I am using Visual C++ 2008 Express for the first time for a project. And I can't seem to be able to split the .h & .cpp files for classes I'm writing. I was under the impression that you add a header file and prototype the class in there, and then you add a .cpp file with the implementation into your source files directory. Then when you include the .h it would automatically include the .cpp implementation files. Is this correct or am I missing something?
Not sure if this is the same as in Express version. But you can also add a new C++ class with header (.h) and source (.cpp) at the same time by right clicking on the project -> Add -> Class...
By including the .h file using #include, doesn't mean the actual implementation (in another .cpp file) is also include in your source file. The content of .h file which are class and method prototypes is only included. These prototypes allow you to make use of the classes declared in header file (without including real C++ code.)
Each source files (.cpp) are first compiled into object files. All these object file are then linked together to create single executable file. The referenced symbols in, each object file, are actually linked to their implementation during this linking process (http://www.cprogramming.com/compilingandlinking.html)
I don't remember the rules, but sometimes the IDE assumes you're putting all your code in the header file. This is legal, but not a common preference.
Related
My solution contains several c# projects.
It's easy to add "refernce" from one project to another(References-Add Reference-Project). After that I can use classes from referenced project.
How can I do the same for native c++ projects? What kind of projects should I create? Console application/DLL/Static library?
There are two things in C / C++ :
Headers file, that will tell your program what they can use (e.g. class, function prototype declaration)
Implementation, either as a
source code that you recompile with your program
static lib (.lib on windows)
dynamic lib (.dll on windows)
You need both to compile your program with parts from another project.
If you only need a class from a big library and you have the source of this library it may be easier to reference the file corresponding to this class (and its dependencies of course). But if you need more, you should add the other project's directory to the include path of your current project in VCC, and link against the library (either static or dynamic, according to your needs).
I'm trying to create a shared library for Linux such that:
other programs can use its functions and its objects
the code is not visible to final user
What i did is create a shared library with Eclipse. This library uses pthreads.
I generated .so and .lib. The .lib is in LIBRARY/Lib while the .so is in LIBRARY/Release.
Then i created another project which should use this library and i gave the path of the .lib file and the path of the .h file which only contains the inclusions of all the necessary .h of the library.
All seems working but when i run the program it crashes. When debugging it I receive the following message:
Can't find a source file at "pthread_mutex_lock.c"
Locate the file or edit the source lookup path to include its location.
What's wrong? Can someone help me please?
EDIT: I changed nothing and now I have a different error, some lines before the previous:
Can't find a source file at "random.c"
Locate the file or edit the source lookup path to include its location.
other programs can use its functions and its objects
the code is not visible to final user
These two goals directly contradict each other, and achieving both at the same time is impossible on Linux.
If some program can use your library, then I can write a new program that can do so as well.
I have two existing executables A and T, in the same solution that both ran just fine before I touched them. In executable A is a header defining a class P, and a prototype for a static instance MyP. The definitions are compiled in project A. In executable T, I wanted to call member functions of MyP in project A, so I added dllimport/export macros to the declarations of the class and MyP in the headers (not at the definitions), and included the headers in project T. The dllimport/export macros are standard, and A_EXPORTS is defined in project A, but not in T.
#ifdef A_EXPORTS
#define A_API __declspec(dllexport)
#else
#define A_API __declspec(dllimport)
#endif
//various definitions and includes, defining ENUM_RECORDING_TYPE and ERROR
A_API HFILE viosopen(const _TCHAR *path, ENUM_RECORDING_TYPE rt, int flags);
A_API struct P {
ERROR B(SHORT phraseNum);
};
A_API extern P MyP;
I added project A as a dependency on project T in the solution. A still compiles fine, but T comes up with unresolved external symbol "__declspec(import) <snip> referenced in function <snip> for the function calls, and unresolved external symbol "__declspec(dllimport) class P MyP" <snip> for the static object. I also see in the output log, right after it starts linking: Creating library Debug/A.lib and object Debug/A.exp which seems ominous since it's supposed to be linking against the existing executable.
My question is: how can I tell MSVC 2010 where those are? I thought simply setting A as a dependency would have it figure that out automatically. I can link against the existing executable, right?
To statically link your program you don't need the __declspec() stuff and you don't need a separate project to create a LIB file. I think you can just link using the .obj file from your A project.
Your A project has a header file and presumably has a .cpp file that contains the implementation of the items described in that header. Let's say your header file is foo.h and the associated implementation is foo.cpp. When compiled, there should be a foo.obj intermediate file in the <solutiondir>\A\Debug or <solutiondir>\A\release intermediate folder. That file can be used by the linker.
In project T's properties, find Linker | Input and change the "Additional Dependencies" property to include the foo.obj file. One approach would be to use a relative file path to locate the file - for example ..\A\Debug\foo.obj in your debug configuration. Another approach is to use the simple file name in "Additional Dependencies" - foo.obj - and then use Linker | General | Additional Library Directories" to help the linker find the file - e.g., ..\A\$(IntDir). Using the $(IntDir) macro has the advantage that the same value works for Debug and Release settings.
Remember to set up a build dependency from your T project to your A project to be sure the A project is compiled first. Otherwise the foo.obj file might not exist when the T linker comes to look for it. In the Solution properties, select Project Dependencies and then set Project T depends on Project A.
To dynamically link you need to use the A.LIB file as #ajay said. The __declspec(DllImport) tells the compiler what functions and data you are importing but doesn't tell it where you are importing those things from.
Using the A.LIB file as input to the linker is much the same as using the foo.obj file in the statically linking case except that the lib file ends up in the solution output directory <solutiondir>\Debug instead of the project intermediate directory <solutiondir>\A\Debug.
This walkthrough on creating and using a DLL might be useful background.
I asssume project A is DLL not an EXE, which is successfully producing a LIB file.
You need to use the A.LIB as Linker Input in project B. Just producing LIB file wont make other projects automatically link to it.
I am banging my head against a wall here.
All i want is to link a static .lib file in a cpp windows forms application! So, i have an include folder in my project folder that holds header files for that .lib (lib is Yaml-cpp if someone wonders). And i have a lib folder that has the .lib files for that library.
I tested it on a blank project
1.I make a new windows forms project in VS2008, in C++.
2.I go to project properties - c/c++ general and additional include directories that have yaml-cpp header files
3.I go to linker and add path to my lib directory
4.I go to linker - input and add my .lib file
5.I check linker command line and it contains my .lib file so it must be all set.
6.Then i write the sample code in an onbutton function body (which appears in form1.h fie).
Sample code is from here http://code.google.com/p/yaml-cpp/wiki/HowToParseADocument and its just as simple as:
#include <fstream>
#include "yaml.h"
and then:
std::ifstream fin("test.yaml");
YAML::Parser parser(fin);
YAML::Node doc;
while(parser.GetNextDocument(doc)) {
//do nothing yet
}
7.And then i compile and have 10 "unresolved externals".
I have looked into another project that uses same library, and it has exactly same directory structure, same name of .lib added in linker - input - additional dependencies, same .lib and .h files. And it works for that project- but it doesnt work for me.
What in the world is wrong?
EDIT: I tried making new windows 32 console application and it worked correctly. I then tried to make another fresh windows forms application and it failed.
It is confirmed now. Same steps for linking a library work in console application and fail in windows forms application. WHY?
What you've done seems correct from your explanation, let's do some blind troubleshooting.
Try giving full path instead of relative path for library path and additional include directories. (but as u said that the file is getting read, that should be the problem.)
If you are using a copy of original libyaml-cppmdd.lib and its include file, check whether the header file that gets included is of the same version as the lib.
Check whether there are any functions in any part of the code that is having a declaration but no definition.
Check whether you're accessing any private functions from the library.
Please read this Microsoft article on Troubleshooting UnResolved External Symbol error.
Hope it helps!
I have a myheader.h file, i have included it successfully in my VC++ project, but i am not able to use any of it functions. It gives the error Unresolved external symbol (my function definition). What am i missing?
//Here is my code snippet
#include "myHeaders/myheader.h"
void main (){
head_gen();
}
It doesnt build and the error is
Unresolved external symbol void__head_gen()
etc. Has it something to do with .lib file or something else?
You need the implementation of the function head_gen(). This can be in
a source file,
an object file or
a library
You should have one of them gotten with the header file.
If you have a .cpp file, add it to your project.
If you have a .obj or .lib file, add it as dependecy in the Project Properties:
Configuration Properties / Linker / Input -> Additional Dependencies
If the .obj or .lib file is in a different directory than your project, don't forget to add the path:
Configuration Properties / Linker / General -> Additional Library Directories
I develop mostly on Linux and use vi as an editor. But when I see such errors, it usually is one of the following reasons:
The function head_gen() is defined under a namespace and the source code where head_gen() is used does not have the using namespace statement.
Has head_gen() been defined in myHeader.cpp? That could be another reason why the function is not "visible".
HTH,
Sriram