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Show HN: Add a command-line interface to any C++ program

119 points by chrisaycock 5y ago

HMH 5y ago
I haven't really touched C++ for a few years and it seems due to its lack of a nice package manager single header libraries are getting more and more poplar. Does this mean I should expect compilation time to significantly increase during development as headers need to be recompiled every time?
- pjmlp 5y ago
  In the meantime two big contenders raised up, vcpkg alongside NuGET from Microsoft (also does Mac and Linux), and conan. Personally I dislike conan, because package managers should be written in the language of the community they serve, but that is me. Thankfully, both support binary libraries. Then there are modules, which on Visual C++'s case are going along quite well. Anyone that bothers using header only libraries only has themselves to blame for waiting for builds, they are a plague from users that pretend C and C++ are scripting languages.
  - ngneer 5y ago
    Conan has been very useful to me
  - twqas 5y ago
    Unfortunately Microsoft is addicted to telemetry, so vcpkg has that. I did not bother checking for NuGET. Header-only libraries can give substantial speedups (25% in extreme cases).
    - pjmlp 5y ago
      You can disable it. I really would like to see benchmarks versus proper use of binary libraries.
      - inetknght 5y ago
        > You can disable it. I shouldn't have to think about it; I shouldn't have to explicitly opt-out to have privacy. Telemetry should always be opt-in, and not opted-in by default.
        ranger_danger 5y ago
        The problem is, as a developer trying to fix issues, telemetry can be extremely helpful... but if it's solely opt-in, then virtually nobody will actually use it, and then what's the point.
        kjs3 5y ago
        So your developer issues should trump my user issues?
        TillE 5y ago
        It tells you to just recompile with -disableMetrics if you want, it's really not a huge deal. It's not like Windows.
        kjs3 5y ago
        So as a user, I have to recompile in deference to making things easier for the developer. Definitely not like Windows...for all their sins, they don't pull entitled BS like that on users.
  - jstimpfle 5y ago
    "Header only" might be a bad name, in my perception what it really means is "you can drop the code files into your project; we won't annoy you with our own over-engineered build system". Slow-compiling APIs can be made in any form, whether "header only" or not. C++ template APIs cannot be compiled separately and can cause long compile times for all transitively dependent translation units. For example, stb_image.h is a single file that is 1 copy+paste from github away. It compiles quite quickly, and often you will need it alongside only a single .c file in your project, but anyway it's extremely easy to compile it separately. All you have to do is cut+paste the implementation part to a separate .c file.
    - pjmlp 5y ago
      Templates can be instanted for common types and consumed via binary libraries. Also modules support templates just fine. Indeed, header only libs are just doing PHP like programming.
    - moonchrome 5y ago
      Copy pasting shit in your repo means you are responsible for maintaining that code and need to keep track of upstream manually. Especially in c++ where memory bugs are prevalent, this sounds like a terrible idea.
- mrich 5y ago
  In the case here most of the code is templates and macros, so a cpp wouldn't save much.
- ranger_danger 5y ago
  Just include that header in a separate C/C++ file that has no other purpose, then you won't have to recompile it every time you change something elsewhere.
  - corysama 5y ago
    Yeah. "header only" had really caught on because it is a catchy term that is simple to understand. But, what I really, really wish caught on would be "single cpp file" with the expectation that you are capable of adding a single, self-contained source file to whatever build system you happen to be using.
    - electroly 5y ago
      That's often what "header only" libraries really are -- you create your own .cpp file, define a particular preprocessor symbol, and then include the header which will then produce the implementation in that translation unit. Without the symbol defined you only get the interface, suitable for including in other translation units.
nuerow 5y ago
Obligatory reference to Boost's Program_options , which is as close to a standard way to handle command line options in C++ there is. https://www.boost.org/doc/libs/1_77_0/doc/html/program_options.html https://www.boost.org/doc/libs/1_77_0/doc/html/program_optio...
- nly 5y ago
  As mentioned this isn't wholly relevent because TFA is about adding a REPL. Nonetheless I prefer to use cxxopts[0] over BPO if I can justify the extra submodule [0] https://github.com/jarro2783/cxxopts https://github.com/jarro2783/cxxopts
azalemeth 5y ago
What about gnu Genopt? I have really enjoyed using it, although it's perhaps pure C rather than C++.
- jcul 5y ago
  I haven't used Genopt, it looks cool. At first I thought you meant getopt, which it looks like Genopt is built on. However I think Genopt is concerned with command line arguments. This is about an interactive command line interface, like a REPL. So you type command and it calls functions interactivly. This kind of thing can be a lot of work to do right, so I think this header looks great. I'm looking forward to trying it out.
  - ryandrake 5y ago
    Yea, I was a little confused by the "command line" claim, too. Like, where is it parsing argv and argc, and does it support long style and short style options? Title should say "Add a REPL interface to any C++ program"
eps 5y ago
Clean and simple API, clever implementation. Very nicely done. Saying as someone who worked on a cli framework for network devices in the past and quite enjoyed it. It was in C though, so it wasn't as terse.
chrisaycock 5y ago
I wrote this to add a REPL-like interface to existing programs. It can call normal functions with automatic parsing and type safety. class Arithmetic : public CommandInterface { int add(int x, int y) { return x + y; } void register_commands() override { register_command(&Arithmetic::add, "add", "Add two numbers"); } }; Simply evaluate a string to invoke the function. Arithmetic arithmetic; arithmetic.eval("add 3 4"); // returns "7" The user can place the eval() call behind any interface that has a string for its input and output. I personally use it behind a TCP socket on my trading application; I can query my strategy's state and change its parameters on the fly. If funky C++ interests you, the prop firm I work for is looking to hire engineers. Feel free to contact me directly: chris -AT- chrisaycock -DOT- com
- dmalecaut 5y ago
  Prop firms sure like their esoteric C++!
  - sfgweilr4f 5y ago
    "prop"?
    - dmalecaut 5y ago
      Proprietary trading firm
- choeger 5y ago
  Nice work. Thanks for releasing it as free software. If I understand the design correctly, one can provide a custom argument parser by specializing lexical_cast?
  - chrisaycock 5y ago
    Yes, in theory. I've never tried to specialize lexical_cast since it's a Boost library and likely has its own assumptions. But I imagine it's possible if you want to handle things like arrays or user-defined types.
anon-user-101 5y ago
To be fair to chrisaycock, this library it to actually add a runtime REPL rather than a command line interface. So the link to boost progam options is irrelevant.
jb1991 5y ago
Why is the example flushing the output buffer twice with endl? This is naive, and a simple new line is probably intended for at least one of those flushes.
- jkrubin 5y ago
  I think it’s pretty cool regardless. Don’t be a weenie.
- eps 5y ago
  The only comment that you think is worthy making after looking at OP's project is about adding a blank line in front of a prompt, in an example? Show some rudimentary respect towards the work of others by not nitpicking on trivialities.
  - deleted 5y ago
    [deleted]
- deleted 5y ago
  [deleted]
svalorzen 5y ago
Nice work! I maintain a library, cpp-readline [1], with a very similar API. The main difference is that relegates the REPL part to GNU readline. You do have the additional dependency, but on the other hand it automatically adds history and other nice-to-have features. [1]: https://github.com/Svalorzen/cpp-readline https://github.com/Svalorzen/cpp-readline
ulnarkressty 5y ago
How does this compare to boost::spirit? I tried some years ago to make something similar but gave up due to the huge compile times for even simple grammar parsing.
- chrisaycock 5y ago
  Spirit is a parser combinator. That's if you want to design a whole language from scratch. My library is for single-name commands that can take simple parameters. You can't define your own language here.
butwhywhyoh 5y ago
This isn't a command-line interface, this is a REPL. Very confusing title.
cozzyd 5y ago
Note that you can use cling/ROOT an actual C++ repl.

119 points by chrisaycock 5y ago

HMH 5y ago

I haven't really touched C++ for a few years and it seems due to its lack of a nice package manager single header libraries are getting more and more poplar. Does this mean I should expect compilation time to significantly increase during development as headers need to be recompiled every time?

pjmlp 5y ago
In the meantime two big contenders raised up, vcpkg alongside NuGET from Microsoft (also does Mac and Linux), and conan. Personally I dislike conan, because package managers should be written in the language of the community they serve, but that is me. Thankfully, both support binary libraries. Then there are modules, which on Visual C++'s case are going along quite well. Anyone that bothers using header only libraries only has themselves to blame for waiting for builds, they are a plague from users that pretend C and C++ are scripting languages.
- ngneer 5y ago
  Conan has been very useful to me
- twqas 5y ago
  Unfortunately Microsoft is addicted to telemetry, so vcpkg has that. I did not bother checking for NuGET. Header-only libraries can give substantial speedups (25% in extreme cases).
  - pjmlp 5y ago
    You can disable it. I really would like to see benchmarks versus proper use of binary libraries.
    - inetknght 5y ago
      > You can disable it. I shouldn't have to think about it; I shouldn't have to explicitly opt-out to have privacy. Telemetry should always be opt-in, and not opted-in by default.
      - ranger_danger 5y ago
        The problem is, as a developer trying to fix issues, telemetry can be extremely helpful... but if it's solely opt-in, then virtually nobody will actually use it, and then what's the point.
        kjs3 5y ago
        So your developer issues should trump my user issues?
        TillE 5y ago
        It tells you to just recompile with -disableMetrics if you want, it's really not a huge deal. It's not like Windows.
        kjs3 5y ago
        So as a user, I have to recompile in deference to making things easier for the developer. Definitely not like Windows...for all their sins, they don't pull entitled BS like that on users.
- jstimpfle 5y ago
  "Header only" might be a bad name, in my perception what it really means is "you can drop the code files into your project; we won't annoy you with our own over-engineered build system". Slow-compiling APIs can be made in any form, whether "header only" or not. C++ template APIs cannot be compiled separately and can cause long compile times for all transitively dependent translation units. For example, stb_image.h is a single file that is 1 copy+paste from github away. It compiles quite quickly, and often you will need it alongside only a single .c file in your project, but anyway it's extremely easy to compile it separately. All you have to do is cut+paste the implementation part to a separate .c file.
  - pjmlp 5y ago
    Templates can be instanted for common types and consumed via binary libraries. Also modules support templates just fine. Indeed, header only libs are just doing PHP like programming.
  - moonchrome 5y ago
    Copy pasting shit in your repo means you are responsible for maintaining that code and need to keep track of upstream manually. Especially in c++ where memory bugs are prevalent, this sounds like a terrible idea.
mrich 5y ago
In the case here most of the code is templates and macros, so a cpp wouldn't save much.
ranger_danger 5y ago
Just include that header in a separate C/C++ file that has no other purpose, then you won't have to recompile it every time you change something elsewhere.
- corysama 5y ago
  Yeah. "header only" had really caught on because it is a catchy term that is simple to understand. But, what I really, really wish caught on would be "single cpp file" with the expectation that you are capable of adding a single, self-contained source file to whatever build system you happen to be using.
  - electroly 5y ago
    That's often what "header only" libraries really are -- you create your own .cpp file, define a particular preprocessor symbol, and then include the header which will then produce the implementation in that translation unit. Without the symbol defined you only get the interface, suitable for including in other translation units.

nuerow 5y ago

Obligatory reference to Boost's Program_options , which is as close to a standard way to handle command line options in C++ there is. https://www.boost.org/doc/libs/1_77_0/doc/html/program_options.html https://www.boost.org/doc/libs/1_77_0/doc/html/program_optio...

nly 5y ago
As mentioned this isn't wholly relevent because TFA is about adding a REPL. Nonetheless I prefer to use cxxopts[0] over BPO if I can justify the extra submodule [0] https://github.com/jarro2783/cxxopts https://github.com/jarro2783/cxxopts

azalemeth 5y ago

What about gnu Genopt? I have really enjoyed using it, although it's perhaps pure C rather than C++.

jcul 5y ago
I haven't used Genopt, it looks cool. At first I thought you meant getopt, which it looks like Genopt is built on. However I think Genopt is concerned with command line arguments. This is about an interactive command line interface, like a REPL. So you type command and it calls functions interactivly. This kind of thing can be a lot of work to do right, so I think this header looks great. I'm looking forward to trying it out.
- ryandrake 5y ago
  Yea, I was a little confused by the "command line" claim, too. Like, where is it parsing argv and argc, and does it support long style and short style options? Title should say "Add a REPL interface to any C++ program"

eps 5y ago

Clean and simple API, clever implementation. Very nicely done. Saying as someone who worked on a cli framework for network devices in the past and quite enjoyed it. It was in C though, so it wasn't as terse.

chrisaycock 5y ago

I wrote this to add a REPL-like interface to existing programs. It can call normal functions with automatic parsing and type safety. class Arithmetic : public CommandInterface { int add(int x, int y) { return x + y; } void register_commands() override { register_command(&Arithmetic::add, "add", "Add two numbers"); } }; Simply evaluate a string to invoke the function. Arithmetic arithmetic; arithmetic.eval("add 3 4"); // returns "7" The user can place the eval() call behind any interface that has a string for its input and output. I personally use it behind a TCP socket on my trading application; I can query my strategy's state and change its parameters on the fly. If funky C++ interests you, the prop firm I work for is looking to hire engineers. Feel free to contact me directly: chris -AT- chrisaycock -DOT- com

dmalecaut 5y ago
Prop firms sure like their esoteric C++!
- sfgweilr4f 5y ago
  "prop"?
  - dmalecaut 5y ago
    Proprietary trading firm
choeger 5y ago
Nice work. Thanks for releasing it as free software. If I understand the design correctly, one can provide a custom argument parser by specializing lexical_cast?
- chrisaycock 5y ago
  Yes, in theory. I've never tried to specialize lexical_cast since it's a Boost library and likely has its own assumptions. But I imagine it's possible if you want to handle things like arrays or user-defined types.

anon-user-101 5y ago

To be fair to chrisaycock, this library it to actually add a runtime REPL rather than a command line interface. So the link to boost progam options is irrelevant.

jb1991 5y ago

Why is the example flushing the output buffer twice with endl? This is naive, and a simple new line is probably intended for at least one of those flushes.

jkrubin 5y ago
I think it’s pretty cool regardless. Don’t be a weenie.
eps 5y ago
The only comment that you think is worthy making after looking at OP's project is about adding a blank line in front of a prompt, in an example? Show some rudimentary respect towards the work of others by not nitpicking on trivialities.
- deleted 5y ago
  [deleted]
deleted 5y ago
[deleted]

svalorzen 5y ago

Nice work! I maintain a library, cpp-readline [1], with a very similar API. The main difference is that relegates the REPL part to GNU readline. You do have the additional dependency, but on the other hand it automatically adds history and other nice-to-have features. [1]: https://github.com/Svalorzen/cpp-readline https://github.com/Svalorzen/cpp-readline

ulnarkressty 5y ago

How does this compare to boost::spirit? I tried some years ago to make something similar but gave up due to the huge compile times for even simple grammar parsing.

chrisaycock 5y ago
Spirit is a parser combinator. That's if you want to design a whole language from scratch. My library is for single-name commands that can take simple parameters. You can't define your own language here.

butwhywhyoh 5y ago

This isn't a command-line interface, this is a REPL. Very confusing title.

cozzyd 5y ago

Note that you can use cling/ROOT an actual C++ repl.