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考慮下面的程序:爲什麼我不能在C++中使用模板化的typedefs?
#include <iostream>
#include <algorithm>
using namespace std;
template<class T>
struct A {
typedef pair<T, T> PairType;
};
template<class T>
struct B {
void f(A<T>::PairType p) {
cout << "f(" << p.first << ", " << p.second << ")" << endl;
}
void g(pair<T, T> p) {
cout <<"g(" << p.first << ", " << p.second << ")" << endl;
}
};
int main() {
B<int> b;
b.f(make_pair(1, 2));
b.g(make_pair(1, 2));
}
爲什麼不把它編譯?它抱怨B::f()
方法的部分。它似乎沒有認出類A<T>
中的typedef。如果我將T
更改爲具體的類型,它可以工作。完整的錯誤消息如下:
g++ -DNDEBUG -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp"
../main.cpp:13: error: ‘template<class T> struct A’ used without template parameters
../main.cpp:13: error: expected ‘,’ or ‘...’ before ‘p’
../main.cpp: In member function ‘void B<T>::f(int)’:
../main.cpp:14: error: ‘p’ was not declared in this scope
../main.cpp: In function ‘int main()’:
../main.cpp:23: error: no matching function for call to ‘B<int>::f(std::pair<int, int>)’
../main.cpp:13: note: candidates are: void B<T>::f(int) [with T = int]
make: *** [main.o] Error 1
我甚至嘗試了另一種方式,但它仍然沒有奏效:
void f(A::PairType<T> p) {
cout << "f(" << p.first << ", " << p.second << ")" << endl;
}
怎麼會這樣的代碼才能起作用?
可能重複。爲什麼不編譯?](http://stackoverflow.com/questions/5204004/member-template-function-why-doesnt-this-compile) – Jon 2011-03-06 16:20:25
可能的重複[Where to put the「template」and「typename 「在依賴名稱](http://stackoverflow.com/questions/610245/where-to-put-the-template-and-typename-on-dependent-names) – fredoverflow 2011-03-06 16:31:59