学步园

Objects of class types that define the call operator are often referred to as function objects that is, they are objects that act like functions.（定义了调用操作符
的类，其对象常称为函数对象
，即它们是行为类似函数
的对象。）

定义BET_cls类，用于测试给定string对象的长度是否与其边界相匹配；
定义GT_cls类，用于测试给定string对象的长度是否在给定值以上；
读入文本文件，使用BET_cls类和GT_cls类，统计长度在1到9之间（含1和9）及10以上的单词的数目（排除相同的单词）。

[1]
使用自己定义的函数对象类
，BET_cls和GT_cls

#include <iostream><br /> #include <fstream><br /> #include <vector><br /> #include <algorithm><br /> #include <string><br /> using namespace std;<br /> #define LOCAL<br /> class BET_cls<br /> {<br /> public:<br /> BET_cls(string::size_type len1, string::size_type len2)<br /> {<br /> if (len1<len2)<br /> {<br /> minLength=len1;<br /> maxLength=len2;<br /> }<br /> else<br /> {<br /> minLength=len2;<br /> maxLength=len1;<br /> }<br /> }<br /> bool operator() (const string &s)<br /> {<br /> return s.size()>=minLength && s.size()<=maxLength;<br /> }<br /> private:<br /> string::size_type minLength, maxLength;<br /> };<br /> class GT_cls<br /> {<br /> public:<br /> GT_cls(size_t val=0):bound(val) {}<br /> bool operator() (const string &s)<br /> {<br /> return s.size()>=bound;<br /> }<br /> private:<br /> string::size_type bound;<br /> };<br /> bool isShorter(const string &s1, const string &s2)<br /> {<br /> return s1.size()<s2.size();<br /> }<br /> string make_plural(size_t ctr, const string &word, const string &ending)<br /> {<br /> return (ctr==1) ? word : word+ending;<br /> }<br /> int main(int argc, char* argv[])<br /> {<br /> #ifdef LOCAL<br /> freopen("output.txt", "a+", stdout);<br /> #endif<br /> if (argc<2)<br /> {<br /> cerr<<"No input file!"<<endl;<br /> return EXIT_SUCCESS;<br /> }<br /> ifstream inFile;<br /> inFile.open(argv[1]);<br /> if (!inFile)<br /> {<br /> cerr<<"Can not open input file!"<<endl;<br /> return EXIT_SUCCESS;<br /> }<br /> vector<string> words;<br /> string word;<br /> while (inFile>>word)<br /> {<br /> words.push_back(word);<br /> }<br /> sort(words.begin(), words.end());<br /> words.erase(unique(words.begin(), words.end()), words.end());<br /> vector<string>::size_type wc=0;<br /> wc=count_if(words.begin(), words.end(), BET_cls(1, 9));<br /> cout<<wc<<" "<<make_plural(wc, "word", "s")<br /> <<" are of sizes 1 through 9 inclusive"<<endl;<br /> wc=count_if(words.begin(), words.end(), GT_cls(10));<br /> cout<<wc<<" "<<make_plural(wc, "word", "s")<br /> <<" 10 characters or longer"<<endl;<br /> return 0;<br /> }<br /> /*<br /> In Anhui province , 560,000 students will take the exams , but only 240,000 will gain places at University .<br /> Competition is fierce ! You must shoulder your parent's expectations ,<br /> the great trust of your school and the hopes of our Motherland !<br /> output:<br /> 32 words are of sizes 1 through 9 inclusive<br /> 4 words 10 characters or longer<br /> */<br />

[2]
改为使用标准库函数对象
代替GT_cls来查找指定长度的单词
[注意]
因为没有可用于直接比较字符串长度的标准库函数对象，所以不能直接使用count_if算法，改用greater_equal对象
循环实现单词计数。

#include <iostream><br /> #include <fstream><br /> #include <vector><br /> #include <algorithm><br /> #include <string><br /> #include <functional>// note, this header includes the std function objects<br /> using namespace std;<br /> #define LOCAL<br /> class BET_cls<br /> {<br /> public:<br /> BET_cls(string::size_type len1, string::size_type len2)<br /> {<br /> if (len1<len2)<br /> {<br /> minLength=len1;<br /> maxLength=len2;<br /> }<br /> else<br /> {<br /> minLength=len2;<br /> maxLength=len1;<br /> }<br /> }<br /> bool operator() (const string &s)<br /> {<br /> return s.size()>=minLength && s.size()<=maxLength;<br /> }<br /> private:<br /> string::size_type minLength, maxLength;<br /> };<br /> class GT_cls<br /> {<br /> public:<br /> GT_cls(size_t val=0):bound(val) {}<br /> bool operator() (const string &s)<br /> {<br /> return s.size()>=bound;<br /> }<br /> private:<br /> string::size_type bound;<br /> };<br /> bool isShorter(const string &s1, const string &s2)<br /> {<br /> return s1.size()<s2.size();<br /> }<br /> string make_plural(size_t ctr, const string &word, const string &ending)<br /> {<br /> return (ctr==1) ? word : word+ending;<br /> }<br /> int main(int argc, char* argv[])<br /> {<br /> #ifdef LOCAL<br /> freopen("output.txt", "a+", stdout);<br /> #endif<br /> if (argc<2)<br /> {<br /> cerr<<"No input file!"<<endl;<br /> return EXIT_SUCCESS;<br /> }<br /> ifstream inFile;<br /> inFile.open(argv[1]);<br /> //inFile.open("1.txt");<br /> if (!inFile)<br /> {<br /> cerr<<"Can not open input file!"<<endl;<br /> return EXIT_SUCCESS;<br /> }<br /> vector<string> words;<br /> string word;<br /> while (inFile>>word)<br /> {<br /> words.push_back(word);<br /> }<br /> sort(words.begin(), words.end());<br /> words.erase(unique(words.begin(), words.end()), words.end());<br /> vector<string>::size_type wc=0;<br /> wc=count_if(words.begin(), words.end(), BET_cls(1, 9));// std has not this function object<br /> cout<<wc<<" "<<make_plural(wc, "word", "s")<br /> <<" are of sizes 1 through 9 inclusive"<<endl;<br /> //wc=count_if(words.begin(), words.end(), GT_cls(10));// my function object<br /> //wc=count_if(words.begin(), words.end(), bind2nd(greater<string>(), 10));// error</p> <p> // the following way is right !<br /> wc=0;<br /> greater_equal<string::size_type> grep;// std function object<br /> for (vector<string>::const_iterator iter=words.begin(); iter!=words.end(); ++iter)<br /> {<br /> if (grep(iter->size(), 10))<br /> ++wc;<br /> }<br /> cout<<wc<<" "<<make_plural(wc, "word", "s")<br /> <<" 10 characters or longer"<<endl;<br /> return 0;<br /> }<br /> /*<br /> In Anhui province , 560,000 students will take the exams , but only 240,000 will gain places at University .<br /> Competition is fierce ! You must shoulder your parent's expectations ,<br /> the great trust of your school and the hopes of our Motherland !<br /> output:<br /> 32 words are of sizes 1 through 9 inclusive<br /> 4 words 10 characters or longer<br /> */<br />