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could anyone provide a small example or direct me to proper reading material in order to solve the following problem:

    ls | ./myprog

What I would like to achieve is that my program reads information from ls and just print it on the screen.

I need c++ example, and if possible to do this through boost lib

thnx

P.S.

Thank you all it worked

user8060
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  • Shouldn't need anything particularly special - just regular `while(std::cin >> myvariable) { ... }` or similar should work. The beauty of the "generic input system" is that pipes, redirected files and consoles work the same way. – Mats Petersson Mar 08 '15 at 16:38
  • The "pipe" is not part of your program but rather how the environment for running your program is set up by the shell. – Ulrich Eckhardt Mar 08 '15 at 16:52

2 Answers2

0

In C, all you need to do is read the file descriptor 0:

read(0, …, …);

In C++, you can do this by using std::cin:

#include <iostream>
int main() {
    std::cin >> /* a variable you want to direct the input to */
    return 0;
}

That's standard C++ that is fully compatible with boost. For the way to use it, I leave it to you to read more on the manual and the plethora of examples you can find online.

for opening a file or reading from stdin you can do something in the following fashion:

shared_ptr<istream> input;
if (filename == "-" || filename == "")
    input.reset(&cin, [](...){});
else
    input.reset(new ifstream(filename.c_str()));

// ...

(answer copied from https://stackoverflow.com/a/2159469/1290438)

Basically, if you don't give a filename parameter, you consider data comes from stdin. That's the way cat works.

Community
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zmo
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  • thnx ! what would then be a solution if sometimes i want to read from file and sometimes from stdin. let say I only have one loop and I need to read input character one at a time (get()) i cannot use cin then. Right? – user8060 Mar 08 '15 at 17:33
  • Of course you read one character at a time, just you the [`read()` method](http://www.cplusplus.com/istream::read) of `istream` which is the class of `cin`, to which you can give the number of character to read. But do you really want to that? If you're reading a file as input, you might prefer to read it line by line. – zmo Mar 08 '15 at 21:55
0

this code matches exactly your Problem:

#include <iostream>

using namespace std;

    int main()
{ 
while (true)
    {
        string x;
        cin >> x;
        cout << x << endl;
    }
}

you have to put this code into your "myprog" cpp file and then type the command you've mentioned. It simply puts the input from the ls program to your screen

Daniel Jäckel
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