Thread: Alternative console output functions to printf()?

I'm trying to write a simple CL program that prints a line of text and repeats that line of text every time you press a key unless 'q' is pressed., at which point the program terminates.

Easy, right? Sure. Took me about 3 minutes. Here's the problem:

I'm using it as a listener program for netcat. I want my guys to be able to use this to debug port forwarding problems, etc.. The netcat tutorial says to use cmd.exe as a listener. It works great, but it's a huge security hole.

The problem with my simple CL utility is that the output from printf() or puts() doesn't redirect the way I/O from cmd.exe, or ipconfig.exe does. It doesn't show up on the calling client's screen.

Some MS utilities have redirectable output, some don't.

Which output functions should I use to make this work?

Thanks in advance ..

Correct. Any utility using stdout can have the output piped to somewhere else. However, when using a listener program for netcat, stdout and stdin obviously aren't what's being redirected.

I want to know what cmd.exe, ipconfig.exe, and nslookup ARE using for I/O. It is obviously not stdin/stdout.

Originally Posted by stahta01

How To Ask Questions The Smart Way

Why did you NOT link to the tutorial?
Why did you NOT post this in Windows or Networking sub-forum?

Tim S.

If you have no further suggestions, I understand. There is no need to try to derail the subject.

This is about existing alternatives to standard I/O.

These aren't win32 processes. This is a DOS command line utility. The fact that it is on a windows PC is irrelevant. The exact same thing happens when compiling and running it on linux. STDOUT does not redirect.

The difference is that on linux I can write a shell script that works. Not so on a MS machine.

Originally Posted by Codeplug

Some concrete examples that other can play with and examine might help.

gg

Sure. I think I figured part of it out though. For the output I had to use putc(stdout) and then fflush(stdout)

Code:

/*
 * Simple listener program for use with NetCat
 *  
 */
#include <stdlib.h>
#include <stdio.h>


void PutStr(char *str)
{
	int i;
	for(i=0; str[i]!='\0'; i++) 
	{
		putc((int)str[i], stdout);
	}
	fflush(stdout);
}
int main(int ac, char **av)
{
    int ch, Counter=1, PortNum=atoi(av[1]);
    char str[80];


    sprintf(str, "\n\n\tRunning .........\n\n");
    PutStr(str);    


    do{        
	sprintf(str, "\t\tYes, I am listening on port %d. [%d]\n", PortNum,Counter++);
        PutStr(str);
	ch=getchar();
		
    }while(ch!='q');


    return 0;
}

it is called like: >listener 4545

it works the same on DOS or linux.

Now I need to figure out how to get single character input without the user having to press <Enter> after each keypress ...

Oh! You were talking about unbuffered IO. Since you're only calling fflush after you putc the entire string, you might as well just call printf/fprintf then call fflush. Also, you can look into the setvbuf function to make stdout unbuffered.

Note that using setvbuf to unbuffer stdin will not fix the needing to press <enter> after each keypress. For that, you should look here: FAQ > How can I get input without having the user hit [Enter]? - Cprogramming.com.

Originally Posted by stahta01

WHY DID YOU NOT LINK TO TUTORIAL?

Tim S.

It's on the boat and the boat isn't connected to shore power so I am unable to link. If it's really important to you I can send someone out in a dinghy.

I hope this helps.