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c++cinitializationunionsc++03

Union initialization in C++ and C

I have built a working C library, that uses constants, in header files defined as

typedef struct Y {
  union {
    struct bit_field bits;
    uint8_t raw[4];
  } X;
} CardInfo;

static const CardInfo Y_CONSTANT = { .raw = {0, 0, 0, 0 } };

I know that the .raw initializer is C only syntax.

How do I define constants with unions in them in a way such that I can use them in C and C++.

Solution

  • I had the same problem. For C89 the following is true:

    With C89-style initializers, structure members must be initialized in the order declared, and only the first member of a union can be initialized

    I found this explanation at: Initialization of structures and unions