(New to C++)
I have this simple code (simplified for the question):
int main()
{
string currInput;
while (getline(cin, currInput))
{
}
cout << "wont be printed" << std::flush;
return 0;
}
I have been debugging for a while and I probably miss something:
When running it and pressing ctrl+d (after some strings or right away), it does not print the string that is after the while loop. It just stop running. I thought it might be something with flushing so I added that too.
What am I missing?
PS: When running in debug, it mentions something about sighup signal.
So, with a lot of help from #manni and #rici, we found the problem.
It turns out to be a known problem in cLion.
see sending EOF to stdin in Clion IDE
https://intellij-support.jetbrains.com/hc/en-us/community/posts/206849765-How-to-enter-EOF-Ctrl-z-in-Run-console-
https://youtrack.jetbrains.com/issue/IDEA-12514
Your error is the while loop. You should not be using a loop here. What happens is it hits this line and attempts to get input. Regardless of whether you type in anything or not, if you hit CTRL+D it will end the getline. But you have it in a while loop....so it'll hop back to the top of the loop and get another line...then another line....then another line. Welcome to your first infinite loop.
while (getline(cin, currInput))
{
}
The simplest thing would be to do just
getline(cin, currInput);
If you're starting out programming this is probably what you want to do anyway.
If you feel gutsy, read this page: http://www.cplusplus.com/reference/string/string/getline/
You'll notice that getline returns the stream you pass in. Which will evaluate to true as far the loop is concerned.
Lately, I've been trying to learn C++ from this website. Unfortunately whenever I try to run one of the code samples, I see that program open for about a half second and then immediately close. Is there a way to stop the program from closing immediately so that I can see the fruits of my effort?
If you are using Visual Studio and you are starting the console application out of the IDE:
pressing CTRL-F5 (start without debugging) will start the application and keep the console window open until you press any key.
Edit: As Charles Bailey rightly points out in a comment below, this won't work if there are characters buffered in stdin, and there's really no good way to work around that. If you're running with a debugger attached, John Dibling's suggested solution is probably the cleanest solution to your problem.
That said, I'll leave this here and maybe someone else will find it useful. I've used it a lot as a quick hack of sorts when writing tests during development.
At the end of your main function, you can call std::getchar();
This will get a single character from stdin, thus giving you the "press any key to continue" sort of behavior (if you actually want a "press any key" message, you'll have to print one yourself).
You need to #include <cstdio> for getchar.
The solution by James works for all Platforms.
Alternatively on Windows you can also add the following just before you return from main function:
system("pause");
This will run the pause command which waits till you press a key and also displays a nice message Press any key to continue . . .
If you are using Microsoft's Visual C++ 2010 Express and run into the issue with CTRL+F5 not working for keeping the console open after the program has terminated, take a look at this MSDN thread.
Likely your IDE is set to close the console after a CTRL+F5 run; in fact, an "Empty Project" in Visual C++ 2010 closes the console by default. To change this, do as the Microsoft Moderator suggested:
Please right click your project name and go to Properties page, please expand Configuration Properties -> Linker -> System, please select Console (/SUBSYSTEM:CONSOLE) in SubSystem dropdown. Because, by default, the Empty project does not specify it.
I usually just put a breakpoint on main()'s closing curly brace. When the end of the program is reached by whatever means the breakpoint will hit and you can ALT-Tab to the console window to view the output.
Why not just run the program from a console ie run the program from cmd.exe if you're using Windows. That way the window stays open after the program finishes.
[EDIT]: When I use KDevelop4 there is a fully fledged instance of Bash (a Linux CLI) running in a tab at the bottom of the IDE. Which is what I use in these sort of circumstances.
Before the end of your code, insert this line:
system("pause");
This will keep the console until you hit a key.
#include <iostream>
#include <string>
using namespace std;
int main()
{
string s;
cout << "Please enter your first name followed by a newline\n";
cin >> s;
cout << "Hello, " << s << '\n';
system("pause"); // <----------------------------------
return 0; // This return statement isn't necessary
}
Call cin.get(); 2 times:
//...
cin.get();
cin.get();
return 0
}
If you run your code from a competent IDE, such as Code::Blocks, the IDE will manage the console it uses to run the code, keeping it open when the application closes. You don't want to add special code to keep the console open, because this will prevent it functioning correctly when you use it for real, outside of the IDE.
I just do this:
//clear buffer, wait for input to close program
std::cin.clear(); std::cin.ignore(INT_MAX, '\n');
std::cin.get();
return 0;
Note: clearing the cin buffer and such is only necessary if you've used cin at some point earlier in your program. Also using std::numeric_limits::max() is probably better then INT_MAX, but it's a bit wordy and usually unnecessary.
Okay I'm guessing you are on Windows using Visual Studio... why? Well because if you are on some sort of Linux OS then you'd probably be running it from the console.
Anyways, you can add crap to the end of your program like others are suggesting, or you can just hit CTRL + F5 (start without debugging) and Visual Studio will leave the console up once complete.
Another option if you want to run the Debug version and not add crap to your code is to open the console window (Start -> Run -> cmd) and navigate to your Debug output directory. Then, just enter the name of your executable and it will run your debug program in the console. You can then use Visual Studio's attach to process or something if you really want to.
Just add the following at the end of your program. It will try to capture some form of user input thus it stops the console from closing automatically.
cin.get();
If you are actually debugging your application in Visual C++, press F5 or the green triangle on the toolbar. If you aren't really debugging it (you have no breakpoints set), press Ctrl+F5 or choose Start Without Debugging on the menus (it's usually on the Debug menu, which I agree is confusing.) It will be a little faster, and more importantly to you, will pause at the end without you having to change your code.
Alternatively, open a command prompt, navigate to the folder where your exe is, and run it by typing its name. That way when it's finished running the command prompt doesn't close and you can see the output. I prefer both of these methods to adding code that stops the app just as its finished.
Add the following lines before any exit() function or before any returns in main():
std::cout << "Paused, press ENTER to continue." << std::endl;
cin.ignore(100000, "\n");
For Visual Studio (and only Visual Studio) the following code snippet gives you a 'wait for keypress to continue' prompt that truly waits for the user to press a new key explicitly, by first flushing the input buffer:
#include <cstdio>
#include <tchar.h>
#include <conio.h>
_tprintf(_T("Press a key to continue "));
while( _kbhit() /* defined in conio.h */ ) _gettch();
_gettch();
Note that this uses the tchar.h macro's to be compatible with multiple 'character sets' (as VC++ calls them).
Use #include "stdafx.h" & system("pause"); just like the code down below.
#include "stdafx.h"
#include <iostream>
using namespace std;
int main()
{
std::cout << "hello programmer!\n\nEnter 2 numbers: ";
int x, y;
std::cin >> x >> y;
int w = x*y;
std::cout <<"\nyour answer is: "<< w << endl;
system("pause");
}
simply
#include <cstdio>
int main(){
// code...
std::getchar();
std::getchar();
return 0;
}
for some reason there is usually 1 character possible to read with getchar already in stdin when you run a program. so the first getchar reads this character, and the second getchar waits for user (your) input before exiting the program. And after a program exits most of terminals, especially on Windows close terminal immediately.
so what we aim to is a simple way of preventing a program from finishing after it outputs everything.
Of course there are more complex and clean ways to solve this, but this is the simplest.
Similar idea to yeh answer, just minimalist alternative.
Create a batch file with the following content:
helloworld.exe
pause
Then use the batch file.
See if your IDE has a checkbox in project setting to keep the window open after the program terminates. If not, use std::cin.get(); to read a character at the end of main function. However, be sure to use only line-based input (std::getline) or to deal with leftover unread characters otherwise (std::ignore until newline) because otherwise the .get() at the end will only read the garbage you left unread earlier.
This seems to work well:
cin.clear();
cin.ignore(2);
If you clear the buffer first it won't be a problem when you read the next one.
For some reason cin.ignore(1) does not work, it has to be 2.
You could always just create a batch file. For example, if your program is called helloworld.exe, some code would be:
#echo off
:1
cls
call helloworld.exe
pause >nul
goto :1
If you are running Windows, then you can do system("pause >nul"); or system("pause");. It executes a console command to pause the program until you press a key. >nul prevents it from saying Press any key to continue....
I'm putting a breakpoint at the last return 0 of the program. It works fine.
I used cin.get() and that is worked but one day I needed to use another cin.get([Array Variable]) before that to grab a ling string with blank character in middle of. so the cin.get() didn't avoid command prompt window from closing. Finally I found Another way:
Press CTRL+F5 to open in an external window and Visual Studio does not have control over it anymore. Just will ask you about closing after final commands run.
I tried putting a getchar() function at the end. But it didn't work. So what I did was add two getchar() functions one after another. I think the first getchar() absorbs the Enter key you press after the last data input. So try adding two getchar() functions instead of one
Instead of pressing the run button, press CTRL and F5 at the same time, it will give you the press any key to continue message. Or type "(warning use this only for testing not actual programs as an antiviruses don't like it!!!!)" at the end of your main function but: (warning use this only for testing not actual programs as an antiviruses don't like it!!!!)
just use cin.ignore() right before return 0; twice
main()
{
//your codes
cin.ignore();
cin.ignore();
return 0;
}
thats all
you can try also doing this
sleep (50000);
cout << "any text" << endl;
This will hold your code for 50000m, then prints message and closes. But please keep in mind that it will not pause forever.
Here's a problem, not so obvious. Somehow I had added a debug breakpoint at the very last line of my program. } Not sure how I did that, perhaps with an erroneous mouse click while jumping between different screens. I'm working in VS Code.
And when I go to debug, the system jumps immediately to that breakpoint. No error message, no interim output, nothing. I'm like, how did the program rush thru all my set breakpoints? This took too long to figure out.
Apparently the system sees that last line breakpoint as a "first" stop. The simple fix? Delete that breakpoint, doh! (insert forehead slap here.)
All you have to do set a variable for x then just type this in before the return 0;
cout<<"\nPress any key and hit enter to end...";
cin>>x;
I'm new to code and this website, so please forgive me if I'm overlooking something obvious. I've been trying to write a short little game in c++, and I need to take in user input. I want to take in more than one word so the cin>> command my book recommends is right out. The best thing I have found through research is the getline(cin,var); command. I can get this to easily work in small scale tests, but when I implement it in to my 500 line game, it never works. It will skip right over that bit of code without waiting for user imput, and set the variable to a blank space. I won't include the whole code obviously, but here is the bit in question, and my headers.
#include <cstdlib>
#include <windows.h>
#include <iostream>
#include <string>
using namespace std;
string poemend;
int heading;
int poem()
{
system("CLS");
cout<<"This poem is almost done, you just can't seem to find the perfect last word.\n";
cout<<"You can see several of your discarded endings. Most recently, 'pain'.\n\n";
cout<<"How about another go?\n>";
getline(cin,poemend);
system("CLS");
cout<<"The Prophet's old parrot spoke much of all things,\n";
cout<<"but when asked about love, squawked only ";
cout<<poemend<<" .\n\n";
Sleep(6000);
cout<<"You decide it could still use some work";
Sleep(3000);
heading = 6;
}
Again, this works perfectly if I take this in to a new blank page, so I'm really not sure what is getting in the way. I will be happy to answer any questions about the code and post more helpful bits of it if needed. Thank you so much for taking the time to read this!
Sometimes flushing the input buffer is magic. This may or may not be the case in your senario, but try this code.
cin.ignore( cin.rdbuf()->in_avail() );
cin.getline(cin,poemend);
cin.clear();
Essentially wrapping your getline with the ignore code and cin.clear.
You still have a newline which is the residue of a previous unformatted input operation. You have to discard it using std::ws. Moreover, always check if your input succeeded:
if (std::getline(std::cin >> std::ws, poemend))
// ^^^^^^^^^^^^^^^^^^^
I mam trying to complete a college assignment in C++ and am having trouble with what should be a very basic operation. I am trying to read a string of characters from the keyboard. This is the relevant code:
string t;
cout << endl << "Enter title to search for: ";
getline(cin, t, '\n');
I understand, that the last line is supposed to read the input buffer (cin , in this instance) and store the character in the 't' string until it reaches a new line character and then continue the program flow.
However, when I run my code in XCode, it just sort of jumps over the getline function and treats 't' as an empty string.
What's going on? I tried using cin >> t but that just read characters forever - Why cant I get this to behave?
The reason that the input operation apparently is skipped, is most probably (that means, ignoring possible peculiarities of a bugsy XCode IDE) that you have performed some input earlier and left a newline in the input buffer.
To fix that, make sure that you have emptied the input buffer after each input operation that logically should consume a line of input.
One easy way is to always use getline into a string, and then use e.g. an istringstream if you want to convert a number specification to number type.
Cheers & hth.,
From the docs page it looks like you want
cin.getline(t,256,'\n');
or something similar.
This sounds like an issue with the way Xcode is running your program. Try running your program directly from the terminal, and see if this is sufficient to fix your issue.
I am working on a simple application written in C. I am working in a Unix environment.
My application is doing some simple I/O. I use printf to prompt the user for some input and then use scanf to get that input.
The problem is, I don't know how to tell my application that I am ready to proceed after entering in a value. Typing 'enter' provides a newline '\n' which makes sense. Control-d does allow scanf to capture my input but seems to ignore any subsequent scanf instructions.
Can someone help me out?
printf("Enter name\n");
scanf("%s",input);
printf("%s",input);
printf("enter more junk\n")
scanf("%s",morestuff); /* cntrl+d skips this*/
Check the return value from scanf(). Once it has gotten EOF (as a result of you typing control-D), it will fail each time until you clear the error.
Be cautious about using scanf(); I find it too hard to use in the real world because it does not give me the control over error handling that I think I need. I recommend using fgets() or an equivalent to read lines of data, and then use sscanf() - a much more civilized function - to parse the data.
See also a loosely related question: SO 3591642.
[EDIT: This answer is incorrect, as I stated below, I'm learning as well]
Have you tried CTRL-Z?
That sends EOF to scanf, which, according to its man page, should make scanf move to the next field. As you've entered only a string as the input format, that should terminate the scanf.
I can't test this right now, but you can give it a shot.
Man page is here:
http://www.slac.stanford.edu/comp/unix/package/rtems/doc/html/libc/libc.info.scanf.html