C/C++ struct in C# via P/Invoke

Question

I am taking my first steps using P/Invoke and try to represent these C/C++ structs:

#ifndef struct_emxArray_char_T_1024
#define struct_emxArray_char_T_1024
struct emxArray_char_T_1024
{
    char_T data[1024];
    int32_T size[1];
};

#ifndef typedef_e_struct_T
#define typedef_e_struct_T
typedef struct
{
    emxArray_char_T_1024 value1;
    real_T value2;
    uint32_T value3;
    boolean_T value4;
} e_struct_T;

using this in C#:

[StructLayout(LayoutKind.Sequential)]
class emxArray_char_T_1024
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 1024)]
    public string data;
    [In, MarshalAs(UnmanagedType.I4)]
    public int size;
}

StructLayout(LayoutKind.Sequential)]
class e_struct_T
{
    emxArray_char_T_1024 value1;
    double value2;
    uint value3;
    bool value4;
}

Does this look sufficient? I am not too sure about the comments like this in the tutorial:

compile with: /target:module

PS:

The above 'types' seem to be defined like this:

typedef double real_T;
typedef unsigned int uint32_T;
typedef unsigned char boolean_T;
typedef char char_T;
typedef int int32_T;

Just to start: how real_T is defined? float or double? boolean_T? byte or int? char_T? wchar_t or char? — Adriano Repetti
– Adriano Repetti, Commented Dec 2, 2012 at 10:35
Thanks Adriano. Did not realize that these 'types' are not common. Had a look in the header files and found the stuff in PS (see edited question). — cs0815
– cs0815, Commented Dec 2, 2012 at 10:44
OK, System.Boolean is 4 bytes so it has be decorared with MarshalAs. Everything else looks OK to me. — Adriano Repetti
– Adriano Repetti, Commented Dec 2, 2012 at 10:45
Thanks. Would you mind posting an answer then with the correct attribute for Boolean please? — cs0815
– cs0815, Commented Dec 2, 2012 at 10:53

Adriano Repetti · Accepted Answer · 2012-12-02 11:34:17Z

1

Final struct looks OK to me, the only change you should do is how your boolean_T is marshaled. Default C-style bool is one byte signed integer so it must be marshaled as I1. You declared boolean_T it as unsigned char so it should be U1:

[StructLayout(LayoutKind.Sequential)]
class e_struct_T
{
    emxArray_char_T_1024 value1;
    double value2;
    uint value3;

    [MarshalAs(UnmanagedType.U1)] 
    bool value4;
}

edited Dec 2, 2012 at 11:34

answered Dec 2, 2012 at 11:24

Adriano Repetti

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4 Comments

cs0815 Over a year ago

I am having a closer look at this. value2 seems to be always zero. Maybe it is too naive to assume that I can just use double for real_T? Thanks.

Adriano Repetti Over a year ago

No, it should be OK. Try to replace value2 with, for example, an int to check what you get there. It may be a disalignment of the other struct.

cs0815 Over a year ago

Mmmh, just looking at emxArray_char_T_1024. Is int32_T size[1] -> [In, MarshalAs(UnmanagedType.I4)] public int size actaully correct?

Adriano Repetti Over a year ago

By chance I thought it could be, can you try with [MarshalAs(UnmanagedType.ByValArray, SizeConst=1)] public int[] size?

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