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digitalmars.D.learn - stdin/stdout and flush

reply Andre Pany <andre s-e-a-p.de> writes:
Hi,

I have a small application like this:

---a.d
import std;

void main()
{
     while(true)
     {
         string enemy1 = readln.strip;
         int dist1 = to!int(readln.strip);
         string enemy2 = readln.strip;
         int dist2 = to!int(readln.strip);
         writeln((dist1 < dist2) ? enemy1 : enemy2);
         stdout.flush();
     }
}
---


This applications will be called by a second application:

---b.d
import std;

void main()
{
     auto p = pipeShell("a", Redirect.all);
     p.stdin.writeln("e1");
     p.stdin.writeln("10");
     p.stdin.writeln("e2");
     p.stdin.writeln("9");

     p.stdin.flush();
     p.stdout.readln();

     import core.thread: Thread;
     import core.time: seconds;

     Thread.sleep(3.seconds);
}
---

I compile a.d using command ```dmd a.d``` and run b.d using 
command ```dmd -run b.d```

In application a.d the first "while round" will succeed as 
expected. But in the second "while round" the readln does not 
wait until there is an input but gets an empty string. The to!int 
will therefore throw an exception.

Why does the readln returns an empty string in the second run and 
does not wait on an input?

Kind regards
André
Aug 27 2019
parent reply a11e99z <black80 bk.ru> writes:
On Tuesday, 27 August 2019 at 20:09:34 UTC, Andre Pany wrote:

 
 This applications will be called by a second application:
 import std;
 void main() {
     auto p = pipeShell("a", Redirect.all);
     p.stdin.writeln("e1");
     p.stdin.writeln("10");
     p.stdin.writeln("e2");
     p.stdin.writeln("9");
     p.stdin.flush();
     p.stdout.readln();
 }

 In application a.d the first "while round" will succeed as 
 expected. But in the second "while round" the readln does not 
 wait until there is an input but gets an empty string. The 
 to!int will therefore throw an exception.

 Why does the readln returns an empty string in the second run 
 and does not wait on an input?


probably cuz no second "send round" in b.d.
or u mean second half-round "e2,9"?
Aug 27 2019
parent reply Andre Pany <andre s-e-a-p.de> writes:
On Tuesday, 27 August 2019 at 20:45:44 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 20:09:34 UTC, Andre Pany wrote:

 
 This applications will be called by a second application:
 import std;
 void main() {
     auto p = pipeShell("a", Redirect.all);
     p.stdin.writeln("e1");
     p.stdin.writeln("10");
     p.stdin.writeln("e2");
     p.stdin.writeln("9");
     p.stdin.flush();
     p.stdout.readln();
 }

 In application a.d the first "while round" will succeed as 
 expected. But in the second "while round" the readln does not 
 wait until there is an input but gets an empty string. The 
 to!int will therefore throw an exception.

 Why does the readln returns an empty string in the second run 
 and does not wait on an input?


 probably cuz no second "send round" in b.d.
 or u mean second half-round "e2,9"?


I mean the coding in the while loop is executed twice.

If I start application A in the console using ```dmd -run a.d``` 
the readln functions are waiting on stdin input in first and 
second execution of the while logic.

But if application A is called from application B then in the 
second execution of the while loop, the readln statements just 
return empty strings.

Do I have to clear some buffers?

Kind regards
Andre
Aug 27 2019
next sibling parent reply a11e99z <black80 bk.ru> writes:
On Tuesday, 27 August 2019 at 21:01:58 UTC, Andre Pany wrote:

 On Tuesday, 27 August 2019 at 20:45:44 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 20:09:34 UTC, Andre Pany wrote:




what result u expecting?

u send from "b": e1 10 e2 9
"a" read it. 1st loop finished.
then u send from "b" p.stdout.readln(); that is read as 2nd 
enemy1=null
and finally sleep and exit from b.main where pipe is closed and 
"a" read null again (no data)
dist1 = null.to!int => error
Aug 27 2019
parent a11e99z <black80 bk.ru> writes:
On Tuesday, 27 August 2019 at 21:28:05 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 21:01:58 UTC, Andre Pany wrote:

 On Tuesday, 27 August 2019 at 20:45:44 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 20:09:34 UTC, Andre Pany wrote:




 what result u expecting?

 then u send from "b" p.stdout.readln(); that is read as 2nd


its not sent, "b" just read from pipe
pipe closed and null (no data) come to "a"
Aug 27 2019
prev sibling parent reply a11e99z <black80 bk.ru> writes:
On Tuesday, 27 August 2019 at 21:01:58 UTC, Andre Pany wrote:

 On Tuesday, 27 August 2019 at 20:45:44 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 20:09:34 UTC, Andre Pany wrote:

 






"b" should send data in loop too, then "a" will work ok.
do u still hack CodinGame? :)
Aug 27 2019
parent Andre Pany <andre s-e-a-p.de> writes:
On Tuesday, 27 August 2019 at 21:42:55 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 21:01:58 UTC, Andre Pany wrote:

 On Tuesday, 27 August 2019 at 20:45:44 UTC, a11e99z wrote:

 On Tuesday, 27 August 2019 at 20:09:34 UTC, Andre Pany wrote:

 






 "b" should send data in loop too, then "a" will work ok.
 do u still hack CodinGame? :)


Thanks for the answers. I currently try to make the Codingame 
puzzles available for D by writing a local application which has 
similar puzzles and runs the D source code.

Kind regards
Andre
Aug 27 2019