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I am trying to make a small program that includes an infinite loop to wait for signal input from the user. I wanted to print out a message about the current working directory before beginning the infinite loop. The message works on its own, but when I put the infinite loop into the code the message does not print out (but the terminal does loop infinitely). The code is:
#include <stdio.h>
int MAX_PATH_LENGTH = 100;
main () {
char path[MAX_PATH_LENGTH];
getcwd(path, MAX_PATH_LENGTH);
printf("%s> ", path);
while(1) { }
}
If I take out while(1) { } I get the output:
ad@ubuntu:~/Documents$ ./a.out
/home/ad/Documents>
Why is this? Thank you!
387
Printf is not the thing being buffered, it's stdio, so all similar functions will behave in the same way. To demonstrate the buffering, all you have to do is printf a lot of characters, usually more than 1024, and printf will print as you will have exceeded the maximum buffer length and it will automatically fflush.
In order to come out of the infinite loop, we can use the break statement. Let's understand through an example. In the above code, we have defined the while loop, which will execute an infinite number of times until we press the key 'n'. We have added the 'if' statement inside the while loop.
The printf statement does not automatically append a newline to its output. It outputs only what the format string specifies. So if a newline is needed, you must include one in the format string.
Next we write the c code to create the infinite loop by using while loop with the following example. As in the above code while loop runs infinite times because the condition always becomes true and the i value is updated infinite times.
When you call printf, the output doesn't get printed immediately; instead, it goes into a buffer somewhere behind the scenes. In order to actually get it to show up on the screen, you have to call fflush or something equivalent to flush the stream. This is done automatically for you whenever you print a newline character* and when the program terminates; it's that second case that causes the string to show up when you remove the infinite loop. But with the loop there, the program never ends, so the output never gets flushed to the screen, and you don't see anything.
*As I just discovered from reading the question itsmatt linked in a comment, the flush-on-newline only happens when the program is printing to a terminal, and not necessarily when it's printing to a file.
79
Because you don't have a new-line character at the end of your string. stdout is line-buffered by default, which means it won't flush to console until it encounters a new-line character ('\n'), or until you explicitly flush it with fflush().
37
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