C ++代码获取文件行并读取该行的第二个单词？

Question

#include <iostream>
#include <string>
#include <fstream>

using namespace std ;


string strWord( int index , string line)
{
       int count = 0;
       string word;
       for ( int i = 0 ; i < line.length(); i++)
       {
           if ( line[i] == ' ' )
           {
                if ( line [i+1] != ' ')
                {

                    count ++;
                    if (  count == index)
                    {
                       return word;
                    }
                    word ="";
                }
           }
           else
           {
                word += line[i];
           }       
       }
}







int main ( )
{
    ifstream inFile ;
    inFile.open("new.txt");
    string line  , id;

    cout <<"Enter id : ";
    cin >>id;
    while(!inFile.eof() )
    {
                        getline ( inFile , line );
                        if ( strWord ( 1, line ) == id ) 
                        {
                             cout <<strWord ( 2 , line ) <<endl;
                             break;
                        }
    } 
    system("pause");
}

问题是：有人可以向我解释一下吗？我不明白我在做什么，我的意思是我明白了，但是每一行在做什么？

Answer 1

您想要每行的评论

// function that returns a word from 'line' with position 'index'
// note that this is not a zero based index, first word is 1,
// second is 2 etc ..
string strWord(int index, string line)
{
    int count = 0; // number of read words
    string word; // the resulting word
    for (int i = 0 ; i < line.length(); i++) { // iterate over all characters in 'line'
        if (line[i] == ' ') { // if this character is a space we might be done reading a word from 'line'
            if (line[i+1] != ' ') { // next character is not a space, so we are done reading a word
                count++; // increase number of read words
                if (count == index) { // was this the word we were looking for?
                    return word; // yes it was, so return it
                }
                word =""; // nope it wasn't .. so reset word and start over with the next one in 'line'
            }
        }
        else { // not a space .. so append the character to 'word'
           word += line[i];
        }       
    }
}


int main( ) // main function of the program, execution starts here
{
    ifstream inFile; // construct input file stream object
    inFile.open("new.txt"); // associate the stream with file named "new.txt"
    string line, id; // 

    cout << "Enter id : "; // write "Enter id :" to console
    cin >> id; // read input from console and put the result in 'id'

    while (!inFile.eof()) { // do the following as long as there is something to read from the file
        getline(inFile, line); // read a line from the file and put the value into 'line'
    if (strWord(1, line) == id) { // if the first word in 'line' equals 'id' ..
        cout << strWord(2, line) << endl; // prints the second word in 'line'
        break; // exits the while loop
    }
    } 

    system("pause"); // pause the program (should be avoided)
}

Answer 2

我没有仔细阅读，但是看起来它打印出该行的第二个单词，第一个单词是用户输入的单词。

Answer 3

也许这可以帮助：

// return word[index] from line
string strWord( int index , string line) // word index and actual line
{
  int count = 0; // current word index
  string word; // word buffer (return value)

  for ( int i = 0 ; i < line.length(); i++) // loop through each character in line
  {
    if ( line[i] == ' ' ) // if current character is a space
    {
      if ( line [i+1] != ' ')  // but next char is not space, we got a word
      {
        count ++; // incr current word index counter in line
        if (  count == index) // if count == looked for index return word
        {
          return word;
        }
        word ="";  // otherwise reset word buffer
      }
    }
    else // character is not space
    {
       word += line[i]; // add letter/digit to word buffer
    }       
  }
}

例如，当行以空格开头时，上面的算法将失败，因此此处存在许多需要处理的有关数据中的假设，例如如果索引无效或如果行为空，则不进行任何处理。 如果函数失败，则还会丢失最后一个返回值。

Answer 4

您有用于C ++的交互式调试器吗？ 例如，如果将此代码加载到Microsoft Visual C ++中，则可以一次浏览一个程序语句，同时检查每个变量的值。 这是学习新代码在细节级别上做什么的好方法。

Answer 5

有一个名为strWord的函数，用于从句子中获取带有任何索引的单词并将其返回。

主程序打开一个文件，在每行中包含一个ID和另一个单词，并准备将其读取。

然后，它向用户询问ID，检查该ID是否为文件中任何行中的第一个单词。 如果是，则从该行中提取第二个单词并打印出来。

就这样。 询问您对特定的线或线束是否有问题。

或如Greg建议的那样，去调试器。 这将是理解任何逻辑的最简单方法。