我不明白为什么这个代码无法使用&T::b
和&T::c
时main()
编译由于“暧昧类模板实例”。它是g ++ 4.6.1的缺陷吗?歧义模板偏特供成员和成员函数
#include <iostream>
#include <string>
using namespace std;
struct T{
int a;
void b(){}
int c()
{
return 1;
}
};
template<typename CT, CT> struct member_helper;
template<typename FT, FT(T::*mem)>
struct member_helper<FT(T::*), mem> {
static string worker()
{
return "for members";
}
};
template<typename Return, typename... Args, Return(T::*fun)(Args...)>
struct member_helper<Return(T::*)(Args...), fun> {
static string worker()
{
return "for member functions returning non void";
}
};
template<typename... Args, void(T::*fun)(Args...)>
struct member_helper<void(T::*)(Args...), fun> {
static string worker()
{
return "for member functions returning void";
}
};
int main() {
cout << member_helper<decltype(&T::a), &T::a>::worker(); //prints for members, ok
cout << member_helper<decltype(&T::b), &T::b>::worker(); //cannot distinguish between all of the three
cout << member_helper<decltype(&T::c), &T::c>::worker(); //cannot distinguish between member function returning non void and member
}
编辑:
这里是完整的错误消息:
g++ -O0 -g3 -Wall -c -fmessage-length=0 -std=c++0x -MMD -MP -MF"main.d" -MT"main.d" -o "main.o" "../main.cpp"
../main.cpp: In function ‘int main()’:
../main.cpp:27:45: error: ambiguous class template instantiation for ‘struct member_helper’
../main.cpp:13:43: error: candidates are: struct member_helper
../main.cpp:17:78: error: struct member_helper
../main.cpp:21:59: error: struct member_helper
../main.cpp:27:8: error: incomplete type ‘member_helper’ used in nested name specifier
../main.cpp:28:45: error: ambiguous class template instantiation for ‘struct member_helper’
../main.cpp:13:43: error: candidates are: struct member_helper
../main.cpp:17:78: error: struct member_helper
../main.cpp:28:8: error: incomplete type ‘member_helper’ used in nested name specifier make: * [main.o] Errore 1
,这是copmiler版本:
使用内置的规格。 COLLECT_GCC =/usr/bin/g ++ - 4.6.real COLLECT_LTO_WRAPPER =/usr/lib/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper 目标:x86_64-linux-gnu配置:../src/configure -v --with-pkgversion ='Ubuntu/Linaro 4.6.1-9ubuntu3'--with-bugurl = file:///usr/share/doc/gcc-4.6/README.Bugs --enable-languages = c,C++,fortran,objc,obj-C++,go --prefix =/usr --program-suffix = -4.6 --enable-shared --enable-linker-build-id --with-system-zlib - -libexecdir =/usr/lib --without-included-gettext --enable-threads = posix --with-gxx-include-dir =/usr/include/C++/4.6 --libdir =/usr/lib --enable -nls --with-sysroot =/--enable-clocale = gnu --enable-libstdcxx-debug --enable -libstdcxx -time = yes --enable-plugin --enable-objc -gc --disable-werror - -with-arch-32 = i686 --with-tune = generic --enable-checking = release --build = x86_64-linux-gnu --host = x86_64-linux-gnu --target = x86_64-linux-gnu型号:posix gcc版本4.6.1(Ubuntu/Linaro 4.6.1-9u buntu3)
发布完整的错误消息。 – Nawaz 2012-03-27 16:19:08
(@Nawaz:T是一个真正的类型,上面的结构 - 虽然很混乱) – Mat 2012-03-27 16:22:59
@Mat:有趣。他正在使用模板,并已将“T”定义为类,从而造成混淆,即使英文字母有26个字母。 – Nawaz 2012-03-27 16:24:16