c++ - 从文件读取到 vector C++ 的函数

Question

我编写了一个函数，可以将未知数量的数据(当在列中时)从文件读取到 vector 。

#include <iostream>
#include <vector>
#include <fstream> // file writing
#include <cassert>


void ReadFromFile(std::vector<double> &x, const std::string &file_name)
{
    std::ifstream read_file(file_name);
    assert(read_file.is_open());

    size_t lineCount = 0;
    while (!read_file.eof())
    {
        double temp;
        read_file >> temp;
        x.at(lineCount) = temp;
        if (lineCount == x.size() - 1) { break; } // fixes the out of range exception

        lineCount++;
    }
    read_file.close();
}
int main()
{
    size_t Nx = 7;
    size_t Ny = 7;
    size_t Nz = 7;
    size_t N = Nx*Ny*Nz;

    // Initial Arrays 
    std::vector <double> rx(N);
    std::string Loadrx = "Loadrx.txt";
    ReadFromFile(rx, Loadrx);
}

但是在文件中的数据被复制到 vector 中之后，lineCount 会额外增加一次。有没有比我编写的 if 语句更优雅的方法来解决这个问题？

Answer 1

I have written a function that reads an unknown number of data (when in a column) from a file to a vector.

从“列”(或其他常规范式的)文件中读取未知数量数据的最优雅(而且我想也是惯用的)方法之一是使用 istream 迭代器:

void ReadFromFile(std::vector<double> &x, const std::string &file_name)
{
    std::ifstream read_file(file_name);
    assert(read_file.is_open());

    std::copy(std::istream_iterator<double>(read_file), std::istream_iterator<double>(),
        std::back_inserter(x));

    read_file.close();
}

用法:

int main()
{
    // Note the default constructor - we are constructing an initially empty vector.
    std::vector<double> rx;
    ReadFromFile(rx, "Loadrx.txt");
}

如果你想写一个“安全”的版本来读取有限数量的元素，使用copy_if:

void ReadFromFile(std::vector<double> &x, const std::string &file_name, unsigned int max_read)
{
    std::ifstream read_file(file_name);
    assert(read_file.is_open());

    unsigned int cur = 0;
    std::copy_if(std::istream_iterator<double>(read_file), std::istream_iterator<double>(),
    std::back_inserter(x), [&](const double&) {
        return (cur++ < max_read);
    });

    read_file.close();
}

用法很明显:

ReadFromFile(rx, Loadrx, max_numbers);