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digitalmars.D.learn - how stdin stream works?

reply Flade <consolemaster0 gmail.com> writes:
Hi everyone! I'm trying to do error handling (with the try block) 
and when I give a wrong value to the variable (it is an integer 
and I give a non-number value), then It doesn't let me re get 
input. The code:


int x;

bool not_accepted = false;

while (!not_accepted) {

     try {

         write("x: ");

         readf("%d\n", x);

         not_accepted = true;

} catch (Exception msg) {

         writeln("Please give a right coordinate");

     }
Aug 19 2020
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 8/19/20 1:44 PM, Flade wrote:

 Hi everyone! I'm trying to do error handling (with the try block) and 
 when I give a wrong value to the variable (it is an integer and I give a 
 non-number value), then It doesn't let me re get input. The code:
 
 
 int x;
 
 bool not_accepted = false;
 
 while (!not_accepted) {
 
      try {
 
          write("x: ");
 
          readf("%d\n", x);
 
          not_accepted = true;
 
 } catch (Exception msg) {
 
          writeln("Please give a right coordinate");
 
      }


Probably readf stops as soon as it encounters an error, meaning that 
your input is still present.

Try instead getting a line via readln, and then trying to read that into 
your expected input.

-Steve
Aug 19 2020
parent reply Flade <consolemaster0 gmail.com> writes:
On Wednesday, 19 August 2020 at 18:11:23 UTC, Steven 
Schveighoffer wrote:

 On 8/19/20 1:44 PM, Flade wrote:

 Hi everyone! I'm trying to do error handling (with the try 
 block) and when I give a wrong value to the variable (it is an 
 integer and I give a non-number value), then It doesn't let me 
 re get input. The code:
 
 
 int x;
 
 bool not_accepted = false;
 
 while (!not_accepted) {
 
      try {
 
          write("x: ");
 
          readf("%d\n", x);
 
          not_accepted = true;
 
 } catch (Exception msg) {
 
          writeln("Please give a right coordinate");
 
      }


 Probably readf stops as soon as it encounters an error, meaning 
 that your input is still present.

 Try instead getting a line via readln, and then trying to read 
 that into your expected input.

 -Steve


Thanks Steve! I will get the input a string then as you said and 
then I'll try to convert it! Thanks a lot, have a nice day!
Aug 19 2020
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 8/19/20 11:46 AM, Flade wrote:


 Try instead getting a line via readln, and then trying to read that 
 into your expected input.

 -Steve


 
 Thanks Steve! I will get the input a string then as you said and then 
 I'll try to convert it! Thanks a lot, have a nice day!


In some cases clearerr() and readln() may be what is needed:

import std.stdio;

void main() {
   int x;

   bool accepted = false;

   while (!accepted) {
     try {
       write("x: ");
       readf(" %d", x);
       accepted = true;

     } catch (Exception msg) {

       writeln("Please give a right coordinate");
       stdin.clearerr();
       stdin.readln();
     }
   }

   writeln("x is ", x);
}

Note that I used " %d" because "%d/n" would not clean when nothing was 
input by just hitting the Enter key. A space character in the format 
string means "read and ignore any whitespace at this point" and I like 
it. :)

Also note I changed the name of the variable as 'accepted'. :)

Ali
Aug 20 2020
next sibling parent Flade <consolemaster0 gmail.com> writes:
On Thursday, 20 August 2020 at 19:13:31 UTC, Ali Çehreli wrote:

 On 8/19/20 11:46 AM, Flade wrote:


 [...]


 In some cases clearerr() and readln() may be what is needed:

 import std.stdio;

 void main() {
   int x;

   bool accepted = false;

   while (!accepted) {
     try {
       write("x: ");
       readf(" %d", x);
       accepted = true;

     } catch (Exception msg) {

       writeln("Please give a right coordinate");
       stdin.clearerr();
       stdin.readln();
     }
   }

   writeln("x is ", x);
 }

 Note that I used " %d" because "%d/n" would not clean when 
 nothing was input by just hitting the Enter key. A space 
 character in the format string means "read and ignore any 
 whitespace at this point" and I like it. :)

 Also note I changed the name of the variable as 'accepted'. :)

 Ali


Thanks a lot! Very useful info!!! And sorry for answering so 
late, I wasn't expecting someone to answer so I wasn't checking. 
Have a great day my friend!
Aug 23 2020
prev sibling parent Flade <consolemaster0 gmail.com> writes:
On Thursday, 20 August 2020 at 19:13:31 UTC, Ali Çehreli wrote:

 On 8/19/20 11:46 AM, Flade wrote:


 [...]


 
 Thanks Steve! I will get the input a string then as you said 
 and then I'll try to convert it! Thanks a lot, have a nice day!


 In some cases clearerr() and readln() may be what is needed:

 import std.stdio;

 void main() {
   int x;

   bool accepted = false;

   while (!accepted) {
     try {
       write("x: ");
       readf(" %d", x);
       accepted = true;

     } catch (Exception msg) {

       writeln("Please give a right coordinate");
       stdin.clearerr();
       stdin.readln();
     }
   }

   writeln("x is ", x);
 }

 Note that I used " %d" because "%d/n" would not clean when 
 nothing was input by just hitting the Enter key. A space 
 character in the format string means "read and ignore any 
 whitespace at this point" and I like it. :)

 Also note I changed the name of the variable as 'accepted'. :)

 Ali


Wait! Oh man I just checked your name!!!! I'm currently reading 
your book and I wanted to say that you did an EXCELLENT work and 
I love it! Thanks a lot! You are great!!!
Aug 23 2020