Problem compiling C++ template code

Question

I have the following template:

template<class Matrix> 
Matrix horizontal_join (const Matrix& m1, const Matrix& m2) {

ASSERT (rows (m1) == rows (m2), "unequal number of rows");
typedef typename Matrix::value_type Scalar;
Matrix r (rows (m1), nbcol (m1) + nbcol (m2));
  for (unsigned i=0; i<nbrow(m1); i++) {
      for (unsigned j=0; j<nbcol(m1); j++)
     r(i,j)= m1(i,j);
      for (unsigned j=0; j<nbcol(m2); j++)
     r(i,j+nbcol(m1))= m2(i,j);
  }
  return r;
}

defined in some library called "MATRDSE.m". There is also defined a structure called "matrsdse" in a file "matrdse.hpp" which represents a dense matrix type and which has several

-constructors,e.g matrdse(int nrRows, int nrCols, const value_type *src, ByRow() )

-and methods, e.g. transpose().

I want to use the "horizontal_join" template in my main function:

#include <matrdse.hpp>
#include <MATRDSE.m>

typedef matrdse<double> MxPoly;    

int main{

    double v[]={1,2,1,1,3,4,2,2,5,5,5,5,-2, 1,2,3,1, -2.8,-2.4,1,.2,5.8};
matrdse<double> A(4,4,v,ByRow());
std::cout<<"A="<<endl<<A<<endl;
matrdse<double> AT(A);
AT.transpose(); std::cout<<"Transpose(A)="<<endl<<AT<<endl;
MxPoly B;
B=horizontal_join<MxPoly>(A,AT);
cout<<B<<endl;

    return 0;

 }

Everything works fine, until "horizontal_join" is called and returned in B. I get the following compilation error:

 main.cpp:168: error: 'horizontal_join' was not declared in this scope
 main.cpp:168: error: expected primary-expression before '>' token

I do not understand the error. As I see it I do not know how to call the template..

Thank you in advance for any suggestions, madalina

yes, I have, I have forgotten to include it in the question here.sorry — madalina
– madalina, Commented Jul 23, 2009 at 8:54
Please make the title of the question more descriptive. "use of templates" gives barely any idea of what it's about. Suggestion: "Confusing error when calling C++ template function" — flodin
– flodin, Commented Jul 23, 2009 at 8:56
May it be that the template in the header is declared inside a namespace? — sharptooth
– sharptooth, Commented Jul 23, 2009 at 8:56
posting the actual code using copy & paste rather than typing in an approximation would be a good idea — anon
– anon, Commented Jul 23, 2009 at 9:48

Ari · Accepted Answer · 2009-07-23 09:04:49Z

1

Is this the actual code? You have the #define (a bad idea in itself) reversed. It should be

#define MxPoly matrsde<double>

answered Jul 23, 2009 at 9:04

Ari

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3 Comments

madalina Over a year ago

I used typedef matrdse< polynomial_t> MxPoly; sorry for mistyping.

Ari Over a year ago

is polynomial_t the same as double? If not, there's your problem.

madalina Over a year ago

yes indeed this was the error. I need typedef matrdse<double> MxDouble; for the template used with this double matrix not a matrix of polynomials indeed.

1800 INFORMATION · Accepted Answer · 2009-07-23 09:01:44Z

0

I guess the problem is the combination of your preprocessor macro here (is this even right, do you have the name of the macro before the type?):

#define matrdse<double> MxPoly;

and the template instantiation here:

B=horizontal_join<MxPoly>(A,AT);

Note that the instantiation line expands in the preprocessor to this:

B=horizontal_join<matrdse<double>>(A,AT);

The template-template thing ending in >> is a well known compiler error that is masked here by the macro. I guess if you change the template instantiation line to this it goes away:

B=horizontal_join<MxPoly >(A,AT);

I suggest you need to use some more consistent naming, and favour typedef over macro as it will not have this problem:

typedef matrdse<double> MxPoly;

answered Jul 23, 2009 at 9:01

1800 INFORMATION

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2 Comments

Carl Seleborg Over a year ago

Talk about having the same answer! :-)

Pete Kirkham Over a year ago

The macro #define matrdse<double> MxPoly; tells the preprocessor to replace the token matrdse with the tokens <double> MxPoly;

peterchen · Accepted Answer · 2009-07-24 20:27:24Z

0

#define matrdse<double> MxPoly;

one semicolon to much

edited Jul 24, 2009 at 20:27

answered Jul 23, 2009 at 9:02

peterchen

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