input text file - use debugger?

[c_lady]

Hi guys!

Lets say I have the below program (K&R, 1.9), which simply does:

while (there's another line)
if (it's longer than the previous longest)
(save it)
(save its length)
print longest line

#include <stdio.h>
#define MAXLINE 1000 /* maximum input line length */
int getline(char line[], int maxline);
void copy(char to[], char from[]);
/* print the longest input line */
main()
{
	int len; /* current line length */
	int max; /* maximum length seen so far */
	char line[MAXLINE]; /* current input line */
	char longest[MAXLINE]; /* longest line saved here */
	max = 0;
	while ((len = getline(line, MAXLINE)) > 0)
		if (len > max) {
			max = len;
			copy(longest, line);
		}
	if (max > 0) /* there was a line */
		printf("%s", longest);
	return 0;
}
/* getline: read a line into s, return length */
int getline(char s[],int lim)
{
	int c, i;
	for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
		s[i] = c;
	if (c == '\n') {
		s[i] = c;
		++i;
	}
	s[i] = '\0';
	return i;
}
/* copy: copy 'from' into 'to'; assume to is big enough */
void copy(char to[], char from[])
{
	int i;
	i = 0;
	while ((to[i] = from[i]) != '\0')
		++i;
}

How I can give a text file, and use a debugger and see how it works? I want to understand somethings ... is that possible?

[whiteflags]

If you really want to make the program take input from a file, you shouldn't have to make any coding changes, just run something like

executable < test.txt

In IDEs setting that up is dead simple since there should be a place to change command line arguments somewhere in the project settings.

All you have to do is invoke your debugger when you are ready and step through the lines.

[c_lady]

All you have to do is invoke your debugger when you are ready and step through the lines.

How to invoke my debugger? I use xCode ... any suggestion?

[msh]

I want to understand somethings ... is that possible?

That would depend solely on you, wouldn't it?

I understand that Xcode comes with a debugger (I looked it up on Wikipedia), or rather a front-end for gdb. Try using that? There should be a "Debug" button or similar on the toolbar.

[c_lady]

I think this impossible! Since I need to debug (build) my program successfully before i give an input text etc. So how come my debugger will be involved when the program already has created successful object code... Lets hope some experience users to clarify this question... and disprove what msh and whiteflags had said!

[anduril462]

Let me google that for you.
And here's another freebie.

[iMalc]

I think this impossible! Since I need to debug (build) my program successfully before i give an input text etc. So how come my debugger will be involved when the program already has created successful object code... Lets hope some experience users to clarify this question... and disprove what msh and whiteflags had said!

Well it's a little hard to disprove the truth...

Debuggers typically make use of an additional symbol file (often with a .pdb extension or some such) to make sense of the already compiled file that you are executing when you debug things.

If there is no built exe first, then what you have is an interpreter, not a compiler, and I'm not sure if any of those exist for the C programming language.

[CommonTater]

I think this impossible! Since I need to debug (build) my program successfully before i give an input text etc. So how come my debugger will be involved when the program already has created successful object code... Lets hope some experience users to clarify this question... and disprove what msh and whiteflags had said!

First of all you have to compile it in "debug" mode with debugging symbols imbedded into the resulting obj and exe files... Then the debugger just follows what the program is doing...

It's done all the time.