How do I read a .proto formatted binary file in C++?

Question

I have a .bin file created using C# with a protobuf library and the following class:

[ProtoContract]
class TextureAtlasEntry
{
    [ProtoMember(1)]
    public int Height { get; set; }

    [ProtoMember(2)]
    public string Name { get; set; }

    [ProtoMember(3)]
    public int Width { get; set; }

    [ProtoMember(4)]
    public int X { get; set; }

    [ProtoMember(5)]
    public int Y { get; set; }
}

The associated .proto file looks like

package TextureAtlasSettings;           // Namespace equivalent

message TextureAtlasEntry               
{
    required int32 Height = 1;
    required string Name = 2;
    required int32 Width = 3;
    required int32 X = 4;
    required int32 Y = 5;
}

Which has been parsed through protoc.exe to produce TextureAtlasSettings.pb.cc and TextureAtlasSettings.pb.h. for C++.

I would like to read the resultant binary file in C++, so I tried the following code

TextureAtlasSettings::TextureAtlasEntry taSettings;

ifstream::pos_type size;
char *memblock;

ifstream file("Content\\Protobuf\\TextureAtlas0.bin", ios::in | ios::binary);

if (file.is_open())
{
    size = file.tellg();
    memblock = new char[size];
    file.seekg(0, ios::beg);
    file.read(memblock, size);
    file.close();

    fstream input(&memblock[0], ios::in | ios::binary);

    if (!taSettings.ParseFromIstream(&file)) 
    {
        printf("Failed to parse TextureAtlasEntry");
    }

    delete[] memblock;
}

The code above will always trigger the printf. How do I go about reading the file correctly so it may be deserialized?

Answer 1

The model you show actually represents, to protobuf-net, optional fields (several with a default of zero). Consequently, any zeros might be omitted, which would cause the c++ reader to reject the message (since your .proto lists it as required).

To get the representative .proto:

string proto = Serializer.GetProto<YourType>();

Or to make them "required" in the c#:

[ProtoMember(3, IsRequired = true)]

(etc)

Answer 2

It should be sufficient to do this:

TextureAtlasSettings::TextureAtlasEntry taSettings;

ifstream file("Content\\Protobuf\\TextureAtlas0.bin", ios::in | ios::binary);

if (file.is_open())
{
    if (!taSettings.ParseFromIstream(&file)) 
    {
        printf("Failed to parse TextureAtlasEntry");
    }
}