Design... the right way.

[mike.rosset+gnus@gmail.com]

Hello All:


I am new to C and I have a program design question. Not only am I trying
to learn C but I'm also trying to pick up good habits. And I'm cocerned
with doing things the right and avoiding picking up bad habits.

The program I'm working on uses popen to read some pre-formatted output
from another program. The output looks like this.

line 0: persons_name
line 1: persons_last_na me
line 2: .....

I then need to take each line assign it to a structure member. What
would be the simplest approach to find the member field from the line
loop count?

Michael Rosset

[Richard Heathfield]

Re: Design... the right way.

mike.rosset+gnu s@gmail.com said:

>
Hello All:
>
>
I am new to C and I have a program design question. Not only am I trying
to learn C but I'm also trying to pick up good habits. And I'm cocerned
with doing things the right and avoiding picking up bad habits.
>
The program I'm working on uses popen to read some pre-formatted output
from another program. The output looks like this.
>
line 0: persons_name
line 1: persons_last_na me
line 2: .....
>
I then need to take each line assign it to a structure member. What
would be the simplest approach to find the member field from the line
loop count?

Given these rules:
1) you have at least one whole line in memory on each iteration of the loop
2) there is a colon in every line
3) the colon precedes the member field
4) there is nothing but whitespace between the colon and the member field
5) the member field contains no whitespace

you can get the member field like this:

char *fieldend = NULL;
char *colon = strchr(line, ':');
char *fieldstart = colon + 1;
while(isspace(( unsigned char)*fieldstar t))
{
++fieldstart;
}
fieldend = fieldstart + 1;
while(*fieldend != '\0' && !isspace((unsig ned char)*fieldend) )
{
++fieldend;
}

fieldend now points one byte beyond the member field. You can print the
exact contents of the member field like this:

printf("Field contents = [%.*s]\n", fieldend - fieldstart, fieldstart);

or, given at least 1 + fieldend - fieldstart bytes, you can make a string
out of it like this:

memcpy(target, fieldstart, fieldend - fieldstart);
target[fieldend - fieldstart] = '\0';

If that solves your problem, great. If it only moves you a bit closer to
it, what more do you need?

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Nick Keighley]

Re: Design... the right way.

On 26 Jun, 04:03, mike.rosset+g.. .@gmail.com wrote:

I am new to C and I have a program design question. Not only am I trying
to learn C but I'm also trying to pick up good habits.

good
:-)

And I'm cocerned
with doing things the right [way] and avoiding picking up bad habits.
>
The program I'm working on uses popen

popen() isn't actually standard C. It's standard Unix (Posix).
But your question becomes a standard C question if we assume you're
reading
from a stream (eg. opened by fopen())

to read some pre-formatted output
from another program. The output looks like this.

that is the *input* to your program looks like:

line 0: persons_name
line 1: persons_last_na me
line 2: .....
>
I then need to take each line assign it to a structure member. What
would be the simplest approach to find the member field from the line
loop count?

I'm not sure. What are the structure members called?
When I read your question I thought persons_name
indicated a name and the actual input looked like

line 0: frodo
line 1: baggins

etc.

So you might be doing something like

void process_lines (struct Record *record)
{
char line [LARGEST_LINE];
char field [LARGEST_FIELD];
int line_count = 0;

while (read_line(line ) == OK)
{
line_count++;
get_field (field, line);

switch (line_count)
{
1:
strcpy (record->person_name, field);
break;

2:
strcpy (record->persons_last_n ame, field);
break;

default:
fprintf (stderr, "Dire Straits!\n");
exit (EXIT_FAILURE);
}
}
}

which isn't exactly elegant...
The error handling is weak, the program is very trusting of the input
source.

I'd do get_field() more like this (a different approach to
RH's solution).

int get_field (char *field, const char *line)
{
int line_count
if (sscanf (line, "line %d: %s", &line_count, field) != 2)
return PARSE_ERROR;

return OK;
}

Could you explain your problem in more detail?


--
Nick Keighley

/*
- Note:
- I wanted to put a check in getGuiExtract() , but it's a void
method, inherited from the father of the father of the father of
the
[...]
the father of the father of the father of the father of the
father ...

So I can't modify its interface.
*/
[cry for help found in source code]

[mike.rosset+gnus@gmail.com]

Re: Design... the right way.

pete <pfiland@mindsp ring.comwrites:

>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
>
#define MAX_FIELDS 19
#define PATH_MAX 10
>
enum pkg_vars {
pkgname,
pkgver
};
>
int main(void)
/*
** non prototype declarations
** is an obsolescent feature of the language
*/
{
int lines = 0;
char package[MAX_FIELDS][PATH_MAX];
/*
** A two dimensional array of char
*/
FILE *input = fopen("./test.sh", "r");
char line[PATH_MAX + 1];
>
if(input == NULL) {
perror("Error: running parser");
/*
** Nothing to fclose here
*/
exit(EXIT_FAILU RE);
}
while(fgets(lin e, PATH_MAX, input)) {
line[strlen(line) - 1 ] = '\0';
if(lines < MAX_FIELDS) {
strcpy(package[lines], line);
}
lines++;
}
printf("name = %s\n", package[pkgname]);
printf("pkgver = %s\n", package[pkgver]);
printf("total = %d\n", lines);
/*
** A portable text stream, ends in a newline character.
*/
fclose(input);
return 0;
}

Pete, thanks for your response. Thank you for for your suggestions, all
of them make sense. I have a couple of questionsi. When you say "non
prototype declarations" you mean I should declare void as a parmater, it
not to be assumed.

Also I'm not sure what you mean by a portable stream should end in a
newline. Does that mean I should'nt remove it from line or I should copy
the line then remove it?

Mike Rosset

[Mike Wahler]

Re: Design... the right way.


<mike.rosset+gn us@gmail.comwro te in message
news:87ej6ki1l7 .fsf@gmail.com. ..

pete <pfiland@mindsp ring.comwrites:
>

>>
>#include <stdlib.h>
>#include <stdio.h>
>#include <string.h>
>>
>#define MAX_FIELDS 19
>#define PATH_MAX 10
>>
>enum pkg_vars {
>pkgname,
>pkgver
>};
>>
>int main(void)
>/*
>** non prototype declarations
>** is an obsolescent feature of the language
>*/
>{
>int lines = 0;
>char package[MAX_FIELDS][PATH_MAX];
>/*
>** A two dimensional array of char
>*/
>FILE *input = fopen("./test.sh", "r");
>char line[PATH_MAX + 1];
>>
>if(input == NULL) {
>perror("Erro r: running parser");
>/*
>** Nothing to fclose here
>*/
>exit(EXIT_FAIL URE);
>}
>while(fgets(li ne, PATH_MAX, input)) {
>line[strlen(line) - 1 ] = '\0';
>if(lines < MAX_FIELDS) {
>strcpy(packa ge[lines], line);
>}
>lines++;
>}
>printf("name = %s\n", package[pkgname]);
>printf("pkgv er = %s\n", package[pkgver]);
>printf("tota l = %d\n", lines);
>/*
>** A portable text stream, ends in a newline character.
>*/
>fclose(input );
>return 0;
>}

>
>
Pete, thanks for your response. Thank you for for your suggestions, all
of them make sense. I have a couple of questionsi. When you say "non
prototype declarations" you mean I should declare void as a parmater, it
not to be assumed.

int f(); /* declaration; does not specify parameters */
/* in C, an empty parameter list means 'not specified' */

int f(int a, char b); /* declaration; also a prototype (specifies
/* arguments)

int f(void); /* declaration/prototype: specific about arguments */
/* (in this case there are none */

>
Also I'm not sure what you mean by a portable stream should end in a
newline. Does that mean I should'nt remove it from line or I should copy
the line then remove it?

You can remove and put it back all you like, but what he's
saying is that the very last character in the stream should
be a newline ('\n').

-Mike

[David Thompson]

Re: Design... the right way.

On Thu, 26 Jun 2008 15:27:48 GMT, "Bartc" <bc@freeuk.comw rote:

>
<mike.rosset+gn us@gmail.comwro te in message
news:873an0i8ul .fsf@gmail.com. ..

The data format looks more like this

Frodo
Baggins
Hobbit

>
I vaguely remember Bilbo Baggins, so are these first names or last names?
>

<OT highly summarizedFrodo is indeed (fictionally) the first name of
Bilbo's honorary nephew and heir, who thus becomes the 'ring-bearer'
to take the One Ring to Mount Doom to be destroyed, through (nearly
all of) the _Lord of the Rings_ trilogy. I can imagine how you might
have ignored the books -- not forgive, just imagine <G-- but totally
missing three _huge_ Hollywood movies is quite an accomplishment. </>

/* popen? *waves hand* yes its fopen, continue on your way.*/
FILE *input = popen("./test.sh", "r");

>
I'm not familar with popen, from the docs it doesn't seem appropriate. Try
fopen().
>

OP previously said he wants this program to parse _the output of
running a script namely test.sh_ so it's very appropriate. But OT.
(But the issues of parsing and storing are mostly the same whether the
input comes from a running script or a plain file, and hence ontopic.
The only obvious exception would be if you wanted to rewind or
otherwise reposition in the input, which fails for a pipe; but then in
Standard C it may fail even for a 'real' file -- if any such.)

- formerly david.thompson1 || achar(64) || worldnet.att.ne t