C++ - 从文件读取双倍
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C++ - Read from file to double
提问by Danieboy
I'm relatively new to programming and taking a course in C++ currently. I haven't had any major problems so far. I am making a program where an X amount judges can score 0.0 - 10.0 (double) and then the highest and lowest one is removed then an average is calculated and printed out.
我目前对编程和学习 C++ 课程比较陌生。到目前为止，我还没有遇到任何重大问题。我正在制作一个程序，其中 X 数量的裁判可以得分 0.0 - 10.0（双倍），然后删除最高和最低的一个，然后计算并打印出平均值。
This part is done, now I want to read from a file in the shape of: example.txt - 10.0 9.5 6.4 3.4 7.5
这部分完成了，现在我想从一个文件中读取：example.txt - 10.0 9.5 6.4 3.4 7.5
But I am stumbling onto problems with the dot (.) and how to get around it to get the number into a double. Any suggestions and (good) explanations so I can understand it?
但是我遇到了点 (.) 的问题以及如何绕过它以将数字变为双精度。任何建议和（好的）解释，以便我理解它？
TL;DR: Reading from file (E.G. '9.7') to a double variable to put into an array.
TL;DR：从文件（EG '9.7'）读取到一个双变量以放入一个数组。
回答by jrd1
Since your textfile is whitespace delimited, you can use that to your advantage by utilizing std::istreamobjects who skip whitespace by default (in this case, std::fstream):
由于您的文本文件是空格分隔的，因此您可以利用std::istream默认情况下跳过空格的对象（在本例中为std::fstream）来利用它：
#include <fstream>
#include <vector>
#include <cstdlib>
#include <iostream>
int main() {
std::ifstream ifile("example.txt", std::ios::in);
std::vector<double> scores;
//check to see that the file was opened correctly:
if (!ifile.is_open()) {
std::cerr << "There was a problem opening the input file!\n";
exit(1);//exit or do additional error checking
}
double num = 0.0;
//keep storing values from the text file so long as data exists:
while (ifile >> num) {
scores.push_back(num);
}
//verify that the scores were stored correctly:
for (int i = 0; i < scores.size(); ++i) {
std::cout << scores[i] << std::endl;
}
return 0;
}
Note:
笔记：
It is highly recommended to use vectorsin lieu of dynamic arrays where possible for a myriad number of reasons as discussed here:
强烈建议vectors在可能的情况下使用动态数组代替动态数组，原因如下所述：
回答by kmort
Try this:
尝试这个：
#include <iostream>
#include <fstream>
int main()
{
std::ifstream fin("num.txt");
double d;
fin >> d;
std::cout << d << std::endl;
}
Does that do what you want?
这样做你想要的吗？
