Thread: Determine if input is file or directory

Hi:

How can I determine whether an input string refers to a file or a directory?

For example: input is /internet/test

Is this a file or a directory? Is there a way to determine this using C++?

Thanks.

Check the string for slashes or backslashes.

Code:

std::string input;
/* User Entry */
if(input.find("/") == std::string::npos && input.find("\\") == std::string::npos) /* File is in the current directory */
else /* File is in another directory */

You can use one of the stat() function on it and find out the type that way. For more info: http://www.die.net/doc/linux/man/man2/stat.2.html

Originally Posted by SlyMaelstrom

Check the string for slashes or backslashes.

I'm sorry, but I don't quite understand. In Unix, the "test" could be a file or a directory. Assuming this is user-inputted, how can I (or the program) determine?

Thanks.

Ah I understand, I wasn't thinking clearly. Try itsme's suggestion.

v Same goes to you down there v

>Check the string for slashes or backslashes.
How does that work? Let's say I have "/mydir/something", how do you know what "something" is when it could be either a directory or a file and the string contains slashes? There's no way to determine such a thing in every case based solely on the contents of the path.

Originally Posted by itsme86

You can use one of the stat() function on it and find out the type that way. For more info: http://www.die.net/doc/linux/man/man2/stat.2.html

Thanks for the suggestion. Is there a way to do this on Windows as well? I understand that most Windows files will have an extension, but in a mixed environment, there really can't be a guarantee .

Originally Posted by SlyMaelstrom

Ah I understand, I wasn't thinking clearly. Try itsme's suggestion.

v Same goes to you down there v

Thanks anyway, bud .

I've used stat() in Windows with several different compilers. I know it works for sure with Dev-C++:

Code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>

int main(void)
{
  struct stat st;

  if(stat("C:\\", &st) == -1)
    puts("Error!");
  else
    printf("C:\\ is%s a directory!\n", S_ISDIR(st.st_mode) ? "" : " not");

  if(stat("C:\\io.sys", &st) == -1)
    puts("Error!");
  else
    printf("C:\\io.sys is%s a directory!\n", S_ISDIR(st.st_mode) ? "" : " not");

  return 0;
}

My output:

C:\ is a directory!
C:\io.sys is not a directory!

Oops, sorry. Forgot this was the C++ side of things. Maybe someone can C++ify it for you.

Originally Posted by itsme86

Oops, sorry. Forgot this was the C++ side of things. Maybe someone can C++ify it for you.

Nah, it's cool. I'm glad to learn anyway .

Code:

#include <fstream>

ofstream fout;
fout.open("/internet/test", ios::out);

I don't think ofstream creates files that don't exist, so it should be okay.

If test is a directory this function will fail, so it's merely important to check the state of the stream after you open it. Most operating systems can handle files without extentions these days, so it's possible that it will work if "test" exists as a datafile.

Thanks all. The stats thing worked with Borland 5.5 .

as Daved said
>> Boost has a file system library that might also help with this if stat isn't enough.

Code:

#include "boost/filesystem/operations.hpp" // includes boost/filesystem/path.hpp
#include "boost/filesystem/fstream.hpp"    // ditto
#include <iostream>                        // for std::cout
using boost::filesystem;                   // for ease of tutorial presentation;

path my_path( "/internet/test" );
if (is_directory(my_path))
{
    std::cout << "it's a directory!" << std::endl;
}

what could be simpler?

edit: oh and it's portable too!