c++ - 迭代器应该读取一个完整的数字，但它只读取第一个数字

Question

我编写这段代码是为了使用字符串迭代器从字符串中提取数字。迭代器选取第一个数字并决定收工。为什么会这样？

    #include <iostream>
#include <string>
#include <sstream>
using namespace std;

int main()
{
 string myAge = "I am 23 years old";
 string::iterator iterator;
 char numberInCharacterForm;
 string numberInStringForm;
 stringstream convertToString;
 for(iterator = myAge.begin();iterator!=myAge.end();iterator++)
 {
              numberInCharacterForm = *iterator;
              if(numberInCharacterForm >= '0' & numberInCharacterForm <='9')
              {
               convertToString << numberInCharacterForm;
               convertToString >> numberInStringForm;
              }
 } 
 cout << numberInStringForm <<endl;   
 getch();
 return 0;
}

输出为2；

Answer 1

只需将字符收集到 stringstream 中，然后打印出来:

for(iterator = myAge.begin();iterator!=myAge.end();iterator++)
{
    numberInCharacterForm = *iterator;
    if(numberInCharacterForm >= '0' && numberInCharacterForm <='9') {
       // note: && instead of & here ^
       convertToString << numberInCharacterForm;
    }
 }   
 cout << convertToString.str() <<endl;   

但是不需要对字符串进行手动迭代:

string myAge = "I am 23 years old"; 
string numberInStringForm;
std::remove_copy_if(myAge.begin(), myAge.end(), 
                    std::back_inserter(numberInStringForm),
                    std::not1(std::ptr_fun(isdigit)));
std::cout << numberInStringForm << std::endl;