I started to learn C++ after programming for some years in Java, and this is my first (header-only) library. When switching from another language, it is always difficult not to project the old habits into the new medium, and thus I wonder how idiomatic my C++ code is, so it would be awesome if someone reviewed this piece.
#ifndef __FILE_READER_H__#define __FILE_READER_H__#include <filesystem>#include <fstream>#include <functional>#include <stdexcept>#include <string>#include <vector>// APInamespace octarine { // Read a CSV file into a vector of vectors of strings. // Each string is trimmed of whitespace. inline std::vector<std::vector<std::string>> read_csv( const std::filesystem::path &filename, bool has_header = true, char separator = ','); // Read a CSV file into a vector of objects of a predefined type. template <typename T> inline std::vector<T> read_csv( const std::filesystem::path &filename, const std::function<T(const std::vector<std::string>&)>& mapper, bool has_header = true, char separator = ',' );}// Implementationnamespace octarine { namespace { size_t count_items(const std::string& line, char separator); std::vector<std::string> parse_line(const std::string &line, char separator, size_t num_items, size_t line_number); const char* k_whitespace = " \t"; } template <typename T> std::vector<T> read_csv( const std::filesystem::path &filename, const std::function<T(const std::vector<std::string>&)>& mapper, bool has_header, char separator) { const auto& lines = read_csv(filename, has_header, separator); std::vector<T> result; result.reserve(lines.size()); for (const auto& line : lines) { result.emplace_back(mapper(line)); } return result; } std::vector<std::vector<std::string>> read_csv( const std::filesystem::path &filename, bool has_header, char separator) { std::ifstream f(filename); if (!f.good()) { throw std::invalid_argument("unable to read file '"+ filename.string() +"'"); } // read header line std::string header; std::getline(f, header); if (!f.good()) { throw std::invalid_argument("error reading header line from '"+ filename.string() +"'"); } // count number of items per line size_t num_items = count_items(header, separator); // if we don't have the header, add the first line to the results std::vector<std::vector<std::string>> lines; size_t line_number = 1; if (!has_header) { lines.push_back(parse_line(header, separator, num_items, line_number)); line_number += 1; } std::string line; while (!f.bad()) { std::getline(f, line); if (f.eof()) { break; } if (f.fail()) { throw std::invalid_argument("error reading line from '"+ filename.string() +"'"); } lines.push_back(parse_line(line, separator, num_items, line_number)); line_number += 1; } return lines; } namespace { // counts number of comma-separated items in a line from a CSV file size_t count_items(const std::string &line, char separator) { size_t count = 1; for (char c : line) { if (c == separator) {++count; } } return count; } // splits a line from a CSV file when the number of items per line is known in advance std::vector<std::string> parse_line( const std::string &line, char separator, size_t num_items, size_t line_number) { if (num_items == 0) { throw std::invalid_argument("number of items must be positive"); } std::vector<std::string> result(num_items); size_t item = 0; size_t offset = 0, end_offset = 0; size_t max_offset = line.size(); size_t index; while (end_offset != max_offset) { if (item >= num_items) { throw std::length_error("line "+ std::to_string(line_number) +": found more items in a line than expected"); } index = line.find(separator, offset); end_offset = (index != std::string::npos) ? index : max_offset; size_t non_space_start = line.find_first_not_of(k_whitespace, offset); size_t non_space_end = line.find_last_not_of(k_whitespace, end_offset - 1); if (non_space_start == std::string::npos || non_space_end == std::string::npos || non_space_start == index) { result[item] = ""; } else { result[item] = line.substr(non_space_start, non_space_end - non_space_start + 1); } offset = end_offset + 1; item += 1; } return result; } }}#endif
