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Re: [help-gengetopt] show help if no input

From: Lorenzo Bettini
Subject: Re: [help-gengetopt] show help if no input
Date: Wed, 18 Aug 2010 20:35:06 +0200
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On 08/18/2010 04:26 PM, Duke wrote:
On 8/18/10 5:42 AM, Lorenzo Bettini wrote:
On 17/08/2010 22.15, Duke wrote:
Hi folks,

Hi there

Hi Lorenzo,

I just heard about gengetopt, tried it and like it very much. I want
to change the default reaction of gengetopt a little bit to suit my
purpose better, so I have two questions below:

* When Print help, is there a way showing that one option is optional
and the other is required? For now, help shows only options and their
descriptions and values, no way to know if an option is optional or
required until one tries the program and some of its options.

for the moment this is not implemented, although in the summary of
command invocation optional options should be printed differently (I
should check this, I don't remember it right now and cannot check it

I am new to gengetopt, so I am not quite sure what you mentioned. What
is the "summary of command invocation"? Is it printed when "-h" is used,
or one has to use another option?

when you use -h|--help, but you must have generated the command line parser with

 -l, --long-help               long usage line in help

(this is an option to be passed to gengetopt)

then, when print the output of help you'll have something similar

Usage: sample1 -iINT|--int-opt=INT [-h|--help] [--detailed-help] [--full-help] [-V|--version] [-sfilename|--str-opt=filename] [-mINT|--my-opt=INT] [--flag-opt] [-F|--funct-opt] [--long-opt=LONG] [--def-opt=STRING]
              [--enum-opt=STRING] [-DINT|--dependant=INT] [FILES]...

Surely, this behavior could be added (by using a command line switch
of gengetopt itself); I should work on this (or if you want to try to
implement it...)

Well, it is quite beyond my ability now. I am just a learner in C/C++.
But I am willing to assist if possible.

by the way, I've just realized there's already something for this (see also the manual):

if --show-required is given, possibly with a string, in the output of --help will be made explicit which options are actually required,

* When there is no input (no argument or argc < 2), is there a way of
telling gengetopt to show help, even if there are required options?
For now, if there is required option, and if the program is invoked
without argument, then "option required" shows up, not the help.

this could be implemented in your program itself; as long as you init
an args_info structure, then you could check argc and in case call the
print help generated function directly; have you tried this?

I might have missed something/some options, but here is what I tried:

gengetopt_args_info args_info;
if ( cmdline_parser (argc, argv, &args_info) != 0 ) {
return 1;

string Input;
if ( argc >= 2 && args_info.inputs_num == 1 ) {
Input = args_info.inputs[0];
} else {
if ( argc < 2 ) {
return usage( args_info, false );
} else if ( args_info.help_given ) {
return usage( args_info, true );
} else if ( args_info.inputs_num == 0 ) {
cerr << "No input file. Program aborts!" << endl;
} else if ( args_info.inputs_num > 1 ) {
cerr << "Too many input files. Program aborts!" << endl;
return ProgramExit(args_info);


int ProgramExit( gengetopt_args_info args_info ) {
cmdline_parser_free (&args_info);
return -1;

So basically when there is no input (no argument, or argc < 2), help
should be printed. This works only if I do not have any required option.
If there is one required option, "option required" notification will
show up. I think the condition to show "option required" is not just
args_info.(some_option)_given, but also argc >= 2 in this situation.
What do you think?

I meant something different: before invoking

cmdline_parser (argc, argv, &args_info) != 0

you could do something similar (not checked it myself)

if (argc < 2) {
cmdline_parser_init (&args_info);
return -1;

does this do what you need?

please, let me know

Lorenzo Bettini, PhD in Computer Science, DI, Univ. Torino
ICQ# lbetto, 16080134     (GNU/Linux User # 158233)

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