How can I test if either of two files exist? - c++

Question

I am new to C++,
I am using a while true to find a Pass.txt file.
Once it finds it the while loop breaks and prints "Pass.txt file FOUND"
This works fine
I then would like to see if it can find Pass.txt OR Fail.txt with a while true
something like this ifstream ifile("Pass.txt || Fail.txt");
This does not work:
cout << " ------------------------------------------\n";
cout << " Searching for Pass or Fail file \n";
cout << " ------------------------------------------\n";
cout << "\n\n";
while (true)
{
ifstream ifile("Pass.txt");
//ifstream ifile("Pass.txt ||Fail.txt");
if (ifile)
{
// The file exists, and is open for input
break;
}
}
cout << "\n\n";
cout << " ------------------------------------------\n";
cout << " Pass.txt FOUND \n";
cout << " ------------------------------------------\n";
cout << " ------------------------------------------\n";

Answer 1

Your code fails because you’re not testing for the existence of two files. You are testing whether the one file with the weird name Pass.txt || Fail.txt exists. You need two make two separate existence checks, one for each separate file.
To do this, don’t open the file — use std::filesystem::exists:
#include <filesystem>
#include <thread>
// …
int main() {
using namespace std::chrono_literals;
namespace fs = std::filesystem;
while (not fs::exists("Pass.txt")) {
std::this_thread::sleep_for(500ms); // Be gentle to the system.
}
while (not (fs::exists("Pass.txt") or fs::exists("Fail.txt"))) {
std::this_thread::sleep_for(500ms); // Be gentle to the system.
}
}
(You can also write ! instead of not, and || instead of or; but I prefer using these descriptive terms in my own code.)
We use std::this_thread::sleep to avoid hammering the system with a busy loop, which will spin up your CPU like crazy even though your code isn’t doing any real work.
However, note that merely testing for a file’s existence isn’t very useful. And your second loop will immediately terminate, since "Pass.txt" exists after the first loop (unless, by a freak coincidence, it was deleted in the nanoseconds between the two loops).