System("read") command

Question

Hello. I've got the following code in a program:
printf("%s", "the text that I want to print to the console");
system("read");
The purpose here is to have the text from the printf( ) statement above print to the console, and then have the program pause and wait for the user to hit any key (note that scanf( ) or other input functions are not appropriate here for two reasons: first, the keys the user hits actually appear on the console, and I don't want them to, and second, the user can type many, many keys and the program will not continue until he or she hits Enter -- I want the program to simply pause until any key is hit). I knew that with C++ on Windows I used to be able to achieve this perfectly using system("Pause"), but I found that this did not work with C on the Mac. Thanks to help from RayNewb and Cohi in a previous thread, they explained that system( ) was a stdlib.h function that could easily be used in C, and that I just needed to find the Unix-equivalent of the "Pause" command (which was a DOS command, which is why it wasn't working on the Mac). Ray and Cohi came up with the following statement to replace the DOS-oriented system("Pause"):
system( "read -n 1 -s -p "Press any key to continue..."; echo" );
As you can see from the code at the very top of the post, I ended up shortening this statement to simply system("read") because I found that, for my purposes at least, it did the exact same thing as the longer version shown directly above. In either case, they were right about this command, and this statement did exactly what I wanted it to, except for one problem...
Gievn the two statements at the top of the post, the expected result would be for the text from the printf( ) statement to print to the console, followed by a pause in the program waiting for a key to be hit, at which point the program would continue. This is exactly what happens, only backwards. The program starts off with a pause, waiting for any key to be hit, and when a key is hit, only then does the printf( ) statement run and the text appear on the console. This happens whether I use the short version of the "read" statement or the full version that Ray and Cohi came up with. Can anyone help explain this? Any help is greatly appreciated.

Answer 1

Tron55555 wrote:
I know the fprintf() function, but I thought it was only used to write to files
Important plot point - everything is a file.
What is it that allows "stdout" to be used in place of a file name in this function's argument? Since "stdout" is a pointer like you said, does that mean that any pointer could be used for the first argument in the fprintf() function, not just file pointers? How's that work?
fprintf doesn't take a file name. It takes a "FILE *". You can create one of those with "fopen()" or you can use the pre-defined ones for standard input, output, and error. You can use any valid "FILE *" for the argument.
Do you guys have any recommendation of which would be better (whether it would be better to use fflush(stdout) or fprintf(stderr, "") )? Is one of these solutions more appropriate than the other, or are they both the same in effect?
Neither. Don't write command-line tools that depend on the terminal. fflush(stdout) is more tedious to use in the code, but more robust. Otherwise, you would have some of your output going to stdout and some of it going to stderr, which becomes a hassle. But it is only a hassle when you are dealing with command-line tools that are using the command line as an interface, and those things are always a hassle. It is better to stick to stdout and then you can more easily pipe the output of one program to the input of another. If you are going to break that functionality, you might as well write a real GUI. If you do your command-line tool correctly, you can easily write a GUI wrapper for it and have both GUI and good command-ilne functionality.
I don't really know anything about this stuff, but you mentioned that it's generally a bad idea to write command-line apps that have dependencies on the Terminal. Do you know of any other way to achieve the type of pause I'm trying to achieve without using the Terminal?
No. If you want to have a user interface, you have to interact. Unix was designed around the idea of a toolbox of simple programs that can be combined (piped) together to do clever things. You shouldn't have a requirement for terminal interaction. The basic functionality should be entirely driven by the command line so your tool could be easily used by other tools. If you really want an interface, add one, but require a "-i" flag to trigger interactive mode or maybe use "isatty()" to find out automatically (The "i" flag would be more robust though).
Consider the shell itself. It is, by definition, an interactive program. Right? Wrong. It can be run non-interactively too. In fact, non-interactive behavior is the default.
I've heard of them before, but don't know anything about them. If anyone has spare time, could you give me an explanation of what they do (doesn't have to be anything in detail -- just tyring to get some really basic idea of what they are, and what all the fuss over them is about). Thanks for your reply, eric.
It is an easy to use library for (fully) interacting with the terminal. It was a bigger deal before everyone had graphical user interfaces. There are umpteen different kinds of terminals and configurations and curses knows them all. You can even do text windows. Still, it is "easier" than interacting with the terminal, but only because the terminal is so cryptic.
Tron55555 wrote:
P.S. -- on a separate note, can anyone tell me, when formatting a quote on these forums, how I can write who's quote is it? When the quote says, for example, "etresoft wrote..." -- how do I do that? I checked the Help section under How to Format Text, but it didn't have anything about quotes. Thanks.
etresoft wrote:
Just hit the "quotes" button and see how the forum does it.
"Abraham Lincoln" wrote:
Four score and seven years ago...