How can you open a file that the user specifies on the command line?

Question

Suppose you want to allow the user to specify a file to open on the command line. How can this be achieved if the user will enter data such as:

/User/desktop/input.txt

How can I then convert this directory into something that the program actually opens/reads?

Y do you need the file name alone? The whole path is needed to open that particular file.. — Aswin Murugesh, Dec 05 '13 at 08:28
Why would you need to split the path ? If you use just the filename and not the path how will you guarantee you know the directory ? — Johan, Dec 05 '13 at 08:28
It's kind of unclear what do you mean by 'specifies on the command line'. Did you just mentioned command line, because you're building a console application or do you want to pass the filename/path on command-line to your program? — Constantin, Dec 05 '13 at 08:43

score 1 · Answer 1 · edited May 23 '17 at 11:56

The parameter argc holds the count of command line arguments. If you don't pass any arguments, it's 1 (argv[0] is just the name of your executable). Otherwise its the count of command line arguments + 1.

#include <fstream>

int main (int argc, char **argv){
  if(argc>1){
    std::ifstream a(argv[1]); // first argument
    if(a){
      //file opened
    }
  }
}

To start this program, you would type on your command-line:

nameOfYourExecutable.exe /User/desktop/input.txt

See also here for further informations.

score 1 · Answer 2 · answered Dec 05 '13 at 08:34

1

std::ifstream is the way.

std::ifstream file(your_file_path);

if (!file) { return; } // check the file 

std::string line;
while (getline(file, line)) { /* do some process on line */ }

answered Dec 05 '13 at 08:34

Johan

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score 0 · Answer 3 · answered Dec 05 '13 at 08:31

0

Just open("path",permissions,flags) will work fine.. and you can read or write using the file descriptor.

answered Dec 05 '13 at 08:31

Aswin Murugesh

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@user3064097: as simple as it is – Aswin Murugesh Dec 05 '13 at 08:33

score 0 · Answer 4 · answered Dec 05 '13 at 08:32

0

What is the deference if you get it from the command line argument, or hard-code it in your program? just use open().

answered Dec 05 '13 at 08:32

yosim

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How can you open a file that the user specifies on the command line?

4 Answers4