Input string C++ double chevron

Question

I'm currently trying to use a double chevron in a string for "<<" and ">>" to represent bit shifting. However, my program does not seem to recognize using double chevrons for any input. If I change it to any other string, it works perfectly.

derpleft will work, however "<<" will not work.

keywords_["derpleft"]  = keywords_["<<"] = make<BitShiftLeft>();
keywords_["derpright"] = keywords_[">>"] =  make<BitShiftRight>();

dictionary_type keywords_;

typedef std::map<string_type,Token::pointer_type>   dictionary_type;

typedef std::string string_type;

Why do I have a feeling this has to do with using `char` for something that it can't hold? — chris, Dec 08 '12 at 02:24
keywords_["derpleft"] = keywords_["<<"] = make(); keywords_["derpright"] = keywords_[">>"] = make(); derpleft works, not << It's made up of: typedef std::string string_type; — Vernah, Dec 08 '12 at 02:31
Are you actually inputting two less than signs, and not gullets or something? — chris, Dec 08 '12 at 02:34
Your program is upside down. The compiler reads from top to bottom. — Benjamin Lindley, Dec 08 '12 at 03:23
I just took segments out of it to show that keywords is a string. — Vernah, Dec 08 '12 at 03:42
How are you getting your tokens? We need more code than this to help. — Tawnos, Dec 08 '12 at 04:31
As Tawnos said, we need more code. Nothing looks in the pseudo-code you've posted. But then again, nothing *really* looks wrong in pseudo-code. — Nik Bougalis, Dec 08 '12 at 06:04

score 0 · Answer 1 · answered Dec 08 '12 at 05:56

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I just don't understand this statement:

keywords_["derpleft"]  = keywords_["<<"] = make<BitShiftLeft>();

It seems you want << and derpleft to point to (store) the value returned by make<BitShiftLeft> call. In that case, why not simply it as follows:

keywords_["derpleft"]  = make<BitShiftLeft>();
keywords_["<<"] =  make<BitShiftLeft>();

You may store the value of make call in some local variable (auto keyword preferred).

And most importantly, you did not mention what the problem is!

answered Dec 08 '12 at 05:56

Ajay

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It's *very* common usage to do `x = z = somefunction()` to set z and x to the output of somefunction(). Splitting that into two different calls with result in `somefunction()` being called twice (which you may not want to do) and can be harder to maintain. – Nik Bougalis Dec 08 '12 at 06:02
Yeah, I am aware of that! But it doesn't look good in the code posted above. `map::operator[]` will be called as LValue, then RValue, then LValue. I haven't tried, but how what about `keywords["<<"]` call - one call or two calls? – Ajay Dec 08 '12 at 06:07

score 0 · Answer 2 · answered Jan 09 '13 at 21:29

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I forgot to close this thread, but the issue was I did not set a boolean to true in one of my editor functions. It was simply a logic error that I created.

answered Jan 09 '13 at 21:29

Vernah

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Input string C++ double chevron

2 Answers2