messages is often helpful (even before you google them):
Apparently neko_thread_register is declared twice, once in threads.c:202 and once in neko_vm.h:37, and the two declarations have different (conflicting) types. So look at the two declarations. If you can't see a problem with them, show us some code.
At the very least, seeing those two lines of code would be necessary. Most likely, the types are typedefs or macros or something similar, and then we'd need to see where they are defined as well.
Without seeing the code, all we can do is repeat the compiler error. "neko_thread_register has two conflicting definitions, at the lines specified."
Did you uncomment this line:
# For OSX
#
# MACOSX = 1 <-- this one
In the makefile?