C++编程思想 第2卷 第6章 通用算法 STL算法目录 实例创建的支持工具

显示一个序列时经常要做的工作
这里有函数模板来打印任意一个序列
不考虑序列中包含的数据类型 

//: C06:PrintSequence.h
// 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.
// Prints the contents of any sequence.
#ifndef PRINTSEQUENCE_H
#define PRINTSEQUENCE_H
#include <algorithm>
#include <iostream>
#include <iterator>

template<typename Iter>
void print(Iter first, Iter last, const char* nm = "",
           const char* sep = "\n",
           std::ostream& os = std::cout) {
  if(nm != 0 && *nm != '\0')
    os << nm << ": " << sep;
  typedef typename 
    std::iterator_traits<Iter>::value_type T;
  std::copy(first, last, 
            std::ostream_iterator<T>(std::cout, sep));
  os << std::endl;
}
#endif // PRINTSEQUENCE_H ///:~

以一个换行符 n 作为分隔符
这个函数模板向cout输出
但可以通过修改默认参数来改变它
为了证明对一个序列进行重新排序的算法是稳定性算法还是不稳定性算法
我们需要一些方法来保持对元素的原始位置的跟踪

//: C06:NString.h
// 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.
// A "numbered string" that keeps track of the
// number of occurrences of the word it contains.
#ifndef NSTRING_H
#define NSTRING_H
#include <algorithm>
#include <iostream>
#include <string>
#include <utility>
#include <vector>

typedef std::pair<std::string, int> psi;

// Only compare on the first element
bool operator==(const psi& l, const psi& r) {
  return l.first == r.first;
}

class NString {
  std::string s;
  int thisOccurrence;
  // Keep track of the number of occurrences:
  typedef std::vector<psi> vp;
  typedef vp::iterator vpit;
  static vp words;
  void addString(const std::string& x) {
    psi p(x, 0);
    vpit it = std::find(words.begin(), words.end(), p);
    if(it != words.end())
      thisOccurrence = ++it->second;
    else {
      thisOccurrence = 0;
      words.push_back(p);
    }
  }
public:
  NString() : thisOccurrence(0) {}
  NString(const std::string& x) : s(x) { addString(x); }
  NString(const char* x) : s(x) { addString(x); }
  // Implicit operator= and copy-constructor are OK here.
  friend std::ostream& operator<<(
    std::ostream& os, const NString& ns) {
    return os << ns.s << " [" << ns.thisOccurrence << "]";
  }
  // Need this for sorting. Notice it only
  // compares strings, not occurrences:
  friend bool
  operator<(const NString& l, const NString& r) {
    return l.s < r.s;
  }
  friend
  bool operator==(const NString& l, const NString& r) {
    return l.s == r.s;
  }
  // For sorting with greater<NString>:
  friend bool
  operator>(const NString& l, const NString& r) {
    return l.s > r.s;
  }
  // To get at the string directly:
  operator const std::string&() const { return s; }
};

// Because NString::vp is a template and we are using the
// inclusion model, it must be defined in this header file:
NString::vp NString::words;
#endif // NSTRING_H ///:~

无输出 只有头文件

通常使用map容器来将一个与字符串一起出现的数字关联起来
在这里用成对的vector来代替映射
执行有秩序的升序排序必须的运算符只有NString::operator<()