function templates

[josh]

Hi if I want only write a template function in a non-template class I
have an error:

in Array.h
class Array
{
public:
Array() {}
~Array() {}

template <typename T> friend
void printArray(T el[], int dim);

};

in Array.cpp

template <typename T>
void Array:rintArray(T el[], int dim)
{
cout << "[ ";
for(int n=0; n < dim; n++)
{
cout << el[n] << " ";
}
cout << "]\n";
}

then in cpp_test.cpp

Array *a = new Array();

double d[] = {11.1,11.2};
int i[] = {12,13};
char c[] = {'a','b'};

a->printArray(d, 2);
a->printArray(i, 2);
a->printArray(c, 2);

but here the compiler issues this error:
.../cpp_test.cpp:21: undefined reference to `void
Array:rintArray<double>(double*, int)'
.../cpp_test.cpp:22: undefined reference to `void
Array:rintArray<int>(int*, int)'
.../cpp_test.cpp:23: undefined reference to `void
Array:rintArray<char>(char*, int)'

why?

 

[Ian Collins]

Hi if I want only write a template function in a non-template class I
have an error:

in Array.h
class Array
{
public:
Array() {}
~Array() {}

template <typename T> friend

^^^^^^
A friend function isn't a member function. Either drop the friend, or
drop the class prefix in the definition.

 

[josh]

^^^^^^
A friend function isn't a member function. Either drop the friend, or
drop the class prefix in the definition.

sorry the code above is wrong. Take it without friend! so:

class Array
{
public:
Array() {}
~Array() {}

template <typename T>
void printArray(T el[], int dim);

};

and

template <typename T>
void Array:rintArray(T el[], int dim)
{
cout << "[ ";
for(int n=0; n < dim; n++)
{
cout << el[n] << " ";
}
cout << "]\n";
}

and my question is: can we write only a funcion template in a non-
template class like Java do?

I'm a Java programmer that wants to pass to C++ and I want to convert
my Java background into C++...
and this is very HARD!

 

[Ian Collins]

*Please* don't quote signatures.

sorry the code above is wrong. Take it without friend! so:

In that case, your compiler probably doesn't support compiling templates
in separate compilation units. Put the template definition in the header.

 

[josh]

*Please* don't quote signatures.


In that case, your compiler probably doesn't support compiling templates
in separate compilation units. Put the template definition in the header.

great it runs! If I want compiling templates in separate compilation
units how do make that? I'm using
gcc 4.1.1 on Linux

 

[Ian Collins]

great it runs! If I want compiling templates in separate compilation
units how do make that? I'm using
gcc 4.1.1 on Linux

By not quoting signatures?

You can't, gcc doesn't support the export keyword.