快速,简单的CSV解析在C ++ [英] Fast, Simple CSV Parsing in C++
问题描述
我试图解析一个简单的CSV文件,数据格式如下:
I am trying to parse a simple CSV file, with data in a format such as:
20.5,20.5,20.5,0.794145,4.05286,0.792519,1
20.5,30.5,20.5,0.753669,3.91888,0.749897,1
20.5,40.5,20.5,0.701055,3.80348,0.695326,1
所以,一个非常简单和固定的格式文件。我将这些数据的每一列存储到一个STL向量中。因此,我试图使用标准库保持C ++的方式,我在循环中的实现看起来像:
So, a very simple and fixed format file. I am storing each column of this data into a STL vector. As such I've tried to stay the C++ way using the standard library, and my implementation within a loop looks something like:
string field;
getline(file,line);
stringstream ssline(line);
getline( ssline, field, ',' );
stringstream fs1(field);
fs1 >> cent_x.at(n);
getline( ssline, field, ',' );
stringstream fs2(field);
fs2 >> cent_y.at(n);
getline( ssline, field, ',' );
stringstream fs3(field);
fs3 >> cent_z.at(n);
getline( ssline, field, ',' );
stringstream fs4(field);
fs4 >> u.at(n);
getline( ssline, field, ',' );
stringstream fs5(field);
fs5 >> v.at(n);
getline( ssline, field, ',' );
stringstream fs6(field);
fs6 >> w.at(n);
问题是,这是非常慢的(每个数据文件有超过100万行)似乎对我来说有点不高兴。有更快的方法使用标准库,或者我应该使用stdio函数?在我看来,整个代码块将减少到单个fscanf调用。
The problem is, this is extremely slow (there are over 1 million rows per data file), and seems to me to be a bit inelegant. Is there a faster approach using the standard library, or should I just use stdio functions? It seems to me this entire code block would reduce to a single fscanf call.
提前感谢!
推荐答案
使用7个字符串流,当你可以做到只用一个肯定不帮助wrt。性能。
尝试这样:
Using 7 string streams when you can do it with just one sure doesn't help wrt. performance. Try this instead:
string line;
getline(file, line);
istringstream ss(line); // note we use istringstream, we don't need the o part of stringstream
char c1, c2, c3, c4, c5; // to eat the commas
ss >> cent_x.at(n) >> c1 >>
cent_y.at(n) >> c2 >>
cent_z.at(n) >> c3 >>
u.at(n) >> c4 >>
v.at(n) >> c5 >>
w.at(n);
如果知道文件中的行数,可以在读取之前调整向量大小,然后请使用 operator []
而不是在()
。这样你避免了边界检查,从而获得一点性能。
If you know the number of lines in the file, you can resize the vectors prior to reading and then use operator[]
instead of at()
. This way you avoid bounds checking and thus gain a little performance.
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