PHP与CSV

PHP、Java 与 C++ 在处理 CSV 文件中的应用对比

CSV(Comma-Separated Values,逗号分隔值)是一种简单的文件格式，用于存储表格数据，在处理大量数据时，CSV 文件是一种非常实用的数据存储方式，本文将对比 PHP、Java 和 C++ 这三种编程语言在处理 CSV 文件时的特点和优势。

我们来看 PHP，PHP 是一种流行的服务器端脚本语言，广泛应用于 Web 开发，在处理 CSV 文件时，PHP 可以使用内置的fgetcsv() 函数来读取和解析 CSV 文件。fgetcsv() 函数接受一个文件指针和一个整数作为参数，返回一个包含 CSV 数据的二维数组，PHP 还提供了诸如fputcsv()、fgetcsv() 等函数，方便用户对 CSV 数据进行写入、读取和操作。

<?php
// 从 CSV 文件中读取数据
$file = fopen('example.csv', 'r');
while (($data = fgetcsv($file)) !== false) {
    print_r($data);
}
fclose($file);
?>

接下来是 Java，Java 是一种面向对象的编程语言，具有跨平台的优势，在处理 CSV 文件时，Java 可以借助 Apache Commons CSV 这个开源库来实现，Apache Commons CSV 提供了丰富的 API,支持读取、写入和操作 CSV 数据，使用 Apache Commons CSV,用户可以轻松地将 CSV 数据转换为 Java 对象或从 Java 对象转换为 CSV 数据。

import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;
import java.io.FileReader;
import java.io.IOException;
import java.util.List;
public class CSVReaderExample {
    public static void main(String[] args) throws IOException {
        FileReader fileReader = new FileReader("example.csv");
        CSVParser csvParser = new CSVParser(fileReader, CSVFormat.DEFAULT);
        for (CSVRecord record : csvParser) {
            System.out.println(record);
        }
        csvParser.close();
    }
}

C++，C++ 是一门系统级编程语言，性能优越，在处理 CSV 文件时，C++ 可以借助第三方库如 RapidJSON 或者 libcsv 实现，这些库提供了简洁的 API,方便用户对 CSV 数据进行读取、写入和操作，libcsv 支持将 CSV 数据转换为 std::vector<std::vector<std::string>> 或者从 std::vector<std::vector<std::string>> 转换为 CSV 数据。

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
#include <string>
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include "libcsv/csv.h"
#include "libcsv/exceptions.h"
#include "libcsv/resultsetreader.h"
using namespace rapidjson;
using namespace libcsv;
using namespace std;
int main() {
    ResultSet resultSet = readFile("example.csv", ',');
    int rowCount = resultSet.getRowCount();
    int colCount = resultSet.getColumnCount();
    ostringstream oss;
    oss << fixed << setprecision(2); // Set precision to two decimal places for floating-point values in the output JSON string.
    ostream_wrapper jsonWriter(oss); // Wrap ostream with ostream_wrapper to use it as a JSON writer.
    Document document; // Create a JSON document object to store the parsed data.
    Value root(kObjectType); // Create a top-level object in the JSON document.
    int index = 0; // Index variable to keep track of the current column being written to the JSON object.
    ResultSetIterator resultSetIterator = resultSet.createResultSetIterator(); // Create an iterator to iterate through the rows in the result set.
    while (resultSetIterator->next()) { // Iterate through each row in the result set.
        Value obj(kObjectType); // Create a JSON object to store the current row's data in the JSON document.
        for (int i = 0; i < colCount; i++) { // Iterate through each column in the row.
            if (index >= colCount) break; // Exit the loop if we've reached the end of the row and need to start writing to the next row in the JSON object.
            string cellValue = resultSetIterator->getString(i); // Get the value of the current cell in the row as a string.
            obj[to_string(index)] = move(cellValue); // Add the value of the current cell to the JSON object at the current column index.
            index++; // Move on to the next column in the row.
        }
        root.AddMember(move(to_string(index)), move(obj), kObjectType); // Add the JSON object representing the current row to the top-level object in the JSON document.
    }
    document.Accept(jsonWriter); // Use the ostream_wrapper as a JSON writer to write the parsed data to a string buffer. The string buffer will contain the JSON string containing the parsed data from the CSV file.
    ostringstream jsonStringBuffer; // Create an ostringstream object to hold the contents of the string buffer containing the JSON string containing the parsed data from the CSV file. Convert it to a string using its str() method. This is equivalent to calling toString() on the string buffer object itself, but it can be more efficient and avoid potential memory leaks when working with large strings or long-lived objects that need to manage their own resources carefully. const char* jsonString = jsonStringBuffer.str().c_str(); // Convert the string contained in the ostringstream object to a C-style null-terminated char array by calling its c_str() method and passing it to a const char* pointer variable named jsonString. Now you can use this pointer variable to pass its value to any function that expects a C-style null-terminated char array as input, such as printf() or fprintf(). return jsonString; // Return the JSON string containing the parsed data from the CSV file as a function result or output parameter, depending on your program's design and requirements.