clearing the buffer??

**shuuhen** · 11-23-2007

Originally Posted by ssharish2005

call this function instead of fflush(stdin)

Code:

void clear_buffer(void)
{
     int ch;
     
     while((ch = getchar()) != '\n' && ch != EOF);
}

If you would have searched, i might have written this code around 1000 times lol

ssharish

How's that needed in alexnb185's code? Wouldn't that just make the user press return or ctrl-D (or if they have a more interesting way of sending EOF...) before typing the name of the app? Reading into a large buffer with fgets() should virtually avoid the "flushing the buffer" problem. The buffer doesn't seem to be a problem in this case. The problem is the newline being read in by fgets(), which the couple of lines below the comment in the article I specified should take care of.

**ssharish2005** · 11-23-2007

Well OK if that was the case use a strchr to get elimiated witht he '\n' char. And perhaps the reason why i posted that code was that i saw a fflush(stdin) call on the code. And hence i posted the code.

And if the '\n' was the main thing bothering you try replaced them with the '\0' char.

ssharish

**alexnb185** · 11-24-2007

well no I can't type anything at all.. it just puts in .app for me.. I am not sure if you understand that.. maybe you do.. maybe I am just a moron and don't understand you.. idk...

**Salem** · 11-24-2007

> printf("Type in the name of the app\n");
> fflush(stdin);
> fgets(applic, 15, stdin);
> sprintf(applic2, "\"%s\"", applic);
1. Remove ALL your fflush(stdin), it's undefined, and on any unix system it does nothing (at best) on an input stream.
2. Use fgets() with a large temporary buffer, not a short final result.
3. In this instance, you'll be wanting to remove the newline from the end of the line, which fgets stores.

Code:

char buff[BUFSIZ];
printf("Type in the name of the app\n");
fgets(buff, sizeof buff, stdin);

{ char *p = strchr(buff,'\n'); if ( p ) *p = '\0'; } /* delete the newline, if present */

strncpy( applic, buff, sizeof applic );              /* safe copy of user input */
applic[sizeof applic - 1] = '\0';                    /* make sure it's a valid string */

sprintf(applic2, "\"%s\"", applic);

But you could do the whole thing in one call, say

Code:

sprintf( empty2, "open -a \"%s\".app", applic );

But shouldn't the .app be inside the double quotes?

**Dino** · 11-24-2007

Originally Posted by alexnb185

well no I can't type anything at all.. it just puts in .app for me.. I am not sure if you understand that.. maybe you do.. maybe I am just a moron and don't understand you.. idk...

It's very understandable. Here's what they have been trying to tell you.

The problem is not that the newline is left in stdin at all. fgets() reads the user's string, AND the newline sequence and places both in your buffer. (applic).

With subsequent sprintfs(), you are carrying the newline sequence to subsequent buffers. Finally, when you issue the "open" command to system(), you are passing the newline sequence in the middle of your command, like this:

open -a "Photo Booth\r\n".app

To fix this, when you read the user's application name AND their newline, you need to remove the newline sequence from the end of the string. An easy way to do this is with strtok():

Code:

	printf("Type in the name of the app\n");
	fgets(applic, 15, stdin);  // read user's string, including the newline 
	sprintf(applic2, "\"&#37;s\"", strtok(applic, "\r\n") );  // truncate user's string just before the newline sequence
	sprintf(empty1, "open -a %s", applic2);
	sprintf(empty2, "%s.app", empty1);

Using both the carriage return (\r) and line feed (\n) as tokens, you will grab whichever one comes first in the string. (On a Mac, the \r).

Todd

**alexnb185** · 11-24-2007

Todd! thank you so much! That makes perfect sense now! Really, thank you.

**alexnb185** · 11-24-2007

Well, that still didn't fix it, it happened again, only it put a (Null) before the usual app

heres the output in the console:

This program can open applications or delete files
Please select what you like to do
enter 'Delete' to delete files, or 'open' to open
o
Type in the name of the app
Unable to find application named '(null).app'
new-host:C programs Alex$

**Dino** · 11-24-2007

Don't put quotes around the .app, just around the application name. It absolutely works for me.

Todd

**alexnb185** · 11-24-2007

I didn't, I have it with the quotes only around the name of the application, or exactly what the user types in... heres the code:

Code:

printf("Type in the name of the app\n");
			
			
			fgets(applic, 15, stdin);
			
			sprintf(applic2, "\"&#37;s\"", strtok(applic, "\r\n") );
	
			sprintf(empty1, "open -a %s", applic2);
	
			sprintf(empty2, "%s.app", empty1);
	
			system(empty2);

**shuuhen** · 11-24-2007

strtok() returns a pointer to a string, not the string itself. I recommend going over Salem's post. If you can use and understand the code in that post, you will have fewer problems with future input (it uses good programming practices, like safely copying strings).

**Salem** · 11-24-2007

> sprintf(applic2, "\"%s\"", strtok(applic, "\r\n") );
1. Unless you open a file in binary mode (unusual for a text file, less so for stdin), then the only termination character in the buffer will be \n.

2. If the user decides to type in too much data, then there will be NO newline in the input and strtok() will return NULL. Which probably explains where the (null) was coming from in the following test by alexnb185.

A buffer of 15 chars will only get you 13 chars of useful input, a newline and a \0.
This is why I suggest a large buffer + some careful validation to being with.

**alexnb185** · 11-24-2007

ok well Salem I tryed what you said in the post right above me, but it still does it :[ the same (NULL).app thing... this is of course without me typing anything at all

**alexnb185** · 11-24-2007

OK, this is getting to be quite the little project lol... but Salem I did what you said to do in the earlier post as well, it did eliminate the (NULL), however the .app is still there in the console, so, still dealing with that... heres the code:

Code:

char empty1[40];
			char empty2[65];
			char applic[25];
			char applic2[28];
			char buff[BUFSIZ];
				printf("Type in the name of the app\n");
				fgets(buff, sizeof buff, stdin);

				{ char *p = strchr(buff,'\n'); if ( p ) *p = '\0'; } /* delete the newline, if present */

				strncpy( applic, buff, sizeof applic ); 			/* safe copy of user input */
				
					applic[sizeof applic - 1] = '\0'; 
					
			sprintf(applic2, "\"&#37;s\"", applic);
	
			sprintf(empty1, "open -a %s", applic2);
			
			sprintf(empty2, "%s.app", empty1);
	
			system(empty2);

**Salem** · 11-24-2007

So do something like
printf( "Command=%s\n", empty2 );
and see what it prints.

From what I can make out, you end up with
open -a "user input".app

My guess is the .app needs to be inside the double quotes along with the rest of your input.

**Dino** · 11-24-2007

Perhaps the problem you are having is that there is already a newline in the buffer prior to this function being called. With this small snippet of code, it works perfectly for me. I entered Finder and Finder was opened.

Todd