Question

I have such a structure (for some reason I cant just use an array):

  struct OperatorData 
  {
    char m_record_0[RIX_OPERATOR_CONFIG_SIZE];
    char m_record_1[RIX_OPERATOR_CONFIG_SIZE];
    //....
    char m_record_9[RIX_OPERATOR_CONFIG_SIZE];
  };

And I am trying to calculate amount of fields at compile-time:

enum {fieldsAmount = sizeof(OperatorData) / sizeof(OperatorData::m_record_0)};

And the compiler reports such a message:

Error:  #245: a nonstatic member reference must be relative to a specific object
  enum{fieldsAmount = sizeof(OperatorData) / sizeof(OperatorData::m_record_0)};
                                                                  ^

I use keil uVision3 V3.60.
It doesn’t matter where I place enum declaration inside or outside the structure.
Why can’t the compiler take size of this membmer?

Answer 1

It looks like your compiler doesn’t support C++11 that allows the use of Type::member in unevaluated expressions. You’ll have to manufacture an expression of the correct type, something like:

OperatorData* noImpl();

enum{fieldsAmount = sizeof(OperatorData) / sizeof(noImpl()->m_record_0)};