* template issue
@ 2004-09-14 18:20 Darko Miletic
2004-09-14 18:38 ` Eljay Love-Jensen
0 siblings, 1 reply; 3+ messages in thread
From: Darko Miletic @ 2004-09-14 18:20 UTC (permalink / raw)
To: gcc help
I have been playing with std::for_each and std::map and came with
interresting issue:
//main.cpp
#include <iostream>
#include <algorithm>
#include <string>
#include <map>
typedef std::map<int, std::string> mapType;
template <typename M>
inline void printMapValue(const M& value) {
std::cout << value.first << " - "
<< value.second << "\n";
}
template <typename T >
void print_map(const T& map_) {
std::for_each( map_.begin(),
map_.end(),
printMapValue<typename T::value_type>); // if
typename is removed here GCC reports error???
std::cout << std::endl;
}
int main(int argc, char* argv[])
{
mapType map_;
map_[0] = "111";
map_[1] = "222";
map_[2] = "333";
print_map<mapType>(map_);
return 0;
}
If I remove keyword typename from print_map function GCC reports this:
error: no matching function for call to `for_each(
std::_Rb_tree_iterator<std::pair<const int, std::string>, const
std::pair<const int, std::string>&, const std::pair<const int,
std::string>*>, std::_Rb_tree_iterator<std::pair<const int, std::string>,
const std::pair<const int, std::string>&, const std::pair<const int,
std::string>*>, <unknown type>)'
Why is typename needed here? Other compilers like BCB 5&6 and MSVC 7.1
compile this fine without typename keyword.
Darko
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: template issue
2004-09-14 18:20 template issue Darko Miletic
@ 2004-09-14 18:38 ` Eljay Love-Jensen
0 siblings, 0 replies; 3+ messages in thread
From: Eljay Love-Jensen @ 2004-09-14 18:38 UTC (permalink / raw)
To: Darko Miletic, gcc help
Hi Darko,
In this situation, GCC is compliant with ISO 14882 specification. BCB 5&6
and MSVC 7.1 are not.
The typename keyword is required because the compiler is NOT supposed to
presume that T::value_type is a type in that context, unless annotated with
typename.
HTH,
--Eljay
^ permalink raw reply [flat|nested] 3+ messages in thread
* RE: template issue
@ 2004-09-14 18:37 lrtaylor
0 siblings, 0 replies; 3+ messages in thread
From: lrtaylor @ 2004-09-14 18:37 UTC (permalink / raw)
To: darko, gcc-help
Other compilers may not require it, but it is in accordance with the
ANSI standard. I don't know where it talks about it in the standard,
but you can look in Stroustrup's "The C++ Programming Language" 3rd
edition, Appendix C, section 13.5. He gives a good explanation why this
is necessary. Perhaps someone else on the list can actually explain why
this is so, if you don't have access to a good C++ reference.
Thanks,
Lyle
-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On
Behalf Of Darko Miletic
Sent: Tuesday, September 14, 2004 12:20 PM
To: gcc help
Subject: template issue
I have been playing with std::for_each and std::map and came with
interresting issue:
//main.cpp
#include <iostream>
#include <algorithm>
#include <string>
#include <map>
typedef std::map<int, std::string> mapType;
template <typename M>
inline void printMapValue(const M& value) {
std::cout << value.first << " - "
<< value.second << "\n";
}
template <typename T >
void print_map(const T& map_) {
std::for_each( map_.begin(),
map_.end(),
printMapValue<typename T::value_type>); // if
typename is removed here GCC reports error???
std::cout << std::endl;
}
int main(int argc, char* argv[])
{
mapType map_;
map_[0] = "111";
map_[1] = "222";
map_[2] = "333";
print_map<mapType>(map_);
return 0;
}
If I remove keyword typename from print_map function GCC reports this:
error: no matching function for call to `for_each(
std::_Rb_tree_iterator<std::pair<const int, std::string>, const
std::pair<const int, std::string>&, const std::pair<const int,
std::string>*>, std::_Rb_tree_iterator<std::pair<const int,
std::string>,
const std::pair<const int, std::string>&, const std::pair<const int,
std::string>*>, <unknown type>)'
Why is typename needed here? Other compilers like BCB 5&6 and MSVC 7.1
compile this fine without typename keyword.
Darko
^ permalink raw reply [flat|nested] 3+ messages in thread
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2004-09-14 18:20 template issue Darko Miletic
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