Building command line applications

Question

How can I move away from (in c++) the annoying menus like:

(a) Do something (b) Do something else (c) Do that 3rd thing (x) exit

Basically I want to be able to run the program then do something like "calc 32 / 5" or "open data.csv", where obviously I would have written the code for "calc" and "open". Just a shove in the right direction would be great, I am sure I can figure it all out, I just need something to google-fu.

You want to write an interpreter? Lots of resources around here: http://stackoverflow.com/questions/1669/learning-to-write-a-compiler and http://stackoverflow.com/questions/294852/references-needed-for-implementing-an-interpreter-in-c-c. If this is your question that second link is a duplicate. — dmckee --- ex-moderator kitten, Sep 17 '09 at 23:53
Also http://stackoverflow.com/questions/41785/learning-resources-on-parsers-interpreters-and-compilers — dmckee --- ex-moderator kitten, Sep 17 '09 at 23:53

score 3 · Answer 1 · answered Sep 17 '09 at 23:49

I think you want to do something like this:

string cmd;
cout << "Enter your command:" << endl;
cin >> cmd;
if(cmd == "open") {
    // read file name and open file
} else if (cmd == "calc") {
    // read and evaluate expression
} ...

Though depending on how complex you want your command language to be, a more elaborate design (maybe even using a parser generator) might be appropriate.

score 2 · Answer 2 · answered Sep 17 '09 at 23:48

2

What you want is a command line parser. I can't remember the name, but there is actually a design pattern to this. However, this site gives you some sample code you can use to write one. Hope that's not giving you too much of the answer :)

answered Sep 17 '09 at 23:48

Chris Thompson

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I'm not sure he does want a command line parser; he's wanting to input commands after the program is running. – Matthew Talbert Sep 17 '09 at 23:49
Ah you're absolutely right, I misread that. I know there is a design pattern for this though... – Chris Thompson Sep 17 '09 at 23:53

score 2 · Accepted Answer · answered Sep 17 '09 at 23:49

2

You should pick up The C++ Programming Language, which is the book on C++ (there are others, but this one is great). It has an example program, spread over a few chapters, on tokenizing, parsing arguments, and making a calculator.

answered Sep 17 '09 at 23:49

Chris Simmons

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I have that book! (In white hardback with 2 ribbon bookmarks no less!). It was waay beyond me in the first chapter and just couldnt get into it, but it may be time to give it another go. – Silvanus Sep 17 '09 at 23:55

score 0 · Answer 4 · answered Sep 17 '09 at 23:49

0

Instead of looking for input like a, b, etc, just ask for generic input. Split the input at spaces, do a "switch" on the first one to match it up to your function calls, treat the rest as arguments.

answered Sep 17 '09 at 23:49

Matthew Talbert

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score 0 · Answer 5 · answered Sep 17 '09 at 23:50

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Is your menu based on a call to getchar()? If you want to allow entering an entire line before processing it, you can use fgets() or, in C++ land, std::getline.

answered Sep 17 '09 at 23:50

Tim Sylvester

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score 0 · Answer 6 · answered Sep 18 '09 at 00:03

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Some folks will package their C++ class definitions as Python classes by adding a Python interface to the C++.

Then they write the top-level interpreter in Python using the built-in cmd library.

answered Sep 18 '09 at 00:03

S.Lott

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score 0 · Answer 7 · answered Sep 18 '09 at 00:11

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Take a look to:

ANTLR which is a very good and easy parser which also generates code on C++.
You can take a look to Natural CLI (java) to get inspired. (Disclaimer: i'm the developer of that project).

answered Sep 18 '09 at 00:11

FerranB

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Building command line applications

7 Answers7