在C ++中使用ifstream逐行读取文件

问题描述

file.txt的内容为:

The contents of file.txt are:

5 3
6 4
7 1
10 5
11 6
12 3
12 4

其中5 3是坐标对.如何在C ++中逐行处理此数据?

Where 5 3 is a coordinate pair.How do I process this data line by line in C++?

我能够获得第一行，但是如何获得文件的下一行?

I am able to get the first line, but how do I get the next line of the file?

ifstream myfile;
myfile.open ("text.txt");

推荐答案

首先，创建一个ifstream:

#include <fstream>
std::ifstream infile("thefile.txt");

两种标准方法是:

1. 假设每行包含两个数字，并逐个令牌读取令牌:

1. Assume that every line consists of two numbers and read token by token:

int a, b;
while (infile >> a >> b)
{
    // process pair (a,b)
}

使用字符串流的基于行的解析:

Line-based parsing, using string streams:

#include <sstream>
#include <string>

std::string line;
while (std::getline(infile, line))
{
    std::istringstream iss(line);
    int a, b;
    if (!(iss >> a >> b)) { break; } // error

    // process pair (a,b)
}

您不应混用(1)和(2)，因为基于令牌的解析不会占用换行符，因此如果在基于令牌的提取后使用getline()，可能会导致虚假的空行您已经到行尾了.

You shouldn't mix (1) and (2), since the token-based parsing doesn't gobble up newlines, so you may end up with spurious empty lines if you use getline() after token-based extraction got you to the end of a line already.

这篇关于在C ++中使用ifstream逐行读取文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！