Tuesday coding tips are super short posts about various tidbits mainly from C++, but also from other programming languages I use. You can also follow the #TuesdayCodingTips hashtag on Mastodon and Linkedin.
Resource Acquisition is Initialization (RAII) is an awfully named principle saying that your class should be fully usable after construction and should clean itself up in the destructor (in other words, no (de)init methods). This principle is common in modern programming languages and is also adopted in modern C++ codebases.
But what if you work with C-like API like fopen? It returns a pointer you need to manually free before it goes out of scope. Otherwise, you leak memory and open file handles. This is where smart pointers come to the rescue as you can wrap raw pointers with them and give them custom callbacks to execute when they leave the scope.
#include <cstdlib>
#include <iostream>
#include <memory>
// MSVC disallows calling fopen
#pragma warning(disable : 4996)
void CloseFile(FILE* f)
{
std::cout << "Closing file" << std::endl;
fclose(f);
}
auto SafeFopen(const char* path, const char* mode)
{
return std::unique_ptr<FILE, decltype(&CloseFile)>(
fopen(path, mode), CloseFile);
}
int main()
{
auto&& fp = SafeFopen("myfile.txt", "w");
return 0;
// Outputs: Closing file
}