7 ms·

It just makes it easier to read the magnitude of a number and get that extra visual reassurance that it's correct. It's not easy to (quickly) tell the differen

• ufo 12y ago
  The bigger reason why you can't use commas is because commas are already an operator in c++. 1,2 is an expression that evaluates to 2. Dunno why they didn't use underscores though.
  • jasode 12y ago
    The "already an operator" can be a factor in the design reasoning but if they really really wanted to, they could have made the comma syntax for digit separators by modifying the parsing grammar: e.g. a special prefix and/or contextual parsing. For example, the "->" was already an operator for pointer indirection but it was reused for lambda definitions. The "[]" was already used for array subscript indexes but was reused for lambda captures.
    • chappar 12y ago
      You can't do that for ",", because it will break the existing code. For example, int x = 0; x = 1,2; is perfectly valid pre c++11 code. This will assign 1 to x. Now if you make "," as digit separator, it will assign 12 to x
      • jasode 12y ago
        I mentioned the possibility of a special prefix in my previous post. In other words, that parsing ambiguity goes away if the standards committee wanted to define a special prefix such as 'd', 'k', or '_' to inform the parser that the next comma is a "digit separator" instead of "comma operator" such as _1,000,000 . E.g. there's already intelligence about commas in the parser to disambiguate function calls with commas as in "repositionxyz(914,348,122)" Or, they could have defined C++14 to simply invalidate your example syntax of "x=1,2". As an example, the "auto" keyword was made a "breaking change" such that "for (auto int i = 0;;)" no longer compiles. The bottom line is that there are a myriad of ways to address (potential) parsing ambiguities when introducing new language features and syntax. (Whether or not a comma digit separator is worth the clumsier syntax of a special prefix or inflicting the pain of a breaking change is a separate concept.)
        • Someone 12y ago
          C++ doesn't have the friendliest grammar for addressing potential parsing ambiguities. As an example, your proposed solutions _1,000,000 k1,000,000 Both are already valid if variables or functions _1 or k1 are in scope, and evaluate to (octal) zero. And I haven't checked, but it would guess that invalidating "x=1,2" in the parser would not be "simple". I cannot think of a reason, but it also might turn out to be more common then one would think due to macro expansions.
  • flebron 12y ago
    Underscores are already being used for user defined literals.
    • drdaeman 12y ago
      User-defined literals can't generally start with a digit, so it should be perfectly fine to allow 1_000_000 syntax for 1000000. Or I'm forgetting something?
      • jeorgun 12y ago
        Hexadecimal numbers, probably. 0x001_f05 would be ambiguous.
        • AnimalMuppet 12y ago
          I don't think that's it. 0x001_f05 starts with 0, which is still not something an identifier can do.
          • plorkyeran 12y ago
            0x001_f05 could be a UDL named f05 which should be passed 0x001.
            • AnimalMuppet 12y ago
              Oh. UDLs are a new one to me. I didn't know that was in the language. I stand corrected.
      • nightcracker 12y ago
        Where do you get this information from, because it's entirely incorrect.
• Pxtl 12y ago
  I would've gone with spaces. Those are the official standard here in Canada as a pragmatic compromise between anglos and francos that have opposing usage of comma/dot. So instead of 1,234.56789 (English) or 1.234,56789 (French) we do 1 234.56789 (international) [0-9]+ [0-9]+ has no meaning in C++, so using space for magnitude decorations would have worked.
  • detrino 12y ago
    Have you considered if this would fit with C++'s grammar?
    • Pxtl 12y ago
      Briefly, but I think there are like three people in the world that fully grok C++ grammar, and I'm definitely not one of them. I just know that C++ generally has some kind of infix operator or delimiter between pairs of immediate data or variables, I'm pretty sure it's currently just a compiler error in every case.
      • nightcracker 12y ago
        Except this is not C++ grammar, this is simple lexical analysis. And separating by spaces would work fine.
      • dallos 12y ago
        What about semantics? Probably 0.
  • repsilat 12y ago
    Nice, it fits well with the "adjacent strings are automatically concatenated by the compiler" rule, too.