Press any key to continue...

03 July 2014

Background

For CLI console programs, we need some mechanims to pause execution and continue as convenient as possible.

While scanf() alike functions can do part of the work, it forces Enter.

Our key here is any.

Solutions

#1 pause

This is the easiest one.

main.c

#include <stdlib.h>
#include <stdio.h>

int main(int argc, char *argv[]) {
	system("pause");
	return EXIT_SUCCESS;
}

Let’s build and run it.

$ gcc main.c
$ ./a.out

But only works when pause utility is available, which is provided by default under Windows.

Press any key to continue...

The pause command handles not only the hint message, but also i18n, e.g. on zh_CN machines:

请按任意键继续. . .

If not, you’re likely be prompted the following error message:

pause: command not found

#2 getch

This is a secondary choice.

main.c

#include <stdlib.h>
#include <stdio.h>
#include <conio.h>

int main(int argc, char *argv[]) {
	printf("Press any key to continue...");
	getch();
	return EXIT_SUCCESS;
}

Build and run as above.

Note that the application if responsible for prompt message.

Also, conio.h header is not mandatory on some OSes, which will cause:

main.c:3:10: fatal error: 'conio.h' file not found
#include <conio.h>
         ^
1 error generated.

#3 posix

When there’s no gun in our hand, we’ll make our own.

main.c

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

static int get_ch();

int main(int argc, char *argv[]) {
	printf("Press any key to continue...\n");
	get_ch();
	return EXIT_SUCCESS;
}

static int get_ch() {
	int c;
	int fd = STDIN_FILENO;
	struct termios tm;
	struct termios tm_old;

	if (tcgetattr(fd, &tm) < 0) {
		return -1;
	}

	tm_old = tm;
	cfmakeraw(&tm);

	if (tcsetattr(fd, TCSANOW, &tm) < 0) {
		return -1;
	}

	c = fgetc(stdin);

	if (tcsetattr(fd, TCSANOW, &tm_old) < 0) {
		return -1;
	}

	return c;
}

Build and run as above.

This is a general choice, as long as the OS is POSIX compatible.

Choice

Which one to choose? It’s in your own hand.

Programs 8