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How can I fix it?

shafiul0304034 (33)
I created a header file (MemoryTest.h) and a .cpp file (MemoryTest.cpp) with template parameter but I got the linker error once i linked the header file in the main file. I have tried to allocate the memory dynamically for any data type

In single file, it is working. But once I have spitted the code into a header file (MemoryTest.h), source file (MemoryTest.cpp) and a main file (Main.cpp), the linker error is pop up. Error :: LNK2019 unresolved external symbol "void __cdecl allocateData1DbyMalloc<float,int>(float * *,int)".


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  // MemoryTest.h
    #ifndef MEMORYTEST_H   
    #define MEMORYTEST_H

    template <class type1, class type2>
    void allocateData1DbyMalloc(type1**, type2);

    template <class type1>
    void deAllocateData1DbyFree(type1**);

    template <class type1, class type2>
    void allocateData2DbyMalloc(type1***, type2, type2);

    template <class type1, class type2>
    void destroyMatrix2DbyFree(type1***, type2);
    #endif


    //MemoryTest.cpp file contains the definition of the function which were declared in MemoryTest.h file.
 
    #include "MemoryTest.h"
    #include<cstdlib>
    #include <typeinfo>
    #include <cstring>
    #include<iostream>

    template <class type1, class type2>
    void allocateData1DbyMalloc(type1** data1D, type2 nRow)
    {
	//	cout << typeid(type1).name() << "    " << typeid(**data1D).name() << "    
    " << typeid(*data1D).name() << "    " << typeid(data1D).name() << endl;
	*data1D = (type1*)malloc(nRow * sizeof(type1));
	if (data1D == NULL) {
		printf("ERROR: out of memory\n");
	}
    }

    template <class type1>
    void deAllocateData1DbyFree(type1** data1D)
    {
	//	std::cout << typeid(type1).name() << "  " << typeid(data1D).name() << 
    "  " << typeid(*data1D).name() << std::endl;
	free(*data1D);
    }

    template <class type1, class type2>
    void allocateData2DbyMalloc(type1*** data2D, type2 nRow, type2 nColumn)
    {
	*data2D = (type1 * *)malloc(sizeof(type1*) * nRow);
	if (data2D == NULL) {
		printf("ERROR: out of memory\n");
	}
	for (int i = 0; i < nRow; i++) {
		(*data2D)[i] = (type1*)malloc(sizeof(type1) * nColumn);
		if ((*data2D)[i] == NULL) {
			printf("ERROR: out of memory\n");
		}
	}
    }
    template <class type1, class type2>
    void destroyMatrix2DbyFree(type1*** data2D, type2 numberOfRow) {
	//	std::cout << typeid(type1).name() << "    " << typeid(**data2D).name() 
    << "    " << typeid(*data2D).name() << "    " << typeid(data2D).name() << 
    std::endl;
	for (int row = 0; row < numberOfRow - 1; row++)
		free((*data2D)[row]);
	free(*data2D);
    }



    //Main.cpp contain the vector and Matrix array which are declared inside of a main function. For the allocation of the memory it called to MemoryTest.h.

    #include "MemoryTest.h"
    int main() {
	int n = 4;
	float* constrainVector;
	allocateData1DbyMalloc(&constrainVector, n);
	constrainVector[0] = 6.0;
	constrainVector[1] = 25.6;
	constrainVector[2] = -11.2;
	constrainVector[3] = 12.7;
	deAllocateData1DbyFree(&constrainVector);

	float** matrix2D;
	allocateData2DbyMalloc(&matrix2D, n, n);
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			matrix2D[i][j] = (double)(i+j);

	destroyMatrix2DbyFree(&matrix2D, n);

	return 0;
    }
Ganado (6785)
You can't separate template definitions from their declarations. Compiler needs to know the full definition of a template when creating a class/function out of it.
Handy Andy (5051)
Hello shafiul0304034,

For what it is worth this is something I tried that worked.

I started by changing "main" like this:
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#include<cstdlib>
#include <typeinfo>
#include <cstring>
#include<iostream>

#include "MemoryTest.h"

int main()
{
	constexpr int N = 4;


I changed the header file to:
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#ifndef MEMORYTEST_H   
#define MEMORYTEST_H

template <class type1, class type2>
void allocateData1DbyMalloc(type1**, type2);

template <class type1>
void deAllocateData1DbyFree(type1**);

template <class type1, class type2>
void allocateData2DbyMalloc(type1***, type2, type2);

template <class type1, class type2>
void destroyMatrix2DbyFree(type1***, type2);

#include "MemoryTest.idl"

#endif

Note the line in bold.

Then I saved the ".cpp" file with the ".idl" extension. Also this was a file that is not part of the solution/project, but an individual file.

This goes along with what Ganado is saying about not separating the files. Although you can work with separate files they will compile as one file.

Hope that helps,

Andy
shafiul0304034 (33)
Hi Handy and Ganado, Thanks for the answer. I respect your time and effort. As a beginner, I am still learning. My complete C++ code might run in Window enviroment but also in Linux environment in future. In such a case, I am afraid to use the .idl file. As far as I know, it's for the windows application. I learn today that there should not be any separate definition and declaration for the template file. In such a case, how it would be if I eliminate the header file (MemoryTest.h) and directly add the file MemoryTest.cpp into Main.cpp file?.
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