std::getline 部分读取第一行和最后一行以及位集答案

【问题标题】：std::getline partially reads first and last line and sets eof-bitstd::getline 部分读取第一行和最后一行以及位集
【发布时间】：2015-07-18 01:09:22
【问题描述】：

我需要用 C++ 读取 csv 文件：文件的第一行包含所有列标题，其余行包含浮点数据（以下示例，文件已被缩小）。

一些文件有问题，我正在使用以下代码

#include <iostream>
#include <fstream>
#include <string>

// Compiled and testen on with Clang++ on Ubuntu 14.04
int main(int argc, char** argv) {
    std::ifstream in;
    in.open(argv[1]);

    if(!in.is_open()) {
        std::cerr << "Cannot open file: " << argv[1] << "\n";
        return 1;
    }

    std::string buff;
    std::getline(in, buff);
    while(!in.eof()) {
        std::cout << buff << "\n";
        getline(in, buff);
    }

    in.close();
    return 0;
}

对于大多数文件，这运行正常，每次迭代读取一行； “好”文件的示例：

Time,Smile,AU04,AU02,AU15,Trackerfail,AU18,AU09,negAU12,AU10,Expressive,Unilateral_LAU12,Unilateral_RAU12,AU14,Unilateral_LAU14,Unilateral_RAU14,AU05,AU17,AU26,Forward,Backward
0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,33.333,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,20.0
0.3,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,33.333,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0
1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,33.333,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,16.667,0.0
58.3,50.0,0.0,0.0,0.0,33.333,0.0,0.0,0.0,0.0,100.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0
62.4,33.333,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,100.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,20.0

有些文件会发疯，并在第一个 getline 之后设置 eof 位。在第一次读取之后，buff 包含第一行的一部分和最后一行的一部分； “坏”文件的示例：

Time,Smile,AU04,AU02,AU15,Trackerfail,AU18,AU09,negAU12,AU10,Occlusion,Expressive,Unilateral_LAU12,Unilateral_RAU12,AU14,Unilateral_LAU14,Unilateral_RAU14,AU05,Au17,AU57,AU58
0,0,0,0,0,16.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
0.3,0,0,0,0,33.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
1.3,0,0,0,0,16.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
57.9,66.667,0,0,0,66.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
60.3,33.333,0,0,0,66.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

和buff的内容在一次调用getline之后：

Time,Smile,AU04,AU02,AU15,Trackerfail,AU18,AU09,negAU12,AU10,Occlusion,Expressive,Unilateral_LAU12,Unilateral_RAU12,AU14,Unilateral_LAU14,Unilateral_RA60.3,33.333,0,0,0,66.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

如您所见，第一行与最后一行混合在一起。我不知道出了什么问题。每行以\n 结尾，文件以空\n 结尾。

我想我的问题是：为什么getline 会跳到文件结尾，同时将某些文件的第一行和最后一行混合在一起，而其他文件却可以正常工作？

编辑：我需要将一个大数据集转换为一种新的、更一致的格式。当前格式充满了不一致（使用0 和0.0 或AU17 和Au17）。不过，这些格式问题应该不会影响简单地读取文件，对吧？

编辑2：

cat -v -e -t 在一个好文件上：

Time,Smile,AU04,AU02,AU15,Trackerfail,AU18,AU09,negAU12,AU10,Expressive,Unilateral_LAU12,Unilateral_RAU12,AU14,Unilateral_LAU14,AU05,AU17,AU26,Forward,Backward^M$
0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,66.667,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0^M$
0.2,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,33.333,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0^M$
etc...

cat -v -e -t 在错误文件上：

Time,Smile,AU04,AU02,AU15,Trackerfail,AU18,AU09,negAU12,AU10,Occlusion,Expressive,Unilateral_LAU12,Unilateral_RAU12,AU14,Unilateral_LAU14,Unilateral_RAU14,AU05,Au17,AU57,AU58^M0,0,0,0,0,16.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M0.3,0,0,0,0,33.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M1.3,0,0,0,0,16.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M1.4,0,0,0,0,33.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M1.8,0,0,0,0,50,0,0,0,0,0,0,0,0,0,0,0,0,0,25,0^M2.8,0,0,0,0,50,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M3,0,0,0,0,33.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M31,0,0,0,0,33.333,0,0,0,0,25,0,0,0,0,0,0,0,0,0,0^M31.1,0,0,0,0,50,0,0,0,0,50,0,0,0,0,0,0,0,0,0,0^M31.2,0,0,0,0,66.667,0,0,0,0,50,0,0,0,0,0,0,0,0,0,0^M31.4,0,0,33.333,0,66.667,0,0,0,0,50,0,0,0,0,0,0,0,0,0,0^M31.5,0,0,33.333,0,66.667,0,0,0,0,50,25,0,0,0,0,0,0,0,0,0^M32,0,0,33.333,0,66.667,0,0,0,0,50,25,0,0,0,0,0,0,0,0,25^M32.1,0,0,33.333,0,83.333,0,0,0,0,50,25,0,0,0,0,0,0,0,0,25^M32.2,0,0,33.333,0,83.333,0,0,0,0,25,25,0,0,0,0,0,0,0,0,25^M32.4,0,0,33.333,0,83.333,0,0,0,0,25,0,0,0,0,0,0,0,0,0,25^M32.7,0,0,33.333,0,83.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,25^M33,0,0,33.333,0,83.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M33.5,0,0,0,0,83.333,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M33.9,0,0,0,0,66.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M55,33.333,0,0,0,66.667,0,0,0,0,0,25,0,0,0,0,0,0,0,0,0^M55.2,66.667,0,0,0,66.667,0,0,0,0,0,25,0,0,0,0,0,0,0,0,0^M55.8,100,0,0,0,66.667,0,0,0,0,0,25,0,0,0,0,0,0,0,0,0^M56.8,100,0,0,0,66.667,0,0,0,0,0,25,0,0,0,0,0,0,0,0,25^M57.4,66.667,0,0,0,66.667,0,0,0,0,0,25,0,0,0,0,0,0,0,0,25^M57.8,66.667,0,0,0,66.667,0,0,0,0,0,25,0,0,0,0,0,0,0,0,0^M57.9,66.667,0,0,0,66.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0^M60.3,33.333,0,0,0,66.667,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

看起来差别很大，我该如何解决？

【问题讨论】：

与您的问题无关，但不是两个 std::getline 调用，为什么不简单地依赖 std::getline （就像几乎所有其他流函数一样）返回实际的流引用，并执行例如while (std::getline(...))?
至于你的问题，你确定文件没有其他问题吗？您只检查文件结尾而不是循环中的其他错误。错误文件中没有隐藏（不可打印）字符？相同的文件总是有问题吗？
@JoachimPileborg 在这段代码的 sn-p 中出现这种情况的原因是我想快速检查不同的位：eof、fail、bad。但是在我的应用程序代码中，我正在按照您的建议进行操作。 编辑： 它永远不会到达循环内部，立即设置 eof-bit；检查失败位会导致单次迭代。是的，它总是在同一个文件上，这让人非常好奇！我检查了 \r 和 \c 字符，但文件中没有。
cat -v -e -t <your_file> 的输出是什么？我怀疑@Joachim Pileborg 是正确的。
您在 Windows 上吗？因为如果文本中有 CTRL-Z（ASCII 0x1a），它也将充当文件结尾。您是否在十六进制编辑器中检查过文件？

标签： c++ csv eof getline

【解决方案1】：

文件似乎缺少换行符，而只有回车符（等于 ^M 或 CTRLM）。

您可以通过对文件使用cat 来修复它，并通过管道传递到tr 以将回车转换为换行符：

$ cat your-file | tr '\r' '\n' > your-file-fixed

在看到您对来自 Max OS 的文件的评论后，我认为这是旧的 pre-OSX 版本，当时 Mac OS 上的换行符只是一个回车。

【讨论】：

根据 Sublime Text，它们是在 Mac OS 9 上制作的。再次感谢您的帮助！