RAII (Resource Acquisition is Initialization)

• std::lock_guard
• std::unique_ptr
• std::shared_ptr
• std::unique_lock
• std::jthread
• std::fstream

#include <iostream>
#include <memory>
 
// // before C++ 20
// struct file_closer {
//     void operator()(FILE* stream) {fclose(stream);}
// };
// using cfile = std::unique_ptr<FILE, file_closer>;
 
// C++ 20
using cfile = std::unique_ptr<FILE, decltype([](FILE* stream){fclose(stream);})>;
 
auto make_cfile(char const* file_name, char const* mode) {
    FILE* stream{fopen(file_name, mode)};
    if(not stream) {
        throw std::runtime_error{"Failed to open file"};
    }
    return cfile{stream};
}
 
void fn() {
    auto file{make_cfile("file_name.txt", "w")};
    fprintf(file.get(), "data for the file");
}
 
int main() {
    fn();
    return 0;
}

Reference

• Back to Basics: RAII in C++ - Andre Kostur - CppCon 2022
• Back to Basics: RAII and the Rule of Zero - Arthur O’Dwyer - CppCon 2019