aboutsummaryrefslogtreecommitdiff
path: root/README.md
blob: da4b9d79767a2114a850c55621ea39882f321263 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
# args

[![build status](https://gitgud.io/Taywee/args/badges/master/build.svg)](https://gitgud.io/Taywee/args/commits/master)

A simple, small, flexible, single-header C++11 argument parsing library, in
about 1K lines of code.

This is designed to somewhat replicate the behavior of Python's argparse, but
in C++, with static type checking, and hopefully a lot faster.

UTF-8 support is limited at best.  No normalization is performed, so non-ascii
characters are very best kept out of flags, and combined glyphs are probably
going to mess up help output if you use it.  Most UTF-8 necessary for
internationalization should work for most cases, though heavily combinatory UTF
alphabets may wreak havoc.

This program is MIT-licensed, so you can use the header as-is with no
restrictions. I'd appreciate attribution in a README, Man page, or something if
you are feeling generous, but all that's required is that you don't remove the
license and my name from the header of the args.hxx file in source
redistributions (ie. don't pretend that you wrote it).  I do welcome additions
and updates wherever you feel like contributing code.

The API documentation can be found at https://taywee.github.io/args

The code can be downloaded at https://github.com/Taywee/args

There are also somewhat extensive examples below.

# What does it do?

It:

* lets you handle flags, flag+arguments, and positional arguments simply and
    elegently, with the full help of static typechecking.
* allows you to use your own types in a pretty simple way.
* lets you use count flags, and lists of all argument-accepting types.
* Allows full validation of groups of required arguments, though output isn't
    pretty when something fails group validation.  User validation functions are
    accepted.  Groups are fully nestable.
* Generates pretty help for you, with some good tweakable parameters.
* Lets you customize all prefixes and most separators, allowing you to create
    an infinite number of different argument syntaxes
* Lets you parse, by default, any type that has a stream extractor operator for
  it.  If this doesn't work for your uses, you can supply a function and parse
  the string yourself if you like.
* Lets you decide not to allow separate-argument argument flags or joined ones
  (like disallowing `--foo bar`, requiring `--foo=bar`, or the inverse, or the
  same for short options).

# What does it not do?

There are tons of things this library does not do!


## It will not ever:

* Allow you to create subparsers like argparse in a master parser (you can do
    this yourself with iterators and multiple parsers)
* Allow one argument flag to take a specific number of arguments
    (like `--foo first second`).  You can instead split that with a flag list
    (`--foo first --foo second`) or a custom type extraction
    (`--foo first,second`)
* Allow you to intermix multiple different prefix types (eg. `++foo` and
    `--foo` in the same parser), though shortopt and longopt prefixes can be
    different.
* Allow you to have argument flags only optionally accept arguments
* Allow you to make flag arguments sensitive to order (like gnu find), or make
  them sensitive to relative ordering with positional flags.  The only
  orderings that are order-sensitive are:
    * Positional options relative to one-another
    * List positional options or flag arguments to each of their own respective
      items
* Allow you to use a positional argument list before any other positional
    arguments (the last argument list will slurp all subsequent positional
    arguments).  The logic for allowing this would be a lot more code than I'd
    like, and would make static checking much more difficult, requiring us to
    sort std::string arguments and pair them to positional arguments before
    assigning them, rather than what we currently do, which is assiging them as
    we go for better simplicity and speed.

# How do I install it?

```shell
sudo make install
```

Or, to install it somewhere special (default is `/usr/local`):

```shell
sudo make install DESTDIR=/opt/mydir
```

You can also copy the file into your source tree, if you want to be absolutely
sure you keep a stable API between projects.

## I also want man pages.

```shell
sudo make installman
```

This requires Doxygen

# How do I use it?

Create an ArgumentParser, modify its attributes to fit your needs, add
arguments through regular argument objects (or create your own), and match them
with an args::Matcher object (check its construction details in the doxygen
documentation.

Then you can either call it with args::ArgumentParser::ParseCLI for the full
command line with program name, or args::ArgumentParser::ParseArgs with
just the arguments to be parsed.  The argument and group variables can then be
interpreted as a boolean to see if they've been matched, and their arguments
can be pulled from their value and values attributes, if applicable.

# How fast is it?

This should not really be a question you ask when you are looking for an
argument-parsing library, but every test I've done shows args as being about
65% faster than TCLAP and 220% faster than boost::program_options.

The simplest benchmark I threw together is the following one, which parses the
command line `-i 7 -c a 2.7 --char b 8.4 -c c 8.8 --char d` with a parser that
parses -i as an int, -c as a list of chars, and the positional parameters as a
list of doubles (the command line was originally much more complex, but TCLAP's
limitations made me trim it down so I could use a common command line across
all libraries.  I also have to copy in the arguments list with every run,
because TCLAP permutes its argument list as it runs (and comparison would have
been unfair without comparing all about equally), but that surprisingly didn't
affect much.  Also tested is pulling the arguments out, but that was fast
compared to parsing, as would be expected.

### The run:

```shell
% g++ -obench bench.cxx -O2 -std=c++11 -lboost_program_options
% ./bench
args seconds to run: 0.895472
tclap seconds to run: 1.45001
boost::program_options seconds to run: 1.98972
%
```

### The benchmark:

```cpp
#undef NDEBUG
#include <iostream>
#include <chrono>
#include <cassert>
#include "args.hxx"
#include <tclap/CmdLine.h>
#include <boost/program_options.hpp>
namespace po = boost::program_options;
using namespace std::chrono;
inline bool doubleequals(const double a, const double b)
{
    static const double delta = 0.0001;
    const double diff = a - b;
    return diff < delta && diff > -delta;
}
int main()
{
    const std::vector<std::string> carguments({"-i", "7", "-c", "a", "2.7", "--char", "b", "8.4", "-c", "c", "8.8", "--char", "d"});
    const std::vector<std::string> pcarguments({"progname", "-i", "7", "-c", "a", "2.7", "--char", "b", "8.4", "-c", "c", "8.8", "--char", "d"});
    // args
    {
        high_resolution_clock::time_point start = high_resolution_clock::now();
        for (unsigned int x = 0; x < 100000; ++x)
        {
            std::vector<std::string> arguments(carguments);
            args::ArgumentParser parser("This is a test program.", "This goes after the options.");
            args::ArgFlag<int> integer(parser, "integer", "The integer flag", args::Matcher{'i', "int"});
            args::ArgFlagList<char> characters(parser, "characters", "The character flag", args::Matcher{'c', "char"});
            args::PosArgList<double> numbers(parser, "numbers", "The numbers position list");
            parser.ParseArgs(arguments);
            const int i = integer.value;
            const std::vector<char> c(characters.values);
            const std::vector<double> n(numbers.values);
            assert(i == 7);
            assert(c[0] == 'a');
            assert(c[1] == 'b');
            assert(c[2] == 'c');
            assert(c[3] == 'd');
            assert(doubleequals(n[0], 2.7));
            assert(doubleequals(n[1], 8.4));
            assert(doubleequals(n[2], 8.8));
        }
        high_resolution_clock::duration runtime = high_resolution_clock::now() - start;
        std::cout << "args seconds to run: " << duration_cast<duration<double>>(runtime).count() << std::endl;
    }
    // tclap
    {
        high_resolution_clock::time_point start = high_resolution_clock::now();
        for (unsigned int x = 0; x < 100000; ++x)
        {
            std::vector<std::string> arguments(pcarguments);
            TCLAP::CmdLine cmd("Command description message", ' ', "0.9");
            TCLAP::ValueArg<int> integer("i", "int", "The integer flag", false, 0, "integer", cmd);
            TCLAP::MultiArg<char> characters("c", "char", "The character flag", false, "characters", cmd);
            TCLAP::UnlabeledMultiArg<double> numbers("numbers", "The numbers position list", false, "foo", cmd, false);
            cmd.parse(arguments);
            const int i = integer.getValue();
            const std::vector<char> c(characters.getValue());
            const std::vector<double> n(numbers.getValue());
            assert(i == 7);
            assert(c[0] == 'a');
            assert(c[1] == 'b');
            assert(c[2] == 'c');
            assert(c[3] == 'd');
            assert(doubleequals(n[0], 2.7));
            assert(doubleequals(n[1], 8.4));
            assert(doubleequals(n[2], 8.8));
        }
        high_resolution_clock::duration runtime = high_resolution_clock::now() - start;
        std::cout << "tclap seconds to run: " << duration_cast<duration<double>>(runtime).count() << std::endl;
    }
    // boost::program_options
    {
        high_resolution_clock::time_point start = high_resolution_clock::now();
        for (unsigned int x = 0; x < 100000; ++x)
        {
            std::vector<std::string> arguments(carguments);
            po::options_description desc("This is a test program.");
            desc.add_options()
                ("int,i", po::value<int>(), "The integer flag")
                ("char,c", po::value<std::vector<char>>(), "The character flag")
                ("numbers", po::value<std::vector<double>>(), "The numbers flag");
            po::positional_options_description p;
            p.add("numbers", -1);
            po::variables_map vm;
            po::store(po::command_line_parser(carguments).options(desc).positional(p).run(), vm);
            const int i = vm["int"].as<int>();
            const std::vector<char> c(vm["char"].as<std::vector<char>>());
            const std::vector<double> n(vm["numbers"].as<std::vector<double>>());
            assert(i == 7);
            assert(c[0] == 'a');
            assert(c[1] == 'b');
            assert(c[2] == 'c');
            assert(c[3] == 'd');
            assert(doubleequals(n[0], 2.7));
            assert(doubleequals(n[1], 8.4));
            assert(doubleequals(n[2], 8.8));
        }
        high_resolution_clock::duration runtime = high_resolution_clock::now() - start;
        std::cout << "boost::program_options seconds to run: " << duration_cast<duration<double>>(runtime).count() << std::endl;
    }
    return 0;
}
```

So, on top of being more flexible, smaller, and easier to read, it is faster
than the most common alternatives.

# Is it developed with regression tests?

Yes.  tests.cxx in the git repository has a set of standard tests (which are
still relatively small in number, but I would welcome some expansion here), and
thanks to GitLab's CI, these tests run with every single push:

```shell
% make runtests
g++ test.cxx -o test.o -I. -std=c++11 -O2 -c -MMD
g++ -o test test.o -std=c++11 -O2
./test
===============================================================================
All tests passed (74 assertions in 15 test cases)

%
```

The testing library used is [Catch](https://github.com/philsquared/Catch).

# Examples

All the code examples here will be complete code examples, with some output.

## Simple example:

```cpp
#include <iostream>
#include <args.hxx>
int main(int argc, char **argv)
{
    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
    args::HelpFlag help(parser, "help", "Display this help menu", args::Matcher{'h', "help"});
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    return 0;
}
```

```shell
 % ./test
 % ./test -h
  ./test {OPTIONS} 

    This is a test program. 

  OPTIONS:

      -h, --help         Display this help menu 

    This goes after the options. 
 % 
```

## Boolean flags, special group types, different matcher construction:

```cpp
#include <iostream>
#include <args.hxx>
int main(int argc, char **argv)
{
    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
    args::Group group(parser, "This group is all exclusive:", args::Group::Validators::Xor);
    args::Flag foo(group, "foo", "The foo flag", args::Matcher{'f', "foo"});
    args::Flag bar(group, "bar", "The bar flag", args::Matcher({'b'}));
    args::Flag baz(group, "baz", "The baz flag", args::Matcher({"baz"}));
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    catch (args::ValidationError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    if (foo) { std::cout << "foo" << std::endl; }
    if (bar) { std::cout << "bar" << std::endl; }
    if (baz) { std::cout << "baz" << std::endl; }
    return 0;
}
```

```shell
 % ./test   
Group validation failed somewhere!
  ./test {OPTIONS} 

    This is a test program. 

  OPTIONS:

                         This group is all exclusive:
        -f, --foo          The foo flag 
        -b                 The bar flag 
        --baz              The baz flag 

    This goes after the options. 
 % ./test -f
foo
 % ./test --foo
foo
 % ./test --foo -f
foo
 % ./test -b      
bar
 % ./test --baz
baz
 % ./test --baz -f
Group validation failed somewhere!
  ./test {OPTIONS} 

    This is a test program. 
...
 % ./test --baz -fb
Group validation failed somewhere!
  ./test {OPTIONS} 
...
 % 
```

## Argument flags, Positional arguments, lists

```cpp
#include <iostream>
#include <args.hxx>
int main(int argc, char **argv)
{
    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
    args::HelpFlag help(parser, "help", "Display this help menu", args::Matcher{'h', "help"});
    args::ArgFlag<int> integer(parser, "integer", "The integer flag", args::Matcher({'i'}));
    args::ArgFlagList<char> characters(parser, "characters", "The character flag", args::Matcher({'c'}));
    args::PosArg<std::string> foo(parser, "foo", "The foo position");
    args::PosArgList<double> numbers(parser, "numbers", "The numbers position list");
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    catch (args::ValidationError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    if (integer) { std::cout << "i: " << integer.value << std::endl; }
    if (characters) { for (const auto ch: characters.values) { std::cout << "c: " << ch << std::endl; } }
    if (foo) { std::cout << "f: " << foo.value << std::endl; }
    if (numbers) { for (const auto nm: numbers.values) { std::cout << "n: " << nm << std::endl; } }
    return 0;
}
```

```shell
% ./test -h
  ./test {OPTIONS} [foo] [numbers...] 

    This is a test program. 

  OPTIONS:

      -h, --help         Display this help menu 
      -i integer         The integer flag 
      -c characters      The character flag 
      foo                The foo position 
      numbers            The numbers position list 
      "--" can be used to terminate flag options and force all following
      arguments to be treated as positional options 

    This goes after the options. 
 % ./test -i 5
i: 5
 % ./test -i 5.2
Argument 'integer' received invalid value type '5.2'
  ./test {OPTIONS} [foo] [numbers...] 
 % ./test -c 1 -c 2 -c 3
c: 1
c: 2
c: 3
 % 
 % ./test 1 2 3 4 5 6 7 8 9
f: 1
n: 2
n: 3
n: 4
n: 5
n: 6
n: 7
n: 8
n: 9
 % ./test 1 2 3 4 5 6 7 8 9 a
Argument 'numbers' received invalid value type 'a'
  ./test {OPTIONS} [foo] [numbers...] 

    This is a test program. 
...
```

# Custom type parsers (here we use std::tuple)

```cpp
#include <iostream>
#include <tuple>
#include <args.hxx>
std::istream& operator>>(std::istream& is, std::tuple<int, int>& ints)
{
    is >> std::get<0>(ints);
    is.get();
    is >> std::get<1>(ints);
    return is;
}

void DoublesReader(const std::string &name, const std::string &value, std::tuple<double, double> &destination)
{
    size_t commapos = 0;
    std::get<0>(destination) = std::stod(value, &commapos);
    std::get<1>(destination) = std::stod(std::string(value, commapos + 1));
}

int main(int argc, char **argv)
{
    args::ArgumentParser parser("This is a test program.");
    args::PosArg<std::tuple<int, int>> ints(parser, "INTS", "This takes a pair of integers.");
    args::PosArg<std::tuple<double, double>, DoublesReader> doubles(parser, "DOUBLES", "This takes a pair of doubles.");
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    if (ints)
    {
        std::cout << "ints found: " << std::get<0>(ints.value) << " and " << std::get<1>(ints.value) << std::endl;
    }
    if (doubles)
    {
        std::cout << "doubles found: " << std::get<0>(doubles.value) << " and " << std::get<1>(doubles.value) << std::endl;
    }
    return 0;
}
```

```shell
 % ./test -h
Argument could not be matched: 'h'
  ./test [INTS] [DOUBLES] 

    This is a test program. 

  OPTIONS:

      INTS               This takes a pair of integers. 
      DOUBLES            This takes a pair of doubles. 

 % ./test 5
ints found: 5 and 0
 % ./test 5,8
ints found: 5 and 8
 % ./test 5,8 2.4,8
ints found: 5 and 8
doubles found: 2.4 and 8
 % ./test 5,8 2.4, 
terminate called after throwing an instance of 'std::invalid_argument'
  what():  stod
zsh: abort      ./test 5,8 2.4,
 % ./test 5,8 2.4 
terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::basic_string: __pos (which is 4) > this->size() (which is 3)
zsh: abort      ./test 5,8 2.4
 % ./test 5,8 2.4-7
ints found: 5 and 8
doubles found: 2.4 and 7
 % ./test 5,8 2.4,-7
ints found: 5 and 8
doubles found: 2.4 and -7
```

As you can see, with your own types, validation can get a little weird.  Make
sure to check and throw a parsing error (or whatever error you want to catch)
if you can't fully deduce your type.  The built-in validator will only throw if
there are unextracted characters left in the stream.

## Long descriptions and proper wrapping and listing

```cpp
#include <iostream>
#include <args.hxx>
int main(int argc, char **argv)
{
    args::ArgumentParser parser("This is a test program with a really long description that is probably going to have to be wrapped across multiple different lines.  This is a test to see how the line wrapping works", "This goes after the options.  This epilog is also long enough that it will have to be properly wrapped to display correctly on the screen");
    args::HelpFlag help(parser, "HELP", "Show this help menu.", args::Matcher{'h', "help"});
    args::ArgFlag<std::string> foo(parser, "FOO", "The foo flag.", args::Matcher{'a', 'b', 'c', "a", "b", "c", "the-foo-flag"});
    args::ArgFlag<std::string> bar(parser, "BAR", "The bar flag.  This one has a lot of options, and will need wrapping in the description, along with its long flag list.", args::Matcher{'d', 'e', 'f', "d", "e", "f"});
    args::ArgFlag<std::string> baz(parser, "FOO", "The baz flag.  This one has a lot of options, and will need wrapping in the description, even with its short flag list.", args::Matcher({"baz"}));
    args::PosArg<std::string> pos1(parser, "POS1", "The pos1 argument.");
    args::PosArgList<std::string> poslist1(parser, "POSLIST1", "The poslist1 argument.");
    args::PosArg<std::string> pos2(parser, "POS2", "The pos2 argument.");
    args::PosArgList<std::string> poslist2(parser, "POSLIST2", "The poslist2 argument.");
    args::PosArg<std::string> pos3(parser, "POS3", "The pos3 argument.");
    args::PosArgList<std::string> poslist3(parser, "POSLIST3", "The poslist3 argument.");
    args::PosArg<std::string> pos4(parser, "POS4", "The pos4 argument.");
    args::PosArgList<std::string> poslist4(parser, "POSLIST4", "The poslist4 argument.");
    args::PosArg<std::string> pos5(parser, "POS5", "The pos5 argument.");
    args::PosArgList<std::string> poslist5(parser, "POSLIST5", "The poslist5 argument.");
    args::PosArg<std::string> pos6(parser, "POS6", "The pos6 argument.");
    args::PosArgList<std::string> poslist6(parser, "POSLIST6", "The poslist6 argument.");
    args::PosArg<std::string> pos7(parser, "POS7", "The pos7 argument.");
    args::PosArgList<std::string> poslist7(parser, "POSLIST7", "The poslist7 argument.");
    args::PosArg<std::string> pos8(parser, "POS8", "The pos8 argument.");
    args::PosArgList<std::string> poslist8(parser, "POSLIST8", "The poslist8 argument.");
    args::PosArg<std::string> pos9(parser, "POS9", "The pos9 argument.");
    args::PosArgList<std::string> poslist9(parser, "POSLIST9", "The poslist9 argument.");
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    catch (args::ValidationError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    return 0;
}
```

```shell
 % ./test -h
  ./test {OPTIONS} [POS1] [POSLIST1...] [POS2] [POSLIST2...] [POS3]
      [POSLIST3...] [POS4] [POSLIST4...] [POS5] [POSLIST5...] [POS6]
      [POSLIST6...] [POS7] [POSLIST7...] [POS8] [POSLIST8...] [POS9]
      [POSLIST9...] 

    This is a test program with a really long description that is probably going
    to have to be wrapped across multiple different lines. This is a test to see
    how the line wrapping works 

  OPTIONS:

      -h, --help         Show this help menu. 
      -a FOO, -b FOO, -c FOO, --a FOO, --b FOO, --c FOO, --the-foo-flag FOO
                         The foo flag. 
      -d BAR, -e BAR, -f BAR, --d BAR, --e BAR, --f BAR
                         The bar flag. This one has a lot of options, and will
                         need wrapping in the description, along with its long
                         flag list. 
      --baz FOO          The baz flag. This one has a lot of options, and will
                         need wrapping in the description, even with its short
                         flag list. 
      POS1               The pos1 argument. 
      POSLIST1           The poslist1 argument. 
      POS2               The pos2 argument. 
      POSLIST2           The poslist2 argument. 
      POS3               The pos3 argument. 
      POSLIST3           The poslist3 argument. 
      POS4               The pos4 argument. 
      POSLIST4           The poslist4 argument. 
      POS5               The pos5 argument. 
      POSLIST5           The poslist5 argument. 
      POS6               The pos6 argument. 
      POSLIST6           The poslist6 argument. 
      POS7               The pos7 argument. 
      POSLIST7           The poslist7 argument. 
      POS8               The pos8 argument. 
      POSLIST8           The poslist8 argument. 
      POS9               The pos9 argument. 
      POSLIST9           The poslist9 argument. 
      "--" can be used to terminate flag options and force all following
      arguments to be treated as positional options 

    This goes after the options. This epilog is also long enough that it will
    have to be properly wrapped to display correctly on the screen 
 %
```

## Customizing parser prefixes

### dd-style

```cpp
#include <iostream>
#include <args.hxx>
int main(int argc, char **argv)
{
    args::ArgumentParser parser("This command likes to break your disks");
    parser.LongPrefix("");
    parser.LongSeparator("=");
    args::HelpFlag help(parser, "HELP", "Show this help menu.", args::Matcher({"help"}));
    args::ArgFlag<long> bs(parser, "BYTES", "Block size", args::Matcher({"bs"}), 512);
    args::ArgFlag<long> skip(parser, "BYTES", "Bytes to skip", args::Matcher({"skip"}), 0);
    args::ArgFlag<std::string> input(parser, "BLOCK SIZE", "Block size", args::Matcher({"if"}));
    args::ArgFlag<std::string> output(parser, "BLOCK SIZE", "Block size", args::Matcher({"of"}));
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    catch (args::ValidationError e)
    {
        std::cerr << e.what() << std::endl;
        std::cerr << parser;
        return 1;
    }
    std::cout << "bs = " << bs.value << std::endl;
    std::cout << "skip = " << skip.value << std::endl;
    if (input) { std::cout << "if = " << input.value << std::endl; }
    if (output) { std::cout << "of = " << output.value << std::endl; }
    return 0;
}
```

```shell
 % ./test help
  ./test {OPTIONS} 

    This command likes to break your disks 

  OPTIONS:

      help               Show this help menu. 
      bs BYTES           Block size 
      skip BYTES         Bytes to skip 
      if BLOCK_SIZE      Block size 
      of BLOCK_SIZE      Block size 

 % ./test bs=1024 skip=7 if=/tmp/input
bs = 1024
skip = 7
if = /tmp/input
```

### Windows style

The code is the same as above, but the two lines are replaced out:

```cpp
parser.LongPrefix("/");
parser.LongSeparator(":");
```

```shell
 % ./test /help     
  ./test {OPTIONS} 

    This command likes to break your disks 

  OPTIONS:

      /help              Show this help menu. 
      /bs BYTES          Block size 
      /skip BYTES        Bytes to skip 
      /if BLOCK_SIZE     Block size 
      /of BLOCK_SIZE     Block size 

 % ./test /bs:72 /skip:87 /if:/tmp/test.txt
bs = 72
skip = 87
if = /tmp/test.txt
 % 
```

## Group nesting help menu text

```cpp
#include <iostream>
#include <args.hxx>
int main(int argc, char **argv)
{
    args::ArgumentParser parser("This is a test program.", "This goes after the options.");
    args::Group xorgroup(parser, "this group provides xor validation:", args::Group::Validators::Xor);
    args::Flag a(xorgroup, "a", "test flag", args::Matcher({'a'}));
    args::Flag b(xorgroup, "b", "test flag", args::Matcher({'b'}));
    args::Flag c(xorgroup, "c", "test flag", args::Matcher({'c'}));
    args::Group nxor(xorgroup, "this group provides all-or-none (nxor) validation:", args::Group::Validators::AllOrNone);
    args::Flag d(nxor, "d", "test flag", args::Matcher({'d'}));
    args::Flag e(nxor, "e", "test flag", args::Matcher({'e'}));
    args::Flag f(nxor, "f", "test flag", args::Matcher({'f'}));
    args::Group nxor2(nxor, "this group provides all-or-none (nxor2) validation:", args::Group::Validators::AllOrNone);
    args::Flag i(nxor2, "i", "test flag", args::Matcher({'i'}));
    args::Flag j(nxor2, "j", "test flag", args::Matcher({'j'}));
    args::Flag k(nxor2, "k", "test flag", args::Matcher({'k'}));
    args::Group nxor3(nxor, "this group provides all-or-none (nxor3) validation:", args::Group::Validators::AllOrNone);
    args::Flag l(nxor3, "l", "test flag", args::Matcher({'l'}));
    args::Flag m(nxor3, "m", "test flag", args::Matcher({'m'}));
    args::Flag n(nxor3, "n", "test flag", args::Matcher({'n'}));
    args::Group atleastone(xorgroup, "this group provides at-least-one validation:", args::Group::Validators::AtLeastOne);
    args::Flag g(atleastone, "g", "test flag", args::Matcher({'g'}));
    args::Flag o(atleastone, "o", "test flag", args::Matcher({'o'}));
    args::HelpFlag help(parser, "help", "Show this help menu", args::Matcher{'h', "help"});
    try
    {
        parser.ParseCLI(argc, argv);
    }
    catch (args::Help)
    {
        std::cout << parser;
        return 0;
    }
    catch (args::ParseError e)
    {
        std::cerr << e.what() << std::endl;
        parser.Help(std::cerr);
        return 1;
    }
    catch (args::ValidationError e)
    {
        std::cerr << e.what() << std::endl;
        parser.Help(std::cerr);
        return 1;
    }
    return 0;
}
```

```shell
 % /tmp/test -h
  /tmp/test {OPTIONS} 

    This is a test program. 

  OPTIONS:

                         this group provides xor validation: 
        -a                 test flag 
        -b                 test flag 
        -c                 test flag 
                           this group provides all-or-none (nxor) validation: 
          -d                 test flag 
          -e                 test flag 
          -f                 test flag 
                             this group provides all-or-none (nxor2) validation:
            -i                 test flag 
            -j                 test flag 
            -k                 test flag 
                             this group provides all-or-none (nxor3) validation:
            -l                 test flag 
            -m                 test flag 
            -n                 test flag 
                           this group provides at-least-one validation: 
          -g                 test flag 
          -o                 test flag 
      -h, --help         Show this help menu 

    This goes after the options. 
 %                                                                                
```