Thread: unix fold utility

Hello again! lol. I have to create a fold utility program as our final project (we had 3 choices). I am having trouble getting started on it. I will post a link to the description of what the fold command is supposed to do.

http://www.conestogac.on.ca/~set/cou..._fold_2008.htm

This is due on Tuesday btw.

UPDATE: So far I have this...

Code:

#include <stdio.h>

int main(int argc, char *argv[])
{
	FILE *inputFile; //pointer to a file//

	if (argv[1] == '-s')
	{
	// Fold line after the last blank character within the first width column positions. 
	// If there is no such character, fold anyway. 
	}

	if (argv[2] == '-w' && argv[3] == /* width variable here*/)
	{
	// Specify a line width to use instead of the default 80 columns.
	}

	inputFile = fopen(argv[4], "r"); //open a file for reading//

	if (inputFile = fopen(argv[4], "r") == NULL)
	{
		printf("Cannot open file for reading.\n"); //display error if file is not found//
		return -1;
	}
	
	if (inputFile = fopen(argv[4], "r") != NULL)
	{
		return -2;
	}

	//other code here//

	return 0;
}

I guess that separate functions would be a good idea to use for each command line argument?

Can I ask if this is your major and you started in September?

And technically, the error message when you can not open the file is incorrect.

--
Mats

I believe this to be a foolproof and completely optimized way of parsing your particular options:

Code:

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

void wrong () {
	puts("Usage: fold [-s] [-w width] file ...");
	exit (-2);
}

int parse_w (char *arg) {
	int i, retv;
	if (sscanf(arg,"&#37;d",&retv)!=1) wrong();
	return retv;	
}

int main (int argc, char *argv[]) {
	int i, len, sflag=0, width=80;
	FILE *fstRO;
	for (i=1;i<argc;i++) {
		if (strcmp(argv[i],"-s")==0) {sflag=1;continue;}
		if (strncmp(argv[i],"-w",2)==0) {
			if (strlen(argv[i])>2) {
				if (sscanf(argv[i], "-w%d",&width)!=1) wrong();
				continue;}
			else if (i==argc-1) wrong();
			width=parse_w(argv[i+1]);
			i++; continue;
		}
		break;
	}
	if (!(fstRO=fopen(argv[i],"r"))) {
		puts("File not openable");
		return -1;}
	printf("%s opened read-only\n",argv[i]);
	if (sflag==1) puts("-s set");
	printf("width set to %d\n",width);
	fclose(fstRO);
	return 0;
}

edit: except it doesn't parse the filename...oh well
edit2: okay now it does

Originally Posted by tabstop

That looks like it should be right for the switches, if not the filenames, of course. I think the usual idiom is a switch on the second letter of the argument; for two possible arguments I don't know that there's a performance hit either way, but the switch may make it a little easier to tell "illegal option" from "first filename".

Our paths crossed, I edited it to get the filename. Re: what you are saying about optimization, so

Code:

 
if (argv[i][0]=='-') switch (argv[i][1]) {
            case ('s'):
   //...etc

I guess this could save some strcmp

Before handing over the assignment the teacher must have covered how to do option processing. Hard to believe she or he would just pull it out of the hat.