C++ Initialize nested struct

Question

I'm feeling really dumb right now, because it's been almost 2 years since I've done any C/C++, while my job has had me writing Java for that time and now I'm having trouble remembering even simple stuff, or else I remember the way to do it in Java instead... I have some C code that I'm trying to use in C++, but I'm having issues with the few things that aren't directly compatible, like struct initialization. The struct definition looks like this:

typedef struct
{
    struct
    {
        uint8_t  StreamingInterfaceNumber;
        USB_Endpoint_Table_t DataINEndpoint;
        USB_Endpoint_Table_t DataOUTEndpoint;
    } Config;

    struct
    {
        uint8_t RESERVED;
    } State;
} USB_ClassInfo_MIDI_Device_t;

The original C-style initialization looks like this:

USB_ClassInfo_MIDI_Device_t MIDI_Interface =
{
    .Config =
        {
            .StreamingInterfaceNumber = 1,
            .DataINEndpoint           =
                {
                    .Address          = MIDI_STREAM_IN_EPNUM,
                    .Size             = MIDI_STREAM_EPSIZE,
                    .Banks            = 1,
                },
            .DataOUTEndpoint           =
                {
                    .Address          = MIDI_STREAM_OUT_EPNUM,
                    .Size             = MIDI_STREAM_EPSIZE,
                    .Banks            = 1,
                },
        },
};

Which obviously doesn't work in C++. What's the best way to initialize a struct in C++? I don't want to modify the definition, since it exists in a code library that I don't maintain, and would like to leave alone, so I'd rather not add a constructor. I like the style suggested here https://stackoverflow.com/a/6182627/1609411 but I don't know what the syntax is supposed to look like for the nested structs.

Xymostech · Accepted Answer · 2013-02-16 05:20:33Z

1

I'm pretty sure that the style in that linked answer just involves commenting out all of the .BLAH = sections. As long as you have all of the fields in the right order, it will initialize fine.

USB_ClassInfo_MIDI_Device_t MIDI_Interface =
{
    /* .Config = */
        {
          /* .StreamingInterfaceNumber = */ 1,
          /* .DataINEndpoint           = */
                {
                    /* .Address          = */ MIDI_STREAM_IN_EPNUM,
                    /* .Size             = */ MIDI_STREAM_EPSIZE,
                    /* .Banks            = */ 1,
                },
          /* .DataOUTEndpoint           = */
                {
                    /* .Address          = */ MIDI_STREAM_OUT_EPNUM,
                    /* .Size             = */ MIDI_STREAM_EPSIZE,
                    /* .Banks            = */ 1,
                },
        },
};

answered Feb 16, 2013 at 5:20

Xymostech

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5 Comments

qwertymodo Over a year ago

I tried that but it gives me a compiler error "redefinition of 'USB_ClassInfo_MIDI_Device_t Keyboard_MIDI_Interface'"

Xymostech Over a year ago

@qwertymodo Where is it giving you that error? That doesn't look like something in this code.

qwertymodo Over a year ago

I typed exactly what you had there, and the error is on the first line USB_ClassInfo_MIDI_Device_t Keyboard_MIDI_Interface = The error references the original definition of the struct type and seems to think I'm redefining it here instead of instantiating it >.<

qwertymodo Over a year ago

Hmm... maybe it's because I'm doing this in the global scope?

borisbn Over a year ago

I think, it happens because you define variable MIDI_Interface in h-file and include it in more then one source. Move definition into cpp-file

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