Question

I’m trying to make a simple command that pauses for user input. I think it’ll be useful in Bash scripts.

Here’s my code:

#include <stdio.h>
int main() {
  char key[1];
  puts("Press any key to continue...");
  fgets(key,1,stdin);
}

It doesn’t even pause for user input.

I tried earlier to use getch() (ncurses). What happened is, the screen went blank and when I pressed a key, it went back to what was originally on the screen, and I saw:

$ ./pause
Press any key to continue...
$

It’s somewhat what I wanted. But all I want is the equivalent of the pause command in DOS/Windows (I use Linux).

Answer 1

From the GNU C Library Manual:

Function: char * fgets (char *s, int count, FILE *stream)

The fgets
function reads characters from the stream stream up to and including a
newline character and stores them in the string s, adding a null
character to mark the end of the string. You must supply count
characters worth of space in s, but the number of characters read is
at most count − 1. The extra character space is used to hold the null
character at the end of the string.

So, fgets(key,1,stdin); reads 0 characters and returns. (read: immediately)

Use getchar or getline instead.

Edit: fgets also doesn’t return once count characters are available on the stream, it keeps waiting for a newline and then reads count characters, so "any key" might not be the correct wording in this case then.

You can use this example to avoid line-buffering:

#include <stdio.h>
#include <termios.h>
#include <unistd.h>

int mygetch ( void ) 
{
  int ch;
  struct termios oldt, newt;
  
  tcgetattr ( STDIN_FILENO, &oldt );
  newt = oldt;
  newt.c_lflag &= ~( ICANON | ECHO );
  tcsetattr ( STDIN_FILENO, TCSANOW, &newt );
  ch = getchar();
  tcsetattr ( STDIN_FILENO, TCSANOW, &oldt );
  
  return ch;
}

int main()
{
    printf("Press any key to continue.\n");
    mygetch();
    printf("Bye.\n");
}