This is a text-only version of the following page on https://raymii.org: --- Title : C++ create and write to a CSV file with a variadic template Author : Remy van Elst Date : 17-06-2019 URL : https://raymii.org/s/snippets/Cpp_create_and_write_to_a_CSV_file_with_a_variadic_template.html Format : Markdown/HTML --- In this snippet I'll show you a [variadic template][1] to write to a file. In line with my [other experiments][3] to get a better grasp at templates, this example improves on my [earlier attempt][2] by using a variadic template, thus allowing you to provide an infinite number of columns to the csv file of any type that has the overloaded `<<` operator.

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In [the first example][2] I wrote to a CSV file with a set amount of columns and types. After experimenting some more with templates and variadic templates, I tried to create this function again but with templates. A simple example, without any checking if a file already exists or is successfully opened. It would probably be better to pass the CSV data via a `struct` since most of the time the data format is going to be the same. ### The code #include #include #include std::mutex logMutex; bool fileExists(std::string& fileName) { return static_cast(std::ifstream(fileName)); } template void writeFile(filename &fileName, Arg arg) { std::lock_guard csvLock(logMutex); std::fstream file; file.open (fileName, std::ios::out | std::ios::app); if (file) file << arg; } template void writeFile(filename &fileName, First first, Args... args) { writeFile(fileName, first); writeFile(fileName, args...); } int main() { std::string theFile = "a"; if(!fileExists(theFile)) writeFile(theFile, "\"header1\",", "\"header2\",", "\"header3\"", "\n"); writeFile(theFile, "\"data1\",", "\"data2\",", "\"data3\"", "\n"); writeFile(theFile, "\"second1\",", "\"second2\",", "\"second3\"", "\n"); return 0; } [1]: https://raymii.org/s/snippets/Cpp_variadic_template_recursive_example.html [2]: https://raymii.org/s/snippets/Cpp_create_and_write_to_a_csv_file.html [3]: https://raymii.org/s/blog/Cooking_with_Cpp_templates_and_stronger_types.html --- License: All the text on this website is free as in freedom unless stated otherwise. This means you can use it in any way you want, you can copy it, change it the way you like and republish it, as long as you release the (modified) content under the same license to give others the same freedoms you've got and place my name and a link to this site with the article as source. This site uses Google Analytics for statistics and Google Adwords for advertisements. You are tracked and Google knows everything about you. Use an adblocker like ublock-origin if you don't want it. All the code on this website is licensed under the GNU GPL v3 license unless already licensed under a license which does not allows this form of licensing or if another license is stated on that page / in that software: This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . Just to be clear, the information on this website is for meant for educational purposes and you use it at your own risk. I do not take responsibility if you screw something up. Use common sense, do not 'rm -rf /' as root for example. If you have any questions then do not hesitate to contact me. See https://raymii.org/s/static/About.html for details.