c++ - c++ ifstream行尾

Question

我有一个看起来像这样的文件：

e r g d g d
f h d r h f
..........

我想将这些字符存储在二维数组中

#include <fstream>
#include <iostream>
using namespace std;
int main()
{
    ifstream file("file.txt");
    char c[20][20];
    int i = 0, j = 0;
    while(!file.eof())
    {
        while(!end of line?)
        {
            file >> c[i][j];
            j++;
        }
        i++;
    }
.....
}        

我该怎么做呢？
或者如何查找一行中的字符数？

Answer 1

你不能eof()像你一样使用。您必须先执行 I/O 读取操作，然后才能使用eof().

对于您正在尝试的内容，您应该std::getline()改用，例如：

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <algorithm>

int main()
{
    std::ifstream file("file.txt");
    std::string line;
    char c[20][20] = {};

    for (int i = 0; i < 20; ++i)
    {
        if (!std::getline(file, line))
            break;

        std::istringstream iss(line);
        for(j = 0; j < 20; ++j)
        {
            if (!(iss >> c[i][j]))
                break;
        }
    }

    ...

    return 0;
}

话虽如此，您应该考虑使用std::vector而不是固定大小的数组（除非您知道您的文件永远不会超过 20 行和/或每行 20 个字符）：

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <iterator>
#include <algorithm>
#include <vector>

int main()
{
    std::ifstream file("file.txt");
    std::vector<std::vector<char> > c;
    std::string line;

    while (std::getline(file, line))
    {
        std::istringstream iss(line);
        std::vector<char> tmp;

        std::copy(
            std::istream_iterator<char>(iss),
            std::istream_iterator<char>(),
            std::back_inserter(tmp)
        );

        /* which is equivalent to:
        char ch;
        while (iss >> ch) {
            tmp.push_back(ch);
        }
        */

        c.push_back(tmp);
    }

    ...

    return 0;
}

或者：

#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <iterator>
#include <algorithm>
#include <vector>

typedef std::vector<char> CharVector;

std::istream& operator>>(std::istream &in, CharVector &out)
{
    out.clear();

    std::string line;
    if (std::getline(in, line))
    {
        std::istringstream iss(line);

        std::copy(
            std::istream_iterator<char>(iss),
            std::istream_iterator<char>(),
            std::back_inserter(out)
        );

        /* which is equivalent to:
        char ch;
        while (iss >> ch) {
            out.push_back(ch);
        }
        */
    }

    return in;
}

int main()
{
    std::ifstream file("file.txt");
    std::vector<CharVector> c;

    std::copy(
        std::istream_iterator<CharVector>(file),
        std::istream_iterator<CharVector>(),
        std::back_inserter(c)
    );

    /* which is equivalent to:
    CharVector cv;
    while (file >> cv) {
        c.push_back(cv);
    }
    */

    ...

    return 0;
}