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You don't have to put the definitions in the header, just the declarations.
In header file:
template <class T> class CMyTemplate
{
public:
virtual void Method1(void*);
};
In cpp file:
template <class T>
void CMyTemplate<T>::Method1(void*){}
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Hello again 
thanks for ur reply... yes, so say in this program, here is the problem i am facning...
Now in the main function, if I try to create an object . .like
CMyTemplate<int> objT;
it gives me linking error
error LNK2001: unresolved external symbol "public: virtual void __thiscall CMyTemplate<int>::Method1(void *)" (?Method1@?$CMyTemplate@H@@UAEXPAX@Z)
waiting for your reply..
thanks
hrishi
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Where is the code for Method1()? I find it rather difficult to understand why you are using templates when you seem not to have mastered the basics of classes yet.
The best things in life are not things.
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Code In xxx.h file ::>>
--------------------------------------
template <class T>
class CMyTemplate
{
public:
virtual void Method1(T TDummy);
};
Code in xxx.cpp file ::>>
--------------------------------------
#include "xxx.h"
template <class T>
void CMyTemplate<T>::Method1(T TDummy)
{
TDummy = TDummy + 1;
}
Code in main function ::>>
--------------------------------------
CMyTemplate<int> objT;
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I cannot see anything wrong with this, and I have copied it into a test program of my own and it compiles and links successfully. There must be something different in your implementation that you have not shown in your message.
Also, please surround your code snippets with <pre> tags (use the code block button) so it shows more clearly, like this:
template <class T>
void CMyTemplate<T>::Method1(T TDummy)
{
TDummy = TDummy + 1;
}
The best things in life are not things.
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thanks for your reply and your suggestions,
Oh, I am really unable to figure it out. And there is no difference as such in my implementation.
FYI, the linking error which i am getting is..
TestProject.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall CMyTemplate<int>::Method1(int)" (?Method1@?$CMyTemplate@H@@UAEXH@Z)
modified on Thursday, July 7, 2011 10:35 PM
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I have no idea what you are doing wrong, as you have not shown your code. Here is an implementation that works; just copy this code and paste into a single .cpp file and build it.
#include <iostream>
using namespace std;
template <class T>
class CMyTemplate
{
public:
virtual void Method1(T& TDummy);
};
template <class T>
void CMyTemplate<T>::Method1(T& TDummy)
{
TDummy = TDummy + 1;
}
int wmain()
{
int zz = 25;
CMyTemplate<int> objT;
objT.Method1(zz);
wcout << L"Value of the dummy: " << zz << endl;
return 0;
}
The best things in life are not things.
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I think there is a misunderstanding. Sorry if my words were not able to explain my doubt.
If you please refer to my main-doubt
Could anyone please tell me, is there any way to separate the definition of the methods of a template class ,from header file to .cpp file.
The code which you have provided works absolutely fine, in just one file.
Just that I wanted to know, if there is any way to separate the definitions of the method in an another .cpp file. (Just like a normal class where we declare in .h and implement in .cpp)
template <class T>
void CMyTemplate<T>::Method1(T& TDummy)
{
TDummy = TDummy + 1;
}
and the declaration in an separet .h file
template <class T>
class CMyTemplate
{
public:
virtual void Method1(T& TDummy);
};
thanks in advance
hrishi
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OK, I think I understand what you are asking.
You can put the definition and the implementation into a single .cpp file, but it must all be in the same file - as was the case with my sample. You cannot put the definition into one .cpp file and the implementation into another, as the information required by the compiler must be available in one compilation unit. It is much simpler to follow the default and put your definitions into a .h file and your implementation into the .cpp file(s). Doing it this way means that you can split the implementation across multiple files, as long as each one includes the definitions.
The best things in life are not things.
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If you are still looking for an answer, I posted an article explaining this just today.
http://www.codeproject.com/Articles/236927/All-your-base64-are-different-to-us
In short, there is a way, provided you know all template types you will be using. I'll copy the example I had in the article here:
-------------------------------------
-- In my_template.h file
...
template <typename T>
T my_temp_func(const T& t);
-------------------------------------
-- In my_template.cpp file
#include "my_template.h"
template <typename T>
T my_temp_func(const T& t)
{
return t;
}
int my_temp_func<int>(const int& t);
-------------------------------------
-- In using_my_template.cpp
#include "my_template.h"
...
int i = my_temp_func<int>(4); string s = my_temp_func<string>("Abob");
In the example above, the declaration in the last line of my_template.cpp tells the compiler there’ll be a variant of the template function that uses int as template parameter. Okay, says the compiler, I’ll put an inline copy there. Since the generic definition is right there in the same compilation unit (ie my_template.cpp), this is something the compiler can do – it has all the information it needs.
The result of that is that in the compiled file (probably called my_template.obj) there is now a function that has the signature int my_temp_func(const int& t). This is a fully defined specialisation of a template function, so to the linker it looks just like a normal function.
However, the linker won’t be able to find a string specialisation, so this will generate a linker error.
In
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Templates behave a lot like inline functions. The entire implementation is required to be declared in the include file for the compiler to use it correctly.
I believe you have described this method in your question, but I would like to start here, because it is the method I prefer if I dont want a single .h file implementation. I will use the file name Tmp.x for all of the examples, where x is the extension.
1) You declare all of your template classes and functions in your file Tmp.h .
2) Then implement all of the functions in a separate file with an extension such as Tmp.inl (inline). It is important that when the function definitions appear outside of the class definition, that you declare each function declaration with inline. Otherwise if you include this header file in multiple places, you will get linker errors for duplicate symbols.
3) At the bottom of Tmp.h and the line #include "Tmp.inl". The file implemented in step 2.
If you prefer to have the file extension to still be .cpp, you can use that as well. You would follow all of the steps the same way, and include the .cpp file at the end of the .h file. The only difference, in your Visual Studio project, you will have to change the settings for the file so that it does not get compiled like the other .cpp files. It is already included in a header file.
You cannot get around having the Template implementation available to the compiler when it sees the first usage of the template.
Why? Because that is the point where the compiler generates the actual code from the template.
Originally there was supposed to be a keyword "export" to allow the templates to be defined like regular classes, but that never became part of the standard, and therefore is not available.
Hopefully this helps.
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thanks a lot,
it was really helpful 
hrishi
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Your basic problem appears to be to understand how Header Files, cpp Files, the Compiler and the Linker work.
First the Compiler. The Compiler builds an Object File. This is a Binary representation of a cpp File. It containd the CPP Code you wrote, converted to machine code as well as a whole raft of information needed later. The Compiler contains a thing, called a Pre-Processor. It prepares your CPP file before actual compilation. Conceptually it produces a New Source File. It copies your file Line by Line. but if it finds a statement like #include "MyBeautifulHdr.h", it does not copy the include statement, but, instead writes the entire contents of "MyBeautifulHdr.h" at the location of the '#include' statement. When it encounters a #define FOO 1 statement, it undertakes to replace henceforth every future occurrence of 'FOO' with 1. It goes on like that at infinitum, and the final file offered to the compiler has all '#includes, #defines, #if's etc resolved.
At that stage the compiler does not know ( and does not care) from what file what item came from, (except for error reporting). It just builds the Object File, (if it Can)
if it cannot, you get an error.
Each of the Object Files generated roughly correspond to the code you wrote in a cpp file.
An extern declaration is a promise to the compiler that somewhere in an other file or library, an item of that specification exists.
The Linker tries to build an executable out of all those object files. In doing so, it may also include Object files written by others, e.g. those written by Microsoft, which came with your compiler package. To make that process more efficient, multiple obj files can be gathered together into a library (.lib) file
If the linker cannot find a named item, or, finds more than one, the linker will fail building the executable.
Getting a Full understanding of how your tools work will answer your queery.
regards,
Bram van Kampen
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I have this benchmark program that started off as a console program and I am now well into making work with a window instead. It's all Win32 for the most part with a smattering of C++ STL for some containers.
I launch the background via a keyboard command ctrl-r
case (0x52):
if(GetKeyState(VK_LCONTROL) || GetKeyState(VK_RCONTROL)) {
_beginthread(showtime, NULL, NULL);
}
break;
So what am I doing wrong, the background thread runs for while but crashes, used to work fine.
http://www.contract-developer.tk
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What is it the background thread doing? Do you get an exception or any other information when it crashes?
The best things in life are not things.
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void showtime(void *dummy) {
computing = true;
output.clear();
output = _TEXT("Fibonacci 3.0.0 for Windows");
output += ToString("/n/l/n/l");
output += _TEXT("(c) 2010-1 583727 BC Ltd, All Rights Reserved.");
output += _TEXT("/n/l");
output += _TEXT("Free for peronsal use only");
output += _TEXT("/n/l/n/l");
output += _TEXT("Commercial and government use requires a license");
output += _TEXT("/n/l/n/l");
output += _TEXT("To acheieve consistant results, run this program in the clean boot mode");
output += _TEXT("/n/l");
output += _TEXT("Click on start, in the seach box enter 'msconfig' and choose the startup tab, disable everyting and reboot");
output += _TEXT("/n/l/n/l");
output += _TEXT("RAM Performance ");
output += ToString(benchmark(fib2));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Scalar Performance ");
output += ToString(benchmark(fib3));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("CPU Large Multiplication Performance ");
output += ToString(benchmark(fib4));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
v.resize(0); t.resize(0);
output += _TEXT("Recursive Factorial Performance ");
output += ToString(benchmark(RunFact));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Bubble Sort Performance ");
output += ToString(benchmark(RunBubbleSort));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Insertion Sort Performance ");
output += ToString(benchmark(RunInsertionSort));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Shell Sort Performance ");
output += ToString(benchmark(RunShellSort));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Quick Sort Performance ");
output += ToString(benchmark(RunQuickSort));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Merge Sort Performance ");
output += ToString(benchmark(RunMergeSort));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Heap Sort Performance ");
output += ToString(benchmark(RunHeapSort));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel Bitwise Sieve of Eratosthenes Performance ");
output += ToString(benchmark(sieve));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel Goldbach Conjecture Performance Performance ");
output += ToString(benchmark(goldbach));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel Collatz Conjecture Performance ");
output += ToString(benchmark(RunCollatz));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel vector<float> normalization ");
output += ToString(benchmark(vtestfloat));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel vector<double> normalization ");
output += ToString(benchmark(vtestdouble));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel vector<std::complex> normalization ");
output += ToString(benchmark(vtestcomplex));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel matrix<float> multiplication ");
output += ToString(benchmark(mtest1));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel matrix<double> multiplication ");
output += ToString(benchmark(mtest2));
output += _TEXT(" seconds");
output += _TEXT("/n/l");
output += _TEXT("Parallel matrix<std::complex> multiplication ");
output += ToString(benchmark(mtest3));
output += _TEXT(" seconds");
output += _TEXT("/n/l/n/l");
computing = false;
MessageBox(NULL, L"Completed", L"Fibonacci", MB_OK);
}
http://www.contract-developer.tk
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What is output and why are you putting so much text into it for no apparent reason?
The best things in life are not things.
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typedef std::basic_string<wchar_t> tstring;
tstring output;
The output will eventually be placed on the clipboard as a text
http://www.contract-developer.tk
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You have still given no information as to where this crashes, and what exceptions or other diagnostic information you see. We cannot guess what happens on your system; have you tried running it through the debugger?
The best things in life are not things.
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I am going to use MessageBox all over the module and see how far it gets.
One question, do I need to use the exitthread anywhere?
http://www.contract-developer.tk
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VeganFanatic wrote: do I need to use the exitthread anywhere?
Impossible to say; it depends what your program is actually trying to do. Are you sure you need multiple threads?
The best things in life are not things.
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Putting that module into a thread was to make the program able to quit at any time.
This was to make sure the message handler is able to get messages.
http://www.contract-developer.tk
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From looking at the code you posted, its probably because another thread accesses or destroys output while the thread is still using it. The way you're using the string is also very bad practice since you're forcing it to reallocate memory constantly for the string and this is very inefficient. Why not get all the information you need once, then allocate/format your string? This would allow the thread to run way faster and more efficiently.
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When you have this run on one thread, does it complete properly?
I would do 3 things to trouble shoot and improve the code:
1) Add another command to your console entry, that allows you to start the "showtime" function, and run it one the same thread. Verify that it functions properly.
2) Enable Exceptions. I assume you are using Visual Studio of some sort, if not you will have to figure out how to do this for your debugger. In Visual Studio you can do this at the Debug | Exceptions Menu. Enable: C++ Exceptions, Native Run-Time Checks and Win32 Exceptions.
When you run your application in the debugger and it crashes, you will be right at the point in code the exception is thrown. Then you can look at the stack and all of the other helpful information.
3) Break up all of the work done in "showtime" into a smaller pieces. Probably a common function that prints out the basic text and runs the test you initiate. Then in "showtime" you would make multiple calls to your smaller function. This will help make your code more manageable.
From looking at your code, my guess is that one of the test routines is returning a NULL or some value that the string functions dont like, or is failing internally.
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Hello all,
Could anyone please give me a efficient method and suggestions for the following.
I have many classes already in my VC++ project, which were build on MFC. Meaning the data types were MFC based. like CByteArray, CString etc etc. Now I need to avoid the uses of MFC data types , and introduce STL data types.
could you please give me an efficient and less time consuming method to migrate the same. For eg: shal I use my own classes to mimic MFC classes like CString. or correct each uses/mehtod of MFC classes wherver there is, and change with STL based methods.... I am a bit confuse. please suggest me
thanks in advance
Hrishi
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