Thread: Need help debugging this simple yet elusive problem

  1. #1
    Registered User
    Join Date
    Oct 2008

    Need help debugging this simple yet elusive problem

    Simple scanning in an input with whitespaces except I can't figure out why the code is enter my 'if' statement when i don't input anything. Can anyone see the problem?


       while(exitStatus != 0){
    	printf("Say(0 to exit): ");
    	//scanf("%s", &message);  
    	int inc = 0;
    	   while((ch = getchar()) != '\n')
    	   	message[inc++] = ch;}	
    	   message[inc] = '\0';
    	   inc = 0;
    	while(message[inc] != '\0'){
    	if(strcmp(message, "0") == 0){
    		exitStatus = 0;
    		printf("Exiting", exitStatus);
    	char *ptr = message;
    	printf("Sent '%s' to server.\n",message);
    and the output is:

    Say(0 to exit):
    Sent '' to server.
    Say(0 to exit):
    I don't know where the " '' " is coming from since nothing is getting passed in. Thanks.

  2. #2
    Registered User
    Join Date
    Oct 2008
    so somehow there is a '\n' getting passed in but i don't know where :\

  3. #3
    Registered User slingerland3g's Avatar
    Join Date
    Jan 2008
    First thought I have is you should initialize your array to some default data, say all 1's. I say this since you are searching for "0" to compare against to exit.

  4. #4
    Make Fortran great again
    Join Date
    Sep 2009
    I assume that you have a scanf right before you hit this bit of code? It's a common problem with back to back scanfs. You might want to look up "clearing the stdin buffer". Remember to not use fflush(stdin), as this is undefined.

  5. #5
    Registered User
    Join Date
    Oct 2008
    well I am using a scanf earlier in my code, but I am not using a scanf in this portion as I have it commented out. If I uncomment the scanf it works fine but will not permit the use of white spaces. Unless there is some correlation between the scanf used earlier and the getchar() function.

  6. #6
    Registered User
    Join Date
    Sep 2006
    scanf() can leave a newline char in the keyboard buffer, and muck up the next part of your program that gets data from the keyboard.

    You can pull the troublesome newline char off the buffer by adding a variable=getchar() line of code, right after the scanf().

    If your program stops, awaiting your keyboard input, then you don't have a newline waiting in the buffer. If it continues on, then 1 char (probably the newline), will have been pulled off the buffer.

    If your scanf()'s are only for numbers, then it's no problem, and you can ignore this. When scanning for digits, scanf() will skip over newlines, anyway. Char's are the usual problems, because a newline char is a char itself. scanf() won't skip over a newline if it's expecting a char.

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