Question

protocol buffer say it can contain any arbitrary sequence of bytes. but if my data contain ‘\0’ ,how protocol buffer can encode my whole data from a string variable.

Answer 1

The C++ implementation of protocol buffers returns the byte and string types as std::string. This structure contains a length function telling you how long the corresponding data is (as well as the data itself.) Thus there is no special significance of embeded \0 characters.

The setting functions accept a string too, or there are versions that accept a buffer and length.
If you want to set a field you can just do this:

pb.set_foo( std::string( data, data_length ) );

or

pb.set_foo( data, data_length );