Working with CSV in C++: Libraries, Parsing, and Data Writing

Working with CSV in C++: Libraries and Practical Examples

CSV (Comma-Separated Values) is one of the most common formats for storing tabular data. C++ does not have built-in CSV support in the standard library (until C++23), so developers use third-party libraries or write their own parsers. In this article, we will cover the main approaches to working with CSV in C++: from manual parsing to ready-made solutions.

Why are CSV libraries needed?

CSV files seem simple, but in practice they contain many pitfalls:

• Escaping quotes inside fields (e.g., "Hello, world")
• Multiline values
• Different delimiters (comma, semicolon, tab)
• Different encodings (UTF-8, UTF-16, ANSI)

Ready-made libraries solve these problems and save time.

1. Manual CSV Parsing (without third-party libraries)

For simple cases, you can write a parser yourself. Example of reading CSV using std::ifstream and std::getline:

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

std::vector<std::vector<std::string>> parseCSV(const std::string& filename) {    std::vector<std::vector<std::string>> data;    std::ifstream file(filename);    std::string line;

    while (std::getline(file, line)) {        std::vector<std::string> row;        std::stringstream ss(line);        std::string cell;

        while (std::getline(ss, cell, ',')) {            // Remove extra quotes (simplified)            if (cell.size() >= 2 && cell.front() == '"' && cell.back() == '"') {                cell = cell.substr(1, cell.size() - 2);            }            row.push_back(cell);        }        data.push_back(row);    }    return data;}

Disadvantages: does not handle escaped commas inside quotes, multiline fields, or empty lines at the end of the file.

2. The libcsv Library (C)

libcsv is a lightweight C library that correctly parses CSV according to RFC 4180. Suitable for projects where performance is important.

Installation (Linux): sudo apt-get install libcsv-dev

#include <csv.h>#include <iostream>#include <vector>

void cb1(void *s, size_t len, void *data) {    std::string field(static_cast<char*>(s), len);    static_cast<std::vector<std::string>*>(data)->push_back(field);}

void cb2(int c, void *data) {    if (c == CsvRowEnd) {        // End of row — output        auto& row = *static_cast<std::vector<std::string>*>(data);        for (const auto& f : row) std::cout << f << " | ";        std::cout << "";        row.clear();    }}

int main() {    FILE *fp = fopen("data.csv", "r");    if (!fp) return 1;

    struct csv_parser p;    csv_init(&p, CSV_STRICT);

    std::vector<std::string> row;    char buf[1024];    size_t bytes_read;

    while ((bytes_read = fread(buf, 1, sizeof(buf), fp)) > 0) {        csv_parse(&p, buf, bytes_read, cb1, cb2, &row);    }    csv_fini(&p, cb1, cb2, &row);    csv_free(&p);    fclose(fp);    return 0;}

3. The rapidcsv Library (C++ header-only)

rapidcsv is a modern C++17 library that works with header files only. It supports automatic delimiter detection, working with different data types, and CSV writing.

Installation: copy rapidcsv.h into the project.

#include "rapidcsv.h"#include <iostream>#include <vector>

int main() {    // Reading CSV    rapidcsv::Docum