Copy a std::vector to a repeated field from protobuf with memcpy

Question

At first I have this simple protobuf file

message messagetest
{
    ...
    repeated float samples = 6;
    ....
}

Which creates a headerfi

Answer 1

Since this isn't here yet and I like one-liners:

*fMessage.mutable_samples() = {fData.begin(), fData.end()};

Answer 2

I found the shortest way to copy vector into repeated field as this:

google::protobuf::RepeatedField<float> data(fData.begin(), fData.end());
fMessage.mutable_samples()->Swap(&data);

It is probably also faster than yours since it avoids initial iteration and setting values to 0.

Answer 3

fMessage.mutable_samples()

return an array of pointer of samples : [*sample1, *sample2, sample3, ...].

&fData[0]

is the address of first element of fData.

memcpy(fMessage.mutable_samples()->mutable_data(),
     &fData[0],
     sizeof(float)*fData.size());

So I do not think the code above can successfully fill data from fData to fMessage. It's totally wrong!