Reroute stdout to string

Question

OK, so here's what I'm trying to do :

A portion of my program outputs text to console
For unittest purposes, I'd like to be able to get that output into a string, so that I can use it in an assert check.

How is that possible?

NOTE:

Guys, sorry if I mislead you. I'm looking for a solution in D.

You could create a custom output function that concatenates to a string and then outputs data. Like a custom printf or a custom istream if you prefer C++ — Kelm, Apr 24 '14 at 12:50
perhaps you need [freopen](http://www.cplusplus.com/reference/cstdio/freopen/). — Dayal rai, Apr 24 '14 at 12:51
@al-Acme Close... OSX. lol. However, I'm not looking for a platform-specific solution. — Dr.Kameleon, Apr 24 '14 at 12:51
possible duplicate of [redirect output from stdout to a string?](http://stackoverflow.com/questions/14428406/redirect-output-from-stdout-to-a-string) — Sadique, Apr 24 '14 at 12:52
The easiest way to do something like this in standard C is to use `fprintf(stream, ...)` where "stream" is stdout in the normal case and a text file in the test case. — Lundin, Apr 24 '14 at 12:52
@alAcme and Lundin, this is a D Programming Language question. — Vladimir Panteleev, Apr 24 '14 at 13:14

Vladimir Panteleev · Accepted Answer · 2014-04-25T10:01:09.863

Here is a way to do this using pipes and threads (which, unlike the suggested duplicate, is not limited to a predefined buffer size or risks a buffer overflow vulnerabillity):

Create a pipe using std.process.pipe
Set stdout to the pipe's write end (back it up first)
Spawn a thread which would read from the pipe's read end and append output to a string, until the pipe is closed
Execute the task at hand
Close the write end of the pipe
Restore the old value of stdout
Wait for the thread to finish execution
Use the buffer created by the thread

I have some similar code, albeit in the other direction (asynchronous writing as opposed to reading), here and here.

score 0 · Answer 2 · answered Apr 24 '14 at 13:54

Well, I just think I've found a working way myself :

import std.stdio;
import std.conv;
import std.file;

//

string getOutput()
{
     auto initialStdout = stdout;

     // Redirect output to file
     string tmpfile = "tmp/test.out";
     stdout.open(tmpfile, "wt");

     //
     // Do whatever you want to,
     // that generates some output
     //

     stdout = initialStdout; // Restore stdout to what it was

     return to!string(std.file.read(tmpfile)); // Return output
}

score 0 · Answer 3 · answered Apr 24 '14 at 16:25

0

Simply use std.process.executeShell . The example from the Phobos documentation is good enough for you to do what you need.

answered Apr 24 '14 at 16:25

DejanLekic

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Reroute stdout to string

3 Answers3