how to define struct inside of class?

Question

I have trouble compiling the code at the bottom. I do this in C all the time but can't do it in C++ when it's inside a class. Could someone enlighten me what is wrong here?

class Parser {

  struct table {
     string first;
     string second;
     string third;
  } c_table [] = {
   "0","a","b",
   "0","c","d",
   "0","e","f",
  };
};

int main() {

  return 0;
}

test.cpp:22:3: error: too many initializers for ‘Parser::table [0]’
test.cpp:22:3: error: could not convert ‘(const char*)"0"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"a"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"b"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"0"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"c"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"d"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"0"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"e"’ from ‘const char*’ to ‘Parser::table’
test.cpp:22:3: error: could not convert ‘(const char*)"f"’ from ‘const char*’ to ‘Parser::table’

Answer 1

Pre-C++11 you're not allowed to initialize members inside class definition (except for static const members of integral types). This leaves you no other choice but to fill it inside a body of a constructor.

In C++11, you can have an initializer, but

• you need to add another set of braces for each array element and
• you need to specify the size of the array

---

#include <string>
using std::string;

class Parser {

  struct table {
     string first;
     string second;
     string third;
  } c_table [3] = {
   {"0","a","b"}, // <-- note the braces
   {"0","c","d"},
   {"0","e","f"}
  };
};

Live Example

I think the reason you need to specify the dimension is because the initializer from the class definition can be trumped over by a member initializer inside some constructor, which could have a different element count.