使用C ++ ifstream从文本文件读取整数 [英] Read integers from a text file with C++ ifstream
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问题描述
我想从文本文件中读取图形邻接信息并将其存储到向量中。
-
行数
-
每行都有以'\\\
'结尾的任意数字整数
例如,
第一行:
0 1 4
第二行:
1 0 4 3 2
第三行:
2 1 3
第四行:
3 1 2 4
第五行:
4 0 1 3
如果我使用getline
有没有建议?
解决方案
标准行阅读习语:
#include< fstream&
#include< sstream>
#include< string>
#include< vector>
std :: ifstream infile(thefile.txt);
std :: string line;
while(std :: getline(infile,line))
{
std :: istringstream iss(line);
int n;
std :: vector< int> v;
while(iss>> n)
{
v.push_back(n);
}
//对v
使用有用的操作
$ b
$ b b
这是一个单行版本,使用来循环
。我们需要一个辅助结构(信用@ @ Luc Danton !)与 std :: move
:
命名空间std
{
template<类型名T> T&留(t& t){return t; }
}
int main()
{
std :: vector< std :: vector< int> vv;
for(std :: string line;
std :: getline(std :: cin,line);
vv.push_back(std :: vector< int> :: istream_iterator< int>(std :: stay(std :: istringstream(line))),
std :: istream_iterator< int>())
)
){}
std :: cout<< vv< std :: endl;
}
I want to read graph adjacency information from a text file and store it into a vector.
the file has arbitrary number of lines
each line has arbitrary number of integers ended with '\n'
for example,
First line:
0 1 4
Second line:
1 0 4 3 2
Thrid line:
2 1 3
Fourth line:
3 1 2 4
Fifth line:
4 0 1 3
If I use getline() to read one line at a time, how do I parse the line (as each line has variable number of integers)?
Any suggestions?
解决方案
The standard line reading idiom:
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
std::ifstream infile("thefile.txt");
std::string line;
while (std::getline(infile, line))
{
std::istringstream iss(line);
int n;
std::vector<int> v;
while (iss >> n)
{
v.push_back(n);
}
// do something useful with v
}
Here's a one-line version using a for
loop. We need an auxiliary construction (credits to @Luc Danton!) that does the opposite of std::move
:
namespace std
{
template <typename T> T & stay(T && t) { return t; }
}
int main()
{
std::vector<std::vector<int>> vv;
for (std::string line;
std::getline(std::cin, line);
vv.push_back(std::vector<int>(std::istream_iterator<int>(std::stay(std::istringstream(line))),
std::istream_iterator<int>())
)
) { }
std::cout << vv << std::endl;
}
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