使用std :: bitset

Question

There is a class definition and some bool functions which test some attributes

  class MemCmd
  {
      friend class Packet;
      public:
        enum Command
        {
          InvalidCmd,
          ReadReq,
          ReadResp,
          NUM_MEM_CMDS
        };
      private:
        enum Attribute
        {
          IsRead,         
          IsWrite,             
          NeedsResponse,  
          NUM_COMMAND_ATTRIBUTES
        };

        struct CommandInfo
        {
          const std::bitset<NUM_COMMAND_ATTRIBUTES> attributes;
          const Command response;
          const std::string str;
        };
        static const CommandInfo commandInfo[];
      private:
        bool
        testCmdAttrib(MemCmd::Attribute attrib) const
        {
          return commandInfo[cmd].attributes[attrib] != 0;
        }
      public:
        bool isRead() const         { return testCmdAttrib(IsRead); }
        bool isWrite() const        { return testCmdAttrib(IsWrite); }
        bool needsResponse() const  { return testCmdAttrib(NeedsResponse); }
  };

The question is how can I set NeedsResponse to true or false prior to calling needsResponse()

Please note that attributes is of type std::bitset

UPDATE:

I wrote this function:

void
setCmdAttrib(MemCmd::Attribute attrib, bool flag) 
{
    commandInfo[cmd].attributes[attrib] = flag;   // ERROR
}

void setNeedsResponse(bool flag)   { setCmdAttrib(NeedsResponse, flag); }

But I get this error:

error: lvalue required as left operand of assignment

Answer 1

From the comments:

There are two problems here

1. Data members that are const must be initialized in the class constructor.
2. If the members are const there is no way to change them later.

So, initialize (at least) the members that are supposed to have a constant value. Remove const from the members you intend to change later.