C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  C++ noob - compiler question.          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Sheppe Guest Posted: Tue Aug 24, 2004 10:51 pm    Post subject: C++ noob - compiler question. I'm not new to programming, but I am fairly new to C++. I've got a bit of a problem with a project that I am working on. My environment is as follows: OS: Mandrake 10 IDE: Anjuta Compiler: gnu The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? Thanks. -Sheppe [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Raoul Gough Guest Posted: Wed Aug 25, 2004 11:36 am    Post subject: Re: C++ noob - compiler question. Sheppe <noone (AT) nowhere (DOT) com> writes: [snip] Quote: The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? Probably a linkage specification problem. C++ compilers generally use name "mangling" to provide type-safe linkage, so the (C++) function declaration extern void function_name_here(int, int); will actually produce a symbol for the linker like __Z18function_name_hereii (this is what g++ 3.3.1 actually produces, other compilers may use a different scheme). A plain old C function with the same prototype will produce a non-mangled symbol like _function_name_here. The linker won't be able to match these symbols for the obvious reason. Because of this, if you want to use a C function from within C++, you have to notify the C++ compiler, by declaring the function like this: extern "C" void function_name_here (int, int); Typically, header files (probably including most everything in /usr/include on your system) that are compatible with C and C++ do this: #ifdef __cplusplus extern "C" { // Enclose all of the rest in this linkage spec #endif /* C and C++ compatible stuff */ #ifdef __cplusplus } #endif Actually, the name mangling is just a common implementation detail, and there may be other reasons why you need to tell the compiler that it's a plain C function (e.g. calling conventions may differ). -- Raoul Gough. export LESS='-X' [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Frédéric Lachasse Guest Posted: Wed Aug 25, 2004 11:38 am    Post subject: Re: C++ noob - compiler question. "Sheppe" <noone (AT) nowhere (DOT) com> wrote Quote: I'm not new to programming, but I am fairly new to C++. I've got a bit of a problem with a project that I am working on. My environment is as follows: OS: Mandrake 10 IDE: Anjuta Compiler: gnu The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? You need to put the C definitions in the C++ program inside an extern "C" block, for example, if the definitions are in a header cdefs.h: extern "C" { #include "cdefs.h" } If you want to understand why, look for extern "C" and name mangling in C++ documentation. -- Frédéric Lachasse - ECP86 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Mooney Guest Posted: Wed Aug 25, 2004 11:41 am    Post subject: Re: C++ noob - compiler question. Sheppe wrote: <snip> Quote: The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? The "undefined reference" message is from your linker. The compiler is responsible for translating your source code into object modules. The linker is responsible for knitting object modules (yours and others) into an executable. Somewhere (likely in a header (.h) file) you have _declared_ a function: void function_name_here(...); Somewhere else you have invoked that function through a call. The format of the call matches the prototype, so the compiler is happy. It generates an external reference for the linker to resolve. Unfortunately, you haven't _defined_ the function (you haven't supplied that actual function with a body (typically in a .cpp file)). So you've broken the promise you've made in the header file. Supply the promised function and all should be well. (Well the linker should stop complaining anyway. <g>) -- TFM3 Note: Spam-resistant e-mail address [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top David B. Held Guest Posted: Wed Aug 25, 2004 11:42 am    Post subject: Re: C++ noob - compiler question. Sheppe wrote: Quote: [...] The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? Because compiling only checks the translation units in question. It does not resolve external references. That's the job of the linker. When you build the project, the linker gets invoked, and finds that some functions that you refer to in your source files don't have a definition anywhere in your project. You probably need to add the correct object/source files to your project so that the linker can see all the definitions that it is looking for. So you might have a file called file1.cpp that refers to a function called foo() located in file2.c. You either want to add file2.c to your project, or you want to add file2.o to your project. Another alternative is if file2.o is in a library called lib2.a. Then you want to add that library to your project so the linker knows to search it. Dave [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Nathan Guest Posted: Wed Aug 25, 2004 11:43 am    Post subject: Re: C++ noob - compiler question. Sheppe wrote: Quote: The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? From what I can determine is that you are not compiling and then linking the file with the C functions. The easiest way to do this is to create a Makefile, and then use the command "make" to compile your project. Here are some sites I got from a quick search on Google for some Makefile tutorials: http://www.groovyweb.uklinux.net/index.php?page_name=how%20to%20write%20a%20makefile http://vergil.chemistry.gatech.edu/resources/programming/c-tutorial/make.html http://sources.redhat.com/autobook/autobook/autobook_toc.html http://www.psc.edu/~welling/33-456/notes/GNUmakeTutorial.html If this is not the problem you are having, are you protoyping your functions? In the file with the Class, do you have a list of the functions you plan to use? i.e: // File: myclass.cpp void callCFunction(); // This is some function from your file // containing the C functions. [ ... ] void someclass::dosomething() { [ ... ] callCFunction(); } Well, I hope this helps! Nathan [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Conrad S. Guest Posted: Wed Aug 25, 2004 11:49 am    Post subject: Re: C++ noob - compiler question. "Sheppe" <noone (AT) nowhere (DOT) com> schreef in bericht news:KyLWc.208944$gE.192331 (AT) pd7tw3no (DOT) .. Quote: I'm not new to programming, but I am fairly new to C++. I've got a bit of a problem with a project that I am working on. My environment is as follows: OS: Mandrake 10 IDE: Anjuta Compiler: gnu The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? Thanks. -Sheppe When you compile a file you translate _only_ one C or CPP file (including any include files) into a single object file.Calls to functions in other files (your C functions) are not resolved yet; the compiler doesn't know about their existance just accepts that they do on good faith. Now when you build your project, all these object files are linked together to make an executable. For this all references which the compiler accepted on good faith must now be resolved. That is if you called function ThisIsNifty() in file MyClass.cpp (which has been compiled into MyClass.obj), the linker will search all other object files to find which one contains ThisIsNifty(). If the linker fails in its quest it gives up and tells you it can not do what you want it to do. Looking up a name might seem straightforward but when you throw in C++ it is not. To allow function overloading C++ does a little trick called name mangling: the compler actualy changes the name of your function to something else. Thus when you think you are calling "int ThisIsNifty( int )" from your cpp file you end up calling @@int@ThisIsNifty@@int or something similarly weird. So what probably happened in your case is that the linker could not match up the names in your C++ part with the ones in your C part. As it is not uncommen what you are trying to do, the C++ language allows you to explicitely turn of name mangling by wrapping part of the code like this: extern ("C") { } Antoon [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Ulrich Eckhardt Guest Posted: Wed Aug 25, 2004 8:50 pm    Post subject: Re: C++ noob - compiler question. Sheppe wrote: Quote: The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. Firstly, these errors are linker errors, not compiler errors. 'undefined reference' means that something you promised to provide is not there. Another common one is 'multiple definition' which means there are too many of some thing. In your case, I guess it is related to the difference between a C function prototype and a C++ function declaration. The line void function( char*); declares a function, but differently for both languagues. In order to access C functions in c++, you have to either prefix them like this: extern "C" void function( char*); or, more convenient when dealing with a whole bunch of them like this: extern "C" { void function( char*); void another_function( char*); } However, C doesn't know these extern statements, which is why you need to hide them in order to share headers: #ifdef __cplusplus extern "C" { #endif void function( char*); void another_function( char*); #ifdef __cplusplus } #endif HTH Uli -- FAQ: http://parashift.com/c++-faq-lite/ /* bittersweet C++ */ default: break; [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Timo Geusch Guest Posted: Wed Aug 25, 2004 8:55 pm    Post subject: Re: C++ noob - compiler question. Sheppe was seen penning the following ode to ... whatever: Quote: I'm not new to programming, but I am fairly new to C++. I've got a bit of a problem with a project that I am working on. My environment is as follows: OS: Mandrake 10 IDE: Anjuta Compiler: gnu The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm not familiar with that particular IDE - when you say 'build' as opposed to compile, I assume that your IDE is attempting to link the object files generated by the compile stage, correct? Did you compile the 'C' file as well? Are you trying to link both into the same executable? If that's the case, did you #include the C header marked as 'extern "C"' so the compiler knows to turn off the C++ name mangling for these particular prototypes? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Mike Capp Guest Posted: Wed Aug 25, 2004 9:43 pm    Post subject: Re: C++ noob - compiler question. Sheppe <noone (AT) nowhere (DOT) com> wrote Quote: The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I don't know Anjuta, but I presume that "Build" is trying to link the project as well as compile it, and I suspect that you're missing an extern "C" around the header declarations of your C functions. C doesn't have overloading, so parameters aren't part of the function's name as seen by the linker. C++ does have overloading, so they *are* part of the "mangled" linker name. In short, your C++ compiler is seeing a call to foo(int), thinking it's a C++ function and telling the linker that it'll need to link to a function called "foo@int" or somesuch. Your C compiler is compiling the definition of foo(int), thinking it's a C function and telling the linker about a function called "foo". The two names don't match up, hence your problem. Look up 'extern "C"' in any C++ reference; it should tell you all you need to know. cheers, Mike [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Sheppe Guest Posted: Fri Aug 27, 2004 3:10 am    Post subject: Re: C++ noob - compiler question. Thanks for all the respons It ended up being that I had to include the extern "C" lines. Cheers, -Sheppe "Sheppe" <noone (AT) nowhere (DOT) com> wrote Quote: I'm not new to programming, but I am fairly new to C++. I've got a bit of a problem with a project that I am working on. My environment is as follows: OS: Mandrake 10 IDE: Anjuta Compiler: gnu The project I am working on is a C/C++ combo. I've created a class (in C++) to encapsulate a particular bit of functionality; this class makes calls to some C functions in a separate file (nothing complicated). All of the necessary includes are in place. The problem is this: when I "Compile" my file, it works fine and produces no errors, but when I go to "Build" my file I get errors in the file that I just compiled with no errors. The errors read "undefined reference to function_name_here(param1*, param2)". The errors are produced on each line that makes a call to a function in the C file. I'm a little confused as to what I need to do here. Why does it compile but not build? Thanks. -Sheppe [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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