How to initialize a structure member of a union inside a structure in C++?

Question

I want to port a look-up table of parameters which is an array of structures in C to C++. I read a few questions and understood that the C-style struct initializer is not allowed in C++. How can this be ported to C++?

typedef struct {
  char const *property;
  int count;
} TYPE2;

typedef struct {
  int Address;             
  char const *Name;         
  union
  {
    TYPE1 foo;
    TYPE2 bar;
  }u;
} PARAMS;

//Initialize table:
const PARAMS paramTbl[] =
{
  {0x1000, "Param 1", {.bar = {"abc",0}}}, //So on ..
  .
  . 
}

Any help appreciated.

Mohit Jain · Accepted Answer · 2015-06-11 07:06:18Z

2

You can have a struct/union constructor to initialize with given value.

struct PARAMS {
  PARAMS(int address, const char *name, const TYPE1 &f) :
                    Address(address), Name(name), u(f)
  {
  }
  PARAMS(int address, const char *name, const TYPE2 &b) :
                    Address(address), Name(name), u(b)
  {
  }

  int Address;
  char const *Name;         
  union union_name
  {
    union_name(const TYPE1 &f) : foo(f) {}
    union_name(const TYPE2 &b) : bar(b) {}
    TYPE1 foo;
    TYPE2 bar;
  }u;
};

const PARAMS paramTbl[] {
  PARAMS(0x1000, "Param1", TYPE1("abc", 0)),
};

Complete example here

edited Jun 11, 2015 at 7:06

answered Jun 11, 2015 at 6:13

Mohit Jain

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1 Comment

OnkarK Over a year ago

bar is inside a union u. I am unable to initialize it this way. Compiler is unable to resolve bar in ctor parameters.

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