Thread: program printing ".N=?" at beginning of string

I've written a program to read a string from the UNIX command line, and repeat or reverse it depending on the command line options it's given, and it seems to be working correctly apart from for some reason printing ".N=?" (without quotes, and question mark in a bold hexagon) at the beginning of my string.

here is my code:

Code:

#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main(int argc, char *argv[]) {	

char option;				
char string[100];			//To store string being processed
char rstring[100];			//To store reverse string

int n,i;				//n for number of repeats, i for iteration of loop
opterr=0;				//Disable standard error messages 

while((option=getopt(argc,argv,"hr:b"))!=-1){
	printf("string=%s\n",string);	
	i=1;							//skip parsing of program name	
	while(i<argc){						//parse through strings 
		if(!strcmp(argv[i],"-r")){ 			//if r option found...
			i+=2;					//... skip option and argument
		}else{
			if(!strcmp(argv[i],"-b")){		//if b option found...
				i++;				//...skip option
			}else{
				strcat(string,argv[i]);		//otherwise, add current string to string
				strcat(string," ");		//add space between words of string		
				i++;				//increment counter, move to next string		
			}
		}
	}	

/*then I have a switch statement to take the command line options and perform the 
functions on the string, which I know work as I've tested seperately. 
The printfs above are for debugging.

This part of the code is just for reading the string from the command line (ignoring any options there may be), but for some reason it puts the ".N=?" at the beginning of the string. This happens even with the first printf before the nested if statements.

Anyone know whats wrong?

It's kind of awkward to use getopt and then also try to get a parameter from the command line yourself. Why don't you just use getopt to get the string (so myprog -s "blah blah" -r or whatever) and then proceed from there?

Code:

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

int main(int argc, char *argv[]) {
	int opt;
	char *string;
	if (argc<2) return 0;
	while ((opt=getopt(argc,argv,"s:"))>0) switch(opt) { 
		case ('?'): puts("error"); return 0;
		case ('s'): string=malloc(strlen(optarg)+1);
			strcpy(string,optarg); break;
		default: break;
	}
	puts(string); free(string);	
	return 0;
}

Originally Posted by bertazoid

I thought this might be the case, but thing is, i need an empty string to begin with, since I'm concatenating each word of the command line to the string.

One thing you can do to have an "empty" string prepped for strcat is:

Code:

char string[256]="\0";

This means string has a strlen of 0, and (string[0]=='\0') will be true. It won't contain any initial garbage for printf either.
'\0' is the NULL TERMINATOR.

Originally Posted by bertazoid

mk27, I'm not familiar with the malloc function you've used, I haven't got that far yet in my course. Also, I'm trying to read in anything following the options, but not the options, option arguments, or program names themselves. and the options could appear in any order, or may be completely absent.

I might try using the memset function. I'm assuming i just use memset(string);

Okay, don't use malloc. Just use "char string[whatever size]" (and omit free()). But do believe what I am trying to say about getopt. It will make everything much simpler UNLESS the prof said specifically you cannot use "-s blah" to input the string. It doesn't matter to getopt what order the options are in either.

Regarding memset(), read post #8 first.