在 C++ 中使用 ifstream 逐行读取文件 [英] Read file line by line using ifstream in C++
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++?
我可以获取第一行,但如何获取文件的下一行?
I am able to get the first line, but how do I get the next line of the file?
ifstream myfile;
myfile.open ("file.txt");
推荐答案
首先,制作一个ifstream
:
#include <fstream>
std::ifstream infile("thefile.txt");
两种标准方法是:
假设每一行由两个数字组成并逐个标记读取:
Assume that every line consists of two numbers and read token by token:
int a, b;
while (infile >> a >> b)
{
// process pair (a,b)
}
基于行的解析,使用字符串流:
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)
}
您不应该混合 (1) 和 (2),因为基于令牌的解析不会吞噬换行符,因此如果您使用 getline()
在基于令牌的提取已经让你到达一行的末尾之后.
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.
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