template member function

[PengYu.UT]

I can't figure out what is wrong with following program. Would you
please help me? The error line is marked with error.

Peng

#include <iostream>

template <typename T>
class B{
public:
T t;
};

class A{
public:
template <typename T>
void doit(typename B<T> &b){//error
std::cout << "in " << std::endl;
}
};

int main(int argc, char *argv[])
{
B<int> b;
A a;
a.doit<int>(b);
}

 

[Jacques Labuschagne]

void doit(typename B<T> &b){//error
std::cout << "in " << std::endl;
}

Take out the "typename" keyword.

Jacques.

 

[Victor Bazarov]

I can't figure out what is wrong with following program. Would you
please help me? The error line is marked with error.

Peng

#include <iostream>

template <typename T>
class B{
public:
T t;
};

class A{
public:
template <typename T>
void doit(typename B<T> &b){//error

"error". Which error? Does your compiler just say "error" or
does it actually try to explain what it thinks is wrong?

Anyway, my compiler compiles it without a problem. It, of course
doesn't mean the code is fine. You need to remove the second
'typename' in this declaration. The line should be

std::cout << "in " << std::endl;
}
};

int main(int argc, char *argv[])
{
B<int> b;
A a;
a.doit<int>(b);
}

V

 

[Jacques Labuschagne]

"error". Which error? Does your compiler just say "error" or
does it actually try to explain what it thinks is wrong?

My compiler could certainly have been more helpful, IMHO. GCC 3.3 says
foo.cc:12: error: parse error before `&' token
It was good enough for me, but I can understand PengYu's confusion.

Jacques.

 

[Greg]

My compiler could certainly have been more helpful, IMHO. GCC 3.3 says
foo.cc:12: error: parse error before `&' token
It was good enough for me, but I can understand PengYu's confusion.

But imagine the compiler's confusion to run into the "typename" keyword
in what it thought was going to be a method declaration. At that point
the compiler has no idea what the programmer is trying to write, so it
has no idea which part of the expression the programmer should remove.

Greg

 

[Greg Comeau]

But imagine the compiler's confusion to run into the "typename" keyword
in what it thought was going to be a method declaration. At that point
the compiler has no idea what the programmer is trying to write, so it
has no idea which part of the expression the programmer should remove.

You told it typename. It is believe you:

"ComeauTest.c", line 17: error: a class or namespace qualified name is required
void doit(typename B<T> &b){//error

(as per the rules of typename) or it doesn't.