Passing byte array from c++ to c# (mono)

Question

I want to pass an array/vector/buffer of bytes from c++ to c#

On the c++ side I will have some data in a vector:

std::vector<unsigned char> pixels_cpp;

On the c# side I want to access these data in a byte array, e.g.

byte[] pixels_cs
// or as a MemoryStream object, accompanied with size information.

I am currently using this concept for passing strings from c++ to c#:

void MyWrapper::setSomeString(const std::string& someString)
{
    mono_thread_attach (mono_get_root_domain ());
    MonoMethod* mmSetSomeString = searchMethod("SetSomeString", monoClass);
    void *args [1];
    args [0] = mono_string_new (domain, someString.c_str());
    MonoObject *result = mono_runtime_invoke (mmSetSomeString, CsClassInstance, args, NULL);
    // check result
}

And the c# signature that is called is:

public bool SetSomeString(string someString)

How does this look like if I want to pass a vector of bytes?

How do I allocate the memory and fill it with data from pixels_cpp?
How to I invoke the call with mono_runtime_invoke (or equivalent)?
How should the c# method signature look like?

user3729611 · Accepted Answer · 2020-02-21 14:17:31Z

1

The solution is to use mono_array_new. Example:

void MyWrapper::setVector(std::vector<uint8_t>& data)
{
    mono_thread_attach (mono_get_root_domain ());
    MonoMethod* mmSetVector = searchMethod("SetVector", monoClass);

    void *args [1];
    MonoArray *data  = mono_array_new(domain, mono_get_byte_class(), data.size());

    for (auto i=0; i<data.size(); i++) {
        mono_array_set (data, uint8_t, i, data[i]);
    }

    args [0] = data;

    MonoObject *result = mono_runtime_invoke (mmSetVector, CsClassInstance, args, NULL);
    // check result
}

answered Feb 21, 2020 at 14:17

user3729611

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