CODEWITHSUNDEEP
c++istream
Anton
Anton

Reputation: 43

How do i read bool value using std::istream

I'm trying to read different formats as csv and json. One time boolean value is given by string "1" or "0" and another time by string "true" or "false". Now i use uniform template function that converts that string to bool. but std::istream can't read both bool formats simultaneously. If flag std::ios::boolalpha is set, exception grows while reading "1" and vise versa. I want to read both ways, and i don't know what format is now.

Upvotes: 2

Views: 3684

Answers (1)

sehe
sehe

Reputation: 393467

You can always just use a local stream to read it:

 bool read_bool(std::istream& is) {
     std::istream local(is.rdbuf());
     // now the default stream options are in force

     bool v;
     if (!local >> v)
         throw std::runtime_error("parse error");

Otherwise, you can choose to parse your input manually:

 std::string s;
 if (is >> s) {
      if (s == "0" || s == "false")
           //
      else if (s == "1" || ...

etc.

You can also use something like

  • Boost Lexicalcast

  • Boost Spirit

    qi::symbols<char, bool> table;
table.add("0",false)("1",true)("false",false)("true",true);

bool v;
if (is >> qi::match(table, v))
    std::cout << "Parsed: " << v << "\n";

Upvotes: 3

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