isalnum的使用

isalnum的函数功能是指出一个字符在运行时字符集中是否为字母数字。也就是这个函数可以帮我们快速判断一个字符是不是字母或数字，而不是其它标点或字符。

使用isalnum需要包含<local>头文件

isalnum第一个参数为需要判断的字符,第二参数为locale("")

运用这个函数，我们可以完成单词统计功能，在有标点的情况下也不怕

 

EXAMPLE

 

#include <iostream>

#include <istream>

#include <ostream>

#include <map>

#include <string>

#include <iomanip>

#include <locale>

int main()

{

 using namespace std;

 map<string,int> counts;

 string word;

 //从标准输入读取单词，并计算每个单词现的次数

 

 while(cin >> word)

 {

  string copy;

  for(string::iterator w(word.begin()); w != word.end(); ++w)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

   if(isalnum(*w,locale()))  //判断是否为字母或数字

    copy.push_back(*w);

   else

   {

    if(! copy.empty())

    ++counts[copy];

    copy.clear();

   }

  if(! copy.empty())

   ++counts[copy];

 }

 int longest(0);

 for(map<string,int>::iterator iter(counts.begin()); iter != counts.end(); ++iter)

 {

  if(iter->first.size() > longest)   //取得单词中最长的一个的长度

   longest = iter->first.size();

 }

 const int count_size(10);

 for(map<string,int>::iterator iter(counts.begin()); iter != counts.end(); ++iter)

  cout<< setw(longest) << left <<iter->first    //以一定的格式输出

   << "\t"

   << setw(count_size) << right << iter->second << "\n";

 map<string,int>::iterator the(counts.find("as"));

 if(the == counts.end())

  cout<< "the not found!\n";

 else

 {

  cout<< "the occurs " << the->second << " times!\n";

 }

}

POSSIBLE OUTPUT