ifstream read every files that start with

Question

I have multiple files that start with employee_

Examples : 
  employee_2053.txt
  employee_1284.txt
  employee_4302.txt
  etc...

What I want is to read the content of every file. I tried something like this:

string fname, lname;

ifstream file("employee_" + *);
while(file>>fname>>lname) {
    // Do something here that is gonna be repeated for every file
}

I have an error at "employee_" + *. When I think about it, it makes sense that it doesn't work. I guess I will need a loop or something, I just don't know how to do it.

You need to iterate through the directory and get all the filenames first. Then, you'll need to see which ones of those start with 'employee' and open them. The code for iterating through a directory will depend on which platform you are on. — Anmol Singh Jaggi, Jan 26 '18 at 17:41
boost::filesystem may help if you compiler does not support std::filesystem. — drescherjm, Jan 26 '18 at 17:51

Ron · Accepted Answer · 2018-01-26T18:09:52.890

3

Enumerate the available files using the OS specific API and store the names inside a container such as vector of strings std::vector<std::string> v;. Iterate over a container:

for (auto el : v) {
    std::ifstream file(el);
    // the code
}

If you know for sure there are existing files with range based hard coded values you can utilize the std::to_string function inside a for loop:

for (size_t i = 0; i < 4000; i++) {
    std::ifstream file("employee_" + std::to_string(i) + ".txt");
    // the code
}

Update:
As pointed out in the comments the alternative to OS API is a file system support in the C++17 standard and the Boost Filesystem Library.

edited Jan 26 '18 at 18:09

answered Jan 26 '18 at 17:42

Ron

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C++ 17 introduces a [cross-platform filesystem API](http://en.cppreference.com/w/cpp/filesystem), so OP might be able to avoid the OS specific API. – hnefatl Jan 26 '18 at 17:54
1

I think the first solution is the best if you have some "holes" in the employee numbers, because it will avoid a lot of attempts to open not existing files. The second is the best if the numbers are contiguous. – Benjamin Barrois Jan 26 '18 at 17:56
The simplest way is with the `for (size_t i = 0; i < 4000; i++)` loop – Charles-François St-Cyr Jan 26 '18 at 17:56

ifstream read every files that start with

1 Answers1