C++编程思想 第2卷 第5章 深入理解模板 名称查找问题 模板中的名称

当编译器碰到一个标识符时
它必须能够确定这个标识符所代表的实体的类型和作用域

//: C05:Lookup.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Only produces correct behavior with EDG,
// and Metrowerks using a special option.
#include <iostream>
using std::cout;
using std::endl;

void f(double) { cout << "f(double)" << endl; }

template<class T> class X {
public:
  void g() { f(1); }
};

void f(int) { cout << "f(int)" << endl; }

int main() {
  X<int>().g();
  getchar();
} ///:~

输出
f(int)

在实际的应用系统中存在大量的依赖非标准行为的不规范代码
即使g()中f(1)的调用与其后的f(int)绑定在了一起
编译器的编写者不情愿的改动

//: C05:Lookup2.cpp {-bor}{-g++}{-dmc}
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Microsoft: use option -Za (ANSI mode)
#include <algorithm>
#include <iostream>
#include <typeinfo>
using std::cout;
using std::endl;

void g() { cout << "global g()" << endl; }

template<class T> class Y {
public:
  void g() {
    cout << "Y<" << typeid(T).name() << ">::g()" << endl;
  }
  void h() {
    cout << "Y<" << typeid(T).name() << ">::h()" << endl;
  }
  typedef int E;
};

typedef double E;

template<class T> void swap(T& t1, T& t2) {
  cout << "global swap" << endl;
  T temp = t1;
  t1 = t2;
  t2 = temp;
}

template<class T> class X : public Y<T> {
public:
  E f() {
    g();
    this->h();
    T t1 = T(), t2 = T(1);
    cout << t1 << endl;
    swap(t1, t2);
    std::swap(t1, t2);
    cout << typeid(E).name() << endl;
    return E(t2);
  }
};

int main() {
  X<int> x;
  cout << x.f() << endl;
  getchar();
} ///:~

输出
Y<int>::g()
Y<int>::h()
0
global swap
int
1

若名称是关联的
则它的查找是在实例化时进行
非限定的关联名称除外
它是一个普通名称查找
它的查找进行的比较早是在定义时进行