I am currently reading K&R's book and typing in the examples from the first section, and there are a couple of examples such as this:
while((c = getchar()) != EOF) {
//do something
}
I am testing these examples on a Windows box and thus running the compiled exe files from the cmd prompt.
To test the example above, how do I simulate an EOF? That is, basically how can I make the loop stop when testing the example from the command prompt?
To enter an EOF, use:
^Z (CtrlZ) in Windows
^D on Unix-like systems
Refer EOF
Windows: Ctrl+Z
Unix :Ctrl+D
First, press: Ctrl^X, next: Ctrl^D
You can also simulate EOF by explicitly giving int variable a value of -1.
Check out this code for more clarity:
#include<stdio.h>
int main() {
// char ch=getchar()
// int ch=-1;
if(ch==EOF) { printf("\nEOF: %d",EOF); }
if((ch!=EOF)==0) { printf("\nit is equal to 0"); }
if((ch!=EOF)==1) { printf("\nit is equal to 1"); }
else { printf("\n it is equal to other value"); }
system("pause");
return 0;
}
I had the same problem after pressing Ctrl+d program stopped and returned 0.
If you use Clion press Ctrl+Shift+a than type Registry press enter and make sure run.processes.with.pty. is unchecked.
After that compile program again and then you can type in input but don't press Ctrl+d on the same line as input it will return 0 or Error.
Related
I am currently reading K&R's book and typing in the examples from the first section, and there are a couple of examples such as this:
while((c = getchar()) != EOF) {
//do something
}
I am testing these examples on a Windows box and thus running the compiled exe files from the cmd prompt.
To test the example above, how do I simulate an EOF? That is, basically how can I make the loop stop when testing the example from the command prompt?
To enter an EOF, use:
^Z (CtrlZ) in Windows
^D on Unix-like systems
Refer EOF
Windows: Ctrl+Z
Unix :Ctrl+D
First, press: Ctrl^X, next: Ctrl^D
You can also simulate EOF by explicitly giving int variable a value of -1.
Check out this code for more clarity:
#include<stdio.h>
int main() {
// char ch=getchar()
// int ch=-1;
if(ch==EOF) { printf("\nEOF: %d",EOF); }
if((ch!=EOF)==0) { printf("\nit is equal to 0"); }
if((ch!=EOF)==1) { printf("\nit is equal to 1"); }
else { printf("\n it is equal to other value"); }
system("pause");
return 0;
}
I had the same problem after pressing Ctrl+d program stopped and returned 0.
If you use Clion press Ctrl+Shift+a than type Registry press enter and make sure run.processes.with.pty. is unchecked.
After that compile program again and then you can type in input but don't press Ctrl+d on the same line as input it will return 0 or Error.
I have this code. what I want to do is to wait for user to press 'q' to end the program.
.
...starting few threads, which use fflush(stdout) (just saying...)
.
char n = 0;
while (n != 'q') {
n = getchar(); //tried to use scanf() here as well
printf("%c", n);
}
...killing all threads...
return 0;
When I run this in a normal Linux enviroment it works fine.
The problem starts when I run this program at startup on my raspberry-pi with debian jessie lite distribution (I added the path to the program to /etc/rc.local) - it ends in an infinite loop, scanf is still returning -1 and getchar() some weird character and the program won't end, when I press q. Ctrl+C doesn't work either so there is no way, how to end the program.
Any suggestions? (at least how to kill the program...?)
Edit: To let you know what the program does.
Raspberry-pi with this program is attached to some serial ports and converts and transfers some GPS data. It should work "out of the box" without any keyboard or mouse or monitor. = Just plug the device to some cables and do nothing more. In some cases someone would like to see log files on the raspberry, so he needs to stop the program, obviously.
Edit2: when I did the same with some normal Raspbian, it worked fine too.
Update:
I tried to debug it - shrinked the code to this only
int main(void){
char n=0;
int x;
while (n != 'q'){
clearerr(stdin);
x=scanf("%c",&n);
printf("%c %d\n",n,x);
}
return 0;
}
added service start udev to rc.local and tried command update.rc.d udev enable
output on raspberry-pi when launched at startup is still
-1
-1
-1
.
.
so there definitely have to be something wrong with stdin.
After startup and on other systems, the output is obviously q 1 (when I press 'q' (and enter) ...)
when I tried to read from /dev/tty, fopen() returned NULL
Really need a help with this
The idiomatic way to write this loop is:
int c;
while ((c = getchar()) != EOF && c != 'q'){
putchar(c);
}
Your implementation cannot detect end of file and will loop forever, printing funny characters such as ΓΏ.
Just a wild guess that stdin maybe redirected to something else and you need to read from keyboard directly. try the following code:
FILE *tty = fopen("/dev/tty", "r");
if (!tty) {
exit(1);
}
int n=0;
while (n != 'q'){
n=fgetc(tty); //tried to use scanf() here as well
printf("%c",(char)n);
}
I am creating some library function for print and scan using assembly language and c.
Now when am entering datas it is getting print,but the problem is when i press the backspace button the cursor is moving backwards(but not deleting anything)..I want the backspace button to work properly(ie,to delete the previous character)
so is there any program for that.Please help me.
The simple, albeit somewhat hackish, way is to just write backspace characters (\b) to the console.
For example:
#include <stdio.h>
int main()
{
printf("Testing");
fflush(stdout);
printf("\b\b\b");
fflush(stdout);
return 0;
}
But this type of thing should really be handled by your terminal driver. You don't mention what operating system you're targeting in the question.
Output a backspace, space, and backspace:
int c = getchar();
if (c == '\b')
{
printf("\b \b");
fflush(stdout);
}
If the user's press of a backspace was already echoed by the terminal driver then just do this:
int c = getchar();
if (c == '\b')
{
printf(" \b");
fflush(stdout);
}
if u r doing so then would like to tell you one thing abt consoles
There are 2 types of consoles , one which can recognize control char. called
Active console(Canonical mode) and one which not called row console .
Obviously if u r using unix's terminal then u will be given default as Active mode console
but u can set it to row mode by executing some commands.
I wrote a program to count blanks. I can compile it and run it, it's fine. But why it does not display the count?
#include<stdio.h>
main()
{
int count=0;
int c;
while((c=getchar())!=EOF)
{
if(c == ' ') count++;
}
printf("%d\n",count);
}
Your exact code (errors and all) works as you'd expect at ideone.
How do you terminate the input? To send an EOF signal to your program from the console type, at the beginning of a line, CtrlD in Linux or CtrlZ in Windows.
Also try to run with redirected input. Something like
yourprog < data.txt
or
echo one two three four | yourprog
You're probably not getting the EOF that you expect from input. You may be expecting the Enter key to be EOF, which will not happen. Have you tried using one of the ctrl+ combinations such as Z or D (depending on OS) to send the EOF ?
Right now I am going through a book on C and have come across an example in the book which I cannot get to work.
#include <stdio.h>
#define IN 1
#define OUT 0
main()
{
int c, nl, nw, nc, state;
state = OUT;
nl = nw = nc = 0;
while ((c = getchar()) != EOF) {
++nc;
if (c == '\n')
++nl;
if (c == ' ' || c == '\n' || c == '\t')
state = OUT;
else if (state == OUT) {
state = IN;
++nw;
}
}
printf("%d %d %d\n", nl, nw, nc);
}
It's supposed to count the number of lines, words, and characters within an input. However, when I run it in the terminal it appears to do nothing. Am I missing something or is there a problem with this code?
The program only terminates when the input ends (getchar returns EOF). When running on terminal, this normally never happens and because of this it seems that the program is stuck. You need to close the input manually by pressing Ctrl+D (possibly twice) on Linux or pressing F6 and Enter at the beginning of the line on Windows (different systems may use different means for this).
It's waiting for input on stdin. Either redirect a file into it (myprog < test.txt) or type out the data and hit Ctrl-D (*nix) or Ctrl-Z (Windows).
When you run it, you need to type in your text, press return, then type Ctrl-d and return (nothing else on the line) to signify end-of-file. Seems to work fine with my simple test.
What it is doing is entering a loop for input. If you enter a character or newline, nothing happens on the screen. You need to interrupt the process (on my Mac this is CTRL+D) which serves as EOF. Then, you will get the result.
getchar() returns the input from the standard input. Start typing the text for which you want to have the word count and line count. Your input terminates when EOF is reached, which you do by hitting CTRL D.
CTRL D in this case acts as an End Of Transmission character.
cheers
I usually handle this kind of input like this (for Linux):
1. make a file (for example, named "input.txt"), type your input and save
2. use a pipe to send the text to your application (here assume your application named "a.out" and in the current directory):
cat input.txt | ./a.out
you'll see the program running correctly.