如何从 CSV 获取数据并将其存储在 C++ 中的表对象中

Question

所以基本上我希望能够打开一个CSV文件并根据该文件中的数据构造一个表对象。

以下是数据在 CSV 文件中的外观示例：

year,category,winner,entity
INT,STRING,BOOL,STRING
2015,CHEF OF THE YEAR,FALSE,John Doe
2015,CHEF OF THE YEAR,FALSE,Bob Brown
2015,CHEF OF THE YEAR,TRUE, William Thorton
2015,CHEF OF THE YEAR,FALSE,Jacob Smith

第一行列出表中所有属性的名称，第二行列出属性类型。

我想我必须实现一个表和行类才能正常工作。我感到困惑的是存储具有不同列值属性类型的表的数据结构，以及所述表和行类的布局究竟是什么样子的。

任何帮助将不胜感激！

Answer 1

好的，我建议你使用 https://github.com/vincentlaucsb/csv-parser

对于您的情况，您只应该删除带有类型的行，因为 C++ 无法动态生成类(所有类型都应该在编译时已知(

这是您的案例的示例

#include <iostream>
#include <string>
#include "csv-parser/single_include/csv.hpp"
using namespace csv;
bool string_to_bool(std::string state)
{
if (state == "FALSE")
return false;
if (state == "TRUE")
return true;
throw std::runtime_error("incorrect input");
}
struct Data
{
int year;
std::string category;
bool winner;
std::string entity;
};
int main()
{
CSVReader reader("...enter path to your file ... /data.csv");
std::vector<Data> entities;
for (auto& row : reader)
{
Data entity;
entity.year = row["year"].get<int>();
entity.winner = string_to_bool(row["winner"].get<std::string>());
entity.category = row["category"].get<std::string>();
entity.entity = row["entity"].get<std::string>();
entities.push_back(entity);
}
}

CSV 文件

year,category,winner,entity
2015,CHEF OF THE YEAR,FALSE,John Doe
2015,CHEF OF THE YEAR,FALSE,Bob Brown
2015,CHEF OF THE YEAR,TRUE, William Thorton
2015,CHEF OF THE YEAR,FALSE,Jacob Smith

创建 CMakeLists.txt

对于安装解析器，只需执行

git clone https://github.com/vincentlaucsb/csv-parser.git 

并添加 CMakeLists.txt

cmake_minimum_required(VERSION 3.15)
project(project_name)
set(CMAKE_CXX_STANDARD 17)
add_subdirectory(csv-parser)
add_executable(project_name main.cpp)
target_link_libraries(project_name csv)

项目层次结构

$ ll       
total 24
-rw-r--r--@  1 user  staff   192B Jan 26 12:14 CMakeLists.txt
drwxr-xr-x@  9 user  staff   288B Jan 26 12:14 cmake-build-debug
drwxr-xr-x  23 user  staff   736B Jan 26 11:18 csv-parser
-rw-r--r--   1 user  staff   191B Jan 26 11:54 data.csv
-rw-r--r--@  1 user  staff   871B Jan 26 12:02 main.cpp

Answer 2

您在评论中询问了不使用库的解决方案。您要求更多(变体数据类型(，但我首先展示了一种标准的C++方法。

我想，你已经完成了你的任务。如果您仍然感兴趣，我会给您更详细的解释。

#include <iostream>
#include <sstream>
#include <vector>
#include <regex>
#include <string>
#include <iterator>
#include <algorithm>
// the delimiter for the csv
const std::regex re(",");
// One DataRow from the csv file
struct DataRow {
int year{};
std::string category{};
bool winner{};
std::string entity{};
friend std::istream& operator >> (std::istream& is, DataRow& dr) {
// Read one complete line
if (std::string line{}; std::getline(is, line)) {
// Split the string, containing the complete line into parts
std::vector<std::string> part(std::sregex_token_iterator(line.begin(), line.end(), re, -1), {});
// Convert into our local data / types
if (4U == part.size()) {
dr.year = std::stoi(part[0]);
dr.category = part[1];
dr.winner = (part[2] == "TRUE") ? true : false;
dr.entity = part[3];
}
}
return is;
}
// Simple data output
friend std::ostream& operator << (std::ostream& os, const DataRow& dr) {
return os << "nYear:     " << dr.year << "nCategory: " << dr.category << "nWinner:   " << dr.winner << "nEntity:   " << dr.entity << "n";
}
};
// This will hold all CSV data
struct CSV{
std::vector<std::string> header{};
std::vector<std::string> types{};
std::vector<DataRow> data{};
// Extractor
friend std::istream& operator >> (std::istream& is, CSV& c) {
if (std::string line{}; std::getline(is, line)) {
// Read and parse header
c.header.clear();
std::copy(std::sregex_token_iterator(line.begin(), line.end(), re, -1), {}, std::back_inserter(c.header));
if (std::getline(is, line)) {
// Read and parse types
c.types.clear();
std::copy(std::sregex_token_iterator(line.begin(), line.end(), re, -1), {}, std::back_inserter(c.types));
// Get all data. Read all lines and parse them
c.data.clear();
std::copy(std::istream_iterator<DataRow>(is), {}, std::back_inserter(c.data));
}
}
return is;
}
// Make some nice output
friend std::ostream& operator << (std::ostream& os, const CSV& c) {
os << "Header: ";
std::copy(c.header.begin(), c.header.end(), std::ostream_iterator<std::string>(os, "  "));
os << "nTypes:  ";
std::copy(c.types.begin(), c.types.end(), std::ostream_iterator<std::string>(os, "  "));
os << "nnData:n";
std::copy(c.data.begin(), c.data.end(), std::ostream_iterator<DataRow>(os, "  "));
return os;
}
};
std::istringstream csvFile{ R"(year,category,winner,entity
INT,STRING,BOOL,STRING
2015,CHEF OF THE YEAR,FALSE,John Doe
2015,CHEF OF THE YEAR,FALSE,Bob Brown
2015,CHEF OF THE YEAR,TRUE,William Thorton
2015,CHEF OF THE YEAR,FALSE,Jacob Smith)" };

int main() {
// Define a variable of type CSV. This will hold all data
CSV csv{};
// Read from a file and put everything into our variable
csvFile >> csv;
// Show all contents of CSV on screen
std::cout << csv;
return 0;
}````