I have read this question: How do you USE Fortran 90 module data
But I could not solve my problem.
I get error LNK2019: unresolved external symbol when I try to use a variable which is declared in another module.
For background information: I am a beginner in Fortran and am working in a project someone else has created. I am using an Intel fortran composer and visual studio. I do not know for sure if I understand the use of public and private module data properly.
The problem is whenever I try to use the variable BodySystem in another module, it doesn't work and I get the error that there is an unresolved external symbol.
Am I using the public and private parts incorrect or am I missing something else?
Edit: I changed the code into a compilable snippet
Edit2: Deleted the code, since that was not the problem. IanH gave me the right answer as the object file was out of date.
The exact error message I get is:
Error 2 fatal error LNK1120: 1 unresolved externals Debug\HmSlam.exe
Error 1 error LNK2019: unresolved external symbol _COORDINATESSYSTEM_M_mp_BODYSYSTEM referenced in function _MAIN__ HmSlam.obj
where HmSlam is the main program and coordinatessystem_m is the module where the variable bodysystem is declared.
The "mangling" of the missing symbol in the linker error message tells you that the compiler knows that the name BODYSYSTEM comes from the module COORDINATESSYSTEM_M, otherwise it wouldn't have been able to mangle the module name and the symbol name together in the way that it has (compilers will have different name mangling conventions).
That tells you that the problem is probably not with the compiling of your code - something is going wrong in the linking stage.
I suspect you are providing out-of-date object files to the linker, or you are not providing the relevant object file at all.
(While we are here:
The use of type bound procedures means that this isn't Fortran 90 - it is at least Fortran 2003. Welcome to the 21st century.
You don't have a private and public "part" to your source - what you have are private and public statements. The PRIVATE keyword on its own in a statement indicates that the default accessibility for the module is private - i.e. by default the things defined or declared in the module won't be made available in places where the module is USE'd. Without such a private statement the default for a module is public. The PUBLIC keyword followed by a list of identifiers then specifies that those identifiers are public (contrary to the default set by private). The general positioning and number of the private and public statements isn't significant, as long as they appear in the specification part of the module, after any use and implicit statements.
naming an identifier in the ONLY specifier of a USE statement doesn't "call" anything, it just says "only this symbol (along with any others listed in the specifier) are available from this module for use in the following scope".
Related
So, I have problem, when try to use any of static members of SFML Library like sf::RenderState::Default or sf::Color::Blue.
error LNK2001: unresolved external symbol "public: static class sf::RenderStates const sf::RenderStates::Default" (?Default#RenderStates#sf##2V12#B)
But when I comment lines, I have access to sf::window (it be created, but can't draw anything, because sf::Drawble has sf::RenderState::Default as standart argument).
I checked everything including linker and compiler in Solution properties in Visual Studio (I have VS19).
P.S. I use the latest version of SFML (2.5.1) and Visual C++20.
Thanks for your help.
The troubleshooting steps I would undertake in this situation go from easiest to the inverse of that.
If I check the declaration of sf::RenderState::Default, can it be found?
If I create a new project with just this feature used, does the error persist?
If I redo my linking and directory searches, is the problem fixed?
Do I have a version compatible with my compiler?
Furthermore, the amount of information you've given about your environment is not enough to speculate on what the issue could be. It might be helpful to post your version of SFML, your compiler (and kind), what your project is like (shorthand.)
SFML can be compiled from source if necessary. Sometimes, using an incompatible version on accident will not show any issues on many basic things until you run into weird errors.
See this document on compiling SFML from source:
https://www.sfml-dev.org/tutorials/2.5/compile-with-cmake.php
So, thanks for AlixianaBritmonkey, I managed with this problem. I just create new project and moved every file. I don't know why problem occured before, but my solution helped.
I am working on a project of boost unit testing framework using QT creator. I have written a small test program and trying to link libboost_unit_test_framework-vc100-mt-gd-1_56.lib. This library is present at specified path. But program fails to compile giving said linking error.
I searched on net and found that, error should go with #define BOOST_ALL_NO_LIB. But then, I am getting below error:
main.obj:-1: error: LNK2019: unresolved external symbol "class boost::unit_test::test_suite * __cdecl init_unit_test_suite(int,char * * const)" (?init_unit_test_suite##YAPAVtest_suite#unit_test#boost##HQAPAD#Z) referenced in function _main
The above function is a part of libboost_unit_test_framework-vc100-mt-gd-1_56.lib.
I have written same unit tests using VS 2010 and with the same boost libraries. The program worked properly with expected behavior.
What could be possibly going wrong with the usage of boost on QT?
You are missing the test module initialization function. Have you defined BOOST_TEST_MAIN or BOOST_TEST_MODULE before you include the UTF header?
To automatically generate an empty test module initialization function you need to define BOOST_TEST_MAIN before including the boost/test/unit_test.hpp header. The value of this define is ignored. Alternatively you can define the macro BOOST_TEST_MODULE to be equal to any string (not necessarily in quotes). This macro causes the same result as BOOST_TEST_MAIN, and in addition the macro value becomes the name of the master test suite.
For a test module consisting of multiple source files you have to define these flags in a single test file only. Otherwise you end up with multiple instances of the initialization function.
More info here: http://www.boost.org/doc/libs/1_57_0/libs/test/doc/html/utf/user-guide/initialization.html
I am trying to diagnose linker/runtime errors using setenv LD_BIND_NOW TRUE. When I run the executable with this option enabled, I get the error
lib/libmkl_intel_thread.so: error: symbol lookup error: undefined symbol: DftiFreeDescriptor (fatal)
However, if I then remove the LD_BIND_NOW environmental variable, the program executes just fine (until termination, whereupon it reports a memory corruption--though that might be unrelated).
So I am a bit confused: How does the program execute when it has a symbol lookup error? I thought it would have to terminate as the program is written in C++, not Java. (See here for reference.)
Also, does this error imply that my rpath is set incorrectly, or has the MKL so been built improperly? Is there a fix that can be achieved in bounded time?
Firstly, I thought you needed LD_BIND_NOW=1 (as opposed to TRUE, though that may be a synonym).
Secondly, although your application would not have linked had there been an unresolved symbol, is it possible you've done some form of shared library update so that one of the libraries used now uses a library in turn with an unresolved symbol? Or that it's using a different library to that with which it was linked?
I am attempting to build a project in Visual Studio 2012 that uses GnuTLS. I downloaded the latest official Windows build from the website, and created a link library by running lib /def:libgnutls-28.def in the bin directory form a Visual Studio command prompt.
After adding a typedef long ssize_t, the code compiles fine, but linking fails with the following error:
source_file.obj : error LNK2001: unresolved external symbol _gnutls_free
C:\Path\to\executable.exe : fatal error LNK1120: 1 unresolved externals
I am calling gnutls_free to free some memory allocated and returned by the library. If I remove the call to gnutls_free, the project links successfully. Given that gnutls_free is just a global variable (containing a function pointer) exported by the library, I'm not sure why accessing it results in an unresolved reference to a different symbol. I have verified that gnutls_free is not #defineed to anything.
As a test, I tried doing gnutls_free_function test = gnutls_free; which also resulting in the link error. Running grep -w -r _gnutls_free . on the GnuTLS source code returns nothing, so I am at a loss.
Any ideas for getting this working would be greatly appreciated.
EDIT:
Adding __declspec(dllimport) to the declaration of gnutls_free in gnutls.h allows the link to succeed. Is there any way to accomplish this without maintaining a custom version of the header file?
There doesn't seem to be a way to have the linker or import library automatically dereference the IAT's pointer to the data item the same way that is done for functions (via a small trampoline function that is statically linked into the module importing the function). The __declspec(dllimport) attribute tells that compiler that this dereferencing needs to be done so it can insert code to perform the dereferencing of the IAT pointer implicitly. This allows exported data to be accessed and for functions allows the compiler to call the imported function via an indirect call through the IAT pointer rather than by calling the trampoline function.
See a couple of Raymond Chen's articles about dllimport for a good explanation of what goes on for function calls (he didn't discuss importing data, unfortunately):
Calling an imported function, the naive way
How a less naive compiler calls an imported function
The MS linker or import library doesn't have a mechanism to help the compiler get imported data in a 'naive' way - the compiler needs the the __delcspec(dllimport) hint that an extra dereference through the IAT is needed. Anyway, the point of all this is that it seems there's no way to import data except by using the __declspec(dllimport) attribute.
If you want to avoid modifying the gnutls distribution (which I can understand), here's one rather imperfect workaround:
You can create a small object file that contains nothing but a simple wrapper for gnutls_free(); since gnutls_free() has an interface with no real dependencies, you can have the necessary declarations 'hardcoded' instead of including gnutls.h:
typedef void (*gnutls_free_function) (void *);
__declspec(dllimport) extern gnutls_free_function gnutls_free;
void xgnutls_free(void* p)
{
gnutls_free(p);
}
Have your code call xgnutls_free() instead of gnutls_free().
Not a great solution - it requires your code to call a wrapper (so it's particularly not great if you'll be incorporating 3rd party code that might depend on gnutls_free()), but it might be good enough.
I'm using C++, and compiling & linking to OpenCV2 using "g++". One thing that bothers me is that all of the old cv-prefixed functions are still available and "pollute" my application.
Is it possible to make the OpenCV1 C cv-prefixed functions unavailable in the scope of my application and just keep the OpenCV2 cv:: namespaced ones?
Note: I haven't written C in a while, so please let me know if this is a silly question.
It depends on what do you really need. If you just want to make this code:
CvArr *arr;
cvAvg(arr);
cvAcc(arr, arr);
"not working" - you can just add this:
#define cvAvg nothing_interesting_cvAvg
#define cvAcc nothing_interesting_cvAcc
//you can change nothing_interesting_... to anything, but you can't use the same text more than once
//you include files
//...
//after your include files
#undef cvAvg
#undef cvAcc
before including any OpenCV file. If you now try to compile code you will see:
error C3861: 'cvAvg': identifier not found
If you change you code to use nothing_interesting_cvAvg(arr); instead of cvAvg(arr);, it will compile fine, but linker will fail, because:
: error LNK2019: unresolved external symbol _nothing_interesting_cvAvg referenced in function _main
Note that this will work only for this 2 functions, so you will have to find all functions which you want to "disable" and write similar code manually.
Functions which use "deactivated" functions will work fine, because they are already compiled, linked, etc - you will just call them from some files without changing anything in this files.