逐行读取文件 [英] Read file line by line
问题描述
file.txt的内容是:
5 3
6 4
7 1
10 5
11 6
12 3
12 4
其中 5 3
是一个坐标对。
如何在C ++中逐行处理这个数据?
我可以得到第一行,但是如何获得第一行文件?
ofstream myfile;
myfile.open(text.txt);
:
#include< fstream&
std :: ifstream infile(thefile.txt);
这两种标准方法是:
-
假设每行由两个数字组成,并通过令牌读取令牌:
int a ,b;
while(infile>> a>> b)
{
// process pair(a,b)
}
-
使用字符串流进行基于行的解析:
#include< sstream>
#include< string>
std :: string line;
while(std :: getline(infile,line))
{
std :: istringstream iss(line);
int a,b;
if(!(iss>> a>> b)){break; } //错误
//进程对(a,b)
}
你不应该混合使用(1)和(2),因为基于令牌的解析不会换行,如果您在使用基于令牌的提取之后使用 getline()
,您就可以使用空行。
The contents of file.txt are:
5 3
6 4
7 1
10 5
11 6
12 3
12 4
Where 5 3
is a coordinate pair.
How do I process this data line by line in C++?
I am able to get the first line, but how do I get the next line of the file?
ofstream myfile;
myfile.open ("text.txt");
First, make an ifstream
:
#include <fstream>
std::ifstream infile("thefile.txt");
The two standard methods are:
Assume that every line consists of two numbers and read token by token:
int a, b; while (infile >> a >> b) { // process pair (a,b) }
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) }
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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