引号中带有逗号的C++CSV解析

CSV格式没有正式的标准，但让我们首先注意你引用的丑陋专栏：

"abc, defghijk. "Lmnopqrs, "tuv,"" wxyz.",

不符合CSV的基本规则，因为其中两个是：-

• 1） 带有嵌入逗号的字段必须加引号。

• 2） 每个嵌入的双引号字符必须由一对双引号字符表示。

如果问题列遵守规则1），那么它就不遵守规则2）。但我们可以理解以便遵守规则1）-因此我们可以说它的结束位置-如果我们平衡双引号，例如

[abc, defghijk. [Lmnopqrs, ]tuv,[] wxyz.],

最外面的平衡引号将列括起来。平衡的内部报价除了平衡之外，可能没有任何其他内部迹象使它们内部化。

我们想要一个规则，将此文本解析为一列，与规则1一致），并且还将解析也要遵守规则2）。刚刚展示的平衡表明可以做到，因为遵守这两个规则的列必然是平衡能力也很强。

建议的规则是：

• 列运行到前面有0个双引号的第一个逗号或前面是偶数个双引号中的最后一个

如果逗号前有偶数个双引号，那么我们就知道我们可以至少用一种方法来平衡附引号和其他引号。

您正在考虑的更简单的规则：

在遇到引用后，我应该逐个阅读引用的垃圾字符，直到我找到"，按顺序？

如果遇到不遵守规则2）的某些列，将失败，例如

"超级"豪华"卡车"

更简单的规则将在""luxurious""之后终止列。但自从该列符合规则2），相邻的双引号为"转义"双引号-引号，没有定界意义。另一方面，建议规则仍然正确地解析列，在truck"之后终止它。

下面是一个演示程序，其中函数get_csv_column解析列按照建议的规则：

#include <iostream>
#include <fstream>
#include <cstdlib>  
using namespace std;
/*
    Assume `in` is positioned at start of column.
    Accumulates chars from `in` as long as `in` is good
    until either:-
        - Have consumed a comma preceded by 0 quotes,or
        - Have consumed a comma immediately preceded by
        the last of an even number of quotes.
*/
std::string get_csv_column(ifstream & in)
{
    std::string col;
    unsigned quotes = 0;
    char prev = 0;
    bool finis = false;
    for (int ch; !finis && (ch = in.get()) != EOF; ) {
        switch(ch) {
        case '"':
            ++quotes;
            break;
        case ',':
            if (quotes == 0 || (prev == '"' && (quotes & 1) == 0)) {
                finis = true;
            }
            break;
        default:;
        }
        col += prev = ch;
    }
    return col;
}
int main()
{
    ifstream in("csv.txt");
    if (!in) {
        cout << "Open error :(" << endl;
        exit(EXIT_FAILURE);
    }
    for (std::string col; in; ) {
        col = get_csv_column(in),
        cout << "<[" << col << "]>" << std::endl;
    }
    if (!in && !in.eof()) {
        cout << "Read error :(" << endl;
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

它包含<[...]>中的每一列，不包括换行符，并且包括终端"，"，每列：

文件csv.txt为：

...,"abc, defghijk. "Lmnopqrs, "tuv,"" wxyz.",...,
",","",
Year,Make,Model,Description,Price,
1997,Ford,E350,"Super, ""luxurious"", truck",
1997,Ford,E350,"Super, ""luxurious"" truck",
1997,Ford,E350,"ac, abs, moon",3000.00,
1999,Chevy,"Venture ""Extended Edition""","",4900.00,
1999,Chevy,"Venture ""Extended Edition, Very Large""",,5000.00,
1996,Jeep,Grand Cherokee,"MUST SELL!
air, moon roof, loaded",4799.00,

输出为：

<[...,]>
<["abc, defghijk. "Lmnopqrs, "tuv,"" wxyz.",]>
<[...,]>
<[
",",]>
<["",]>
<[
Year,]>
<[Make,]>
<[Model,]>
<[Description,]>
<[Price,]>
<[
1997,]>
<[Ford,]>
<[E350,]>
<["Super, ""luxurious"", truck",]>
<[
1997,]>
<[Ford,]>
<[E350,]>
<["Super, ""luxurious"" truck",]>
<[
1997,]>
<[Ford,]>
<[E350,]>
<["ac, abs, moon",]>
<[3000.00,]>
<[
1999,]>
<[Chevy,]>
<["Venture ""Extended Edition""",]>
<["",]>
<[4900.00,]>
<[
1999,]>
<[Chevy,]>
<["Venture ""Extended Edition, Very Large""",]>
<[,]>
<[5000.00,]>
<[
1996,]>
<[Jeep,]>
<[Grand Cherokee,]>
<["MUST SELL!
air, moon roof, loaded",]>
<[4799.00]>

这是c++中最优雅的读取.csv文件的方法，该文件中带有引号（即引号）的标记内有逗号：

std::string                           header;
std::vector<std::vector<std::string>> cSVRows;
std::ifstream                         reader(fileName);
if (reader.is_open()) {
    std::string line, column, id;
    std::getline(reader, line);
    header = line;
    while (std::getline(reader, line)) {
        std::stringstream        ss(line);
        std::vector<std::string> columns;
        bool                     withQ = false;
        std::string              part{""};
        while (std::getline(ss, column, ',')) {
            auto pos = column.find(""");
            if (pos < column.length()) {
                withQ = !withQ;
                part += column.substr(0, pos);
                column = column.substr(pos + 1, column.length());
            }
            if (!withQ) {
                column += part;
                columns.emplace_back(std::move(column));
                part = "";
            } else {
                part += column + ",";
            }
        }
        cSVRows.emplace_back(columns);
    }
}