How can I initialize an array of struct with array?

Question

I have the following code but I am having problem to initialize. How can I initialize an array of struct with array?

typedef struct
{
    UINT8_T ID;
    string CN;
} CU_ContractDesc;

typedef struct
{
    UINT8_T DataType;
    UINT8_T DataSize;
    string SignalName; //This used only for debugging
    UINT8_T NrCont;
    CU_ContractDesc Contracts [];
} CU_BusDesc;

CU_BusDesc BusItems[]={
     {SS_SINGLE, sizeof(single_T), "S1", 1, {{99, "GV1"}}},
     {SS_UINT32, sizeof(uint32_T), "S2", 1, {{99, "GV1"}, {1, "GV2"}}}
};

Plain arrays in C++ are dumb: CU_ContractDesc Contracts[]; has to have a fixed size (e.g. CU_ContractDesc Contracts[4];). Since that is probably not what you want, use std::vector<CU_ContractDesc> Contracts; instead. — HolyBlackCat
– HolyBlackCat, Commented Mar 6, 2020 at 9:51
It would be useful to know how the different types are defined. — Johan
– Johan, Commented Mar 6, 2020 at 9:51
AFAIR, c++ does not allow member variables with incomplete type, not even at the end of a struct. — Johan
– Johan, Commented Mar 6, 2020 at 10:01

Alan Birtles · Accepted Answer · 2020-03-06 10:04:39Z

If your array size is fixed you must specify its size:

struct CU_BusDesc
{
    UINT8_T DataType;
    UINT8_T DataSize;
    string SignalName; //This used only for debugging
    UINT8_T NrCont;
    CU_ContractDesc Contracts [2];
};

or

struct CU_BusDesc
{
    UINT8_T DataType;
    UINT8_T DataSize;
    string SignalName; //This used only for debugging
    UINT8_T NrCont;
    std::array<CU_ContractDesc, 2> Contracts;
};

CU_BusDesc BusItems[]={
     {SS_SINGLE, sizeof(single_T), "S1", 1, {{{99, "GV1"}}}},
     {SS_UINT32, sizeof(uint32_T), "S2", 1, {{{99, "GV1"}, {1, "GV2"}}}}
};

note that additional braces are required for the std::array initialisation.

If the array isn't a fixed size you should use std::vector, c++ doesn't support structures with arrays with unspecified sizes:

struct CU_BusDesc
{
    UINT8_T DataType;
    UINT8_T DataSize;
    string SignalName; //This used only for debugging
    UINT8_T NrCont;
    std::vector<CU_ContractDesc> Contracts;
};

This will work with your original initialisers.

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