Protocol Buffers

message.h

#include <google/protobuf/message.h>
namespace google::protobuf

Defines Message, the abstract interface implemented by non-lite protocol message objects.

Although it's possible to implement this interface manually, most users will use the protocol compiler to generate implementations.

Example usage:

Say you have a message defined as:

message Foo {
  optional string text = 1;
  repeated int32 numbers = 2;
}

Then, if you used the protocol compiler to generate a class from the above definition, you could use it like so:

string data;  // Will store a serialized version of the message.

{
 Create a message and serialize it.
  Foo foo;
  foo.set_text("Hello World!");
  foo.add_numbers(1);
  foo.add_numbers(5);
  foo.add_numbers(42);

  foo.SerializeToString(&data);
}

{
 Parse the serialized message and check that it contains the
 correct data.
  Foo foo;
  foo.ParseFromString(data);

  assert(foo.text() == "Hello World!");
  assert(foo.numbers_size() == 3);
  assert(foo.numbers(0) == 1);
  assert(foo.numbers(1) == 5);
  assert(foo.numbers(2) == 42);
}

{
 Same as the last block, but do it dynamically via the Message
 reflection interface.
  Message* foo = new Foo;
  const Descriptor* descriptor = foo->GetDescriptor();

 Get the descriptors for the fields we're interested in and verify
 their types.
  const FieldDescriptor* text_field = descriptor->FindFieldByName("text");
  assert(text_field != NULL);
  assert(text_field->type() == FieldDescriptor::TYPE_STRING);
  assert(text_field->label() == FieldDescriptor::LABEL_OPTIONAL);
  const FieldDescriptor* numbers_field = descriptor->
                                         FindFieldByName("numbers");
  assert(numbers_field != NULL);
  assert(numbers_field->type() == FieldDescriptor::TYPE_INT32);
  assert(numbers_field->label() == FieldDescriptor::LABEL_REPEATED);

 Parse the message.
  foo->ParseFromString(data);

 Use the reflection interface to examine the contents.
  const Reflection* reflection = foo->GetReflection();
  assert(reflection->GetString(foo, text_field) == "Hello World!");
  assert(reflection->FieldSize(foo, numbers_field) == 3);
  assert(reflection->GetRepeatedInt32(foo, numbers_field, 0) == 1);
  assert(reflection->GetRepeatedInt32(foo, numbers_field, 1) == 5);
  assert(reflection->GetRepeatedInt32(foo, numbers_field, 2) == 42);

  delete foo;
}

Classes in this file

A container to hold message metadata.
Abstract interface for protocol messages.
This interface contains methods that can be used to dynamically access and modify the fields of a protocol message.
Abstract interface for a factory for message objects.

struct Metadata

#include <google/protobuf/message.h>
namespace google::protobuf

A container to hold message metadata.

Members

const Descriptor *
descriptor
const Reflection *
reflection

class Message: public MessageLite

#include <google/protobuf/message.h>
namespace google::protobuf

Abstract interface for protocol messages.

See also MessageLite, which contains most every-day operations. Message adds descriptors and reflection on top of that.

The methods of this class that are virtual but not pure-virtual have default implementations based on reflection. Message classes which are optimized for speed will want to override these with faster implementations, but classes optimized for code size may be happy with keeping them. See the optimize_for option in descriptor.proto.

Known subclasses:

Members

Message()
virtual
~Message()
string
DebugString() const
Generates a human readable form of this message, useful for debugging and other purposes.
string
ShortDebugString() const
Like DebugString(), but with less whitespace.
string
Utf8DebugString() const
Like DebugString(), but do not escape UTF-8 byte sequences.
void
PrintDebugString() const
Convenience function useful in GDB. Prints DebugString() to stdout.
bool
ParseFromFileDescriptor(int file_descriptor)
Parse a protocol buffer from a file descriptor. more...
bool
ParsePartialFromFileDescriptor(int file_descriptor)
Like ParseFromFileDescriptor(), but accepts messages that are missing required fields.
bool
ParseFromIstream(istream * input)
Parse a protocol buffer from a C++ istream. more...
bool
ParsePartialFromIstream(istream * input)
Like ParseFromIstream(), but accepts messages that are missing required fields.
bool
SerializeToFileDescriptor(int file_descriptor) const
Serialize the message and write it to the given file descriptor. more...
bool
SerializePartialToFileDescriptor(int file_descriptor) const
Like SerializeToFileDescriptor(), but allows missing required fields.
bool
SerializeToOstream(ostream * output) const
Serialize the message and write it to the given C++ ostream. more...
bool
SerializePartialToOstream(ostream * output) const
Like SerializeToOstream(), but allows missing required fields.
virtual string
GetTypeName() const
Get the name of this message type, e.g. "foo.bar.BazProto".
virtual void
Clear()
Clear all fields of the message and set them to their default values. more...
virtual bool
IsInitialized() const
Quickly check if all required fields have values set.
virtual void
CheckTypeAndMergeFrom(const MessageLite & other)
If |other| is the exact same class as this, calls MergeFrom(). more...
virtual bool
MergePartialFromCodedStream(io::CodedInputStream * input)
Like MergeFromCodedStream(), but succeeds even if required fields are missing in the input. more...
virtual int
ByteSize() const
Computes the serialized size of the message. more...
virtual void
SerializeWithCachedSizes(io::CodedOutputStream * output) const
Serializes the message without recomputing the size. more...
protected virtual Metadata
GetMetadata() const = 0
Get a struct containing the metadata for the Message. more...

Basic Operations

virtual Message *
New() const = 0
Construct a new instance of the same type. more...
virtual void
CopyFrom(const Message & from)
Make this message into a copy of the given message. more...
virtual void
MergeFrom(const Message & from)
Merge the fields from the given message into this message. more...
void
CheckInitialized() const
Verifies that IsInitialized() returns true. more...
void
FindInitializationErrors(vector< string > * errors) const
Slowly build a list of all required fields that are not set. more...
virtual string
InitializationErrorString() const
Like FindInitializationErrors, but joins all the strings, delimited by commas, and returns them.
virtual void
DiscardUnknownFields()
Clears all unknown fields from this message and all embedded messages. more...
virtual int
SpaceUsed() const
Computes (an estimate of) the total number of bytes currently used for storing the message in memory. more...

Introspection

typedef
Typedef for backwards-compatibility.
const Descriptor *
GetDescriptor() const
Get a Descriptor for this message's type. more...
virtual const Reflection *
GetReflection() const
Get the Reflection interface for this Message, which can be used to read and modify the fields of the Message dynamically (in other words, without knowing the message type at compile time). more...

bool Message::ParseFromFileDescriptor(
        int file_descriptor)

Parse a protocol buffer from a file descriptor.

If successful, the entire input will be consumed.


bool Message::ParseFromIstream(
        istream * input)

Parse a protocol buffer from a C++ istream.

If successful, the entire input will be consumed.


bool Message::SerializeToFileDescriptor(
        int file_descriptor) const

Serialize the message and write it to the given file descriptor.

All required fields must be set.


bool Message::SerializeToOstream(
        ostream * output) const

Serialize the message and write it to the given C++ ostream.

All required fields must be set.


virtual void Message::Clear()

Clear all fields of the message and set them to their default values.

Clear() avoids freeing memory, assuming that any memory allocated to hold parts of the message will be needed again to hold the next message. If you actually want to free the memory used by a Message, you must delete it.


virtual void Message::CheckTypeAndMergeFrom(
        const MessageLite & other)

If |other| is the exact same class as this, calls MergeFrom().

Otherwise, results are undefined (probably crash).


virtual bool Message::MergePartialFromCodedStream(
        io::CodedInputStream * input)

Like MergeFromCodedStream(), but succeeds even if required fields are missing in the input.

MergeFromCodedStream() is just implemented as MergePartialFromCodedStream() followed by IsInitialized().


virtual int Message::ByteSize() const

Computes the serialized size of the message.

This recursively calls ByteSize() on all embedded messages. If a subclass does not override this, it MUST override SetCachedSize().


virtual void Message::SerializeWithCachedSizes(
        io::CodedOutputStream * output) const

Serializes the message without recomputing the size.

The message must not have changed since the last call to ByteSize(); if it has, the results are undefined.


protected virtual Metadata Message::GetMetadata() const = 0

Get a struct containing the metadata for the Message.

Most subclasses only need to implement this method, rather than the GetDescriptor() and GetReflection() wrappers.


virtual Message * Message::New() const = 0

Construct a new instance of the same type.

Ownership is passed to the caller. (This is also defined in MessageLite, but is defined again here for return-type covariance.)


virtual void Message::CopyFrom(
        const Message & from)

Make this message into a copy of the given message.

The given message must have the same descriptor, but need not necessarily be the same class. By default this is just implemented as "Clear(); MergeFrom(from);".


virtual void Message::MergeFrom(
        const Message & from)

Merge the fields from the given message into this message.

Singular fields will be overwritten, except for embedded messages which will be merged. Repeated fields will be concatenated. The given message must be of the same type as this message (i.e. the exact same class).


void Message::CheckInitialized() const

Verifies that IsInitialized() returns true.

GOOGLE_CHECK-fails otherwise, with a nice error message.


void Message::FindInitializationErrors(
        vector< string > * errors) const

Slowly build a list of all required fields that are not set.

This is much, much slower than IsInitialized() as it is implemented purely via reflection. Generally, you should not call this unless you have already determined that an error exists by calling IsInitialized().


virtual void Message::DiscardUnknownFields()

Clears all unknown fields from this message and all embedded messages.

Normally, if unknown tag numbers are encountered when parsing a message, the tag and value are stored in the message's UnknownFieldSet and then written back out when the message is serialized. This allows servers which simply route messages to other servers to pass through messages that have new field definitions which they don't yet know about. However, this behavior can have security implications. To avoid it, call this method after parsing.

See Reflection::GetUnknownFields() for more on unknown fields.


virtual int Message::SpaceUsed() const

Computes (an estimate of) the total number of bytes currently used for storing the message in memory.

The default implementation calls the Reflection object's SpaceUsed() method.


const Descriptor *
    Message::GetDescriptor() const

Get a Descriptor for this message's type.

This describes what fields the message contains, the types of those fields, etc.


virtual const Reflection *
    Message::GetReflection() const

Get the Reflection interface for this Message, which can be used to read and modify the fields of the Message dynamically (in other words, without knowing the message type at compile time).

This object remains property of the Message.

This method remains virtual in case a subclass does not implement reflection and wants to override the default behavior.

class Reflection

#include <google/protobuf/message.h>
namespace google::protobuf

This interface contains methods that can be used to dynamically access and modify the fields of a protocol message.

Their semantics are similar to the accessors the protocol compiler generates.

To get the Reflection for a given Message, call Message::GetReflection().

This interface is separate from Message only for efficiency reasons; the vast majority of implementations of Message will share the same implementation of Reflection (GeneratedMessageReflection, defined in generated_message.h), and all Messages of a particular class should share the same Reflection object (though you should not rely on the latter fact).

There are several ways that these methods can be used incorrectly. For example, any of the following conditions will lead to undefined results (probably assertion failures):

  • The FieldDescriptor is not a field of this message type.
  • The method called is not appropriate for the field's type. For each field type in FieldDescriptor::TYPE_*, there is only one Get*() method, one Set*() method, and one Add*() method that is valid for that type. It should be obvious which (except maybe for TYPE_BYTES, which are represented using strings in C++).
  • A Get*() or Set*() method for singular fields is called on a repeated field.
  • GetRepeated*(), SetRepeated*(), or Add*() is called on a non-repeated field.
  • The Message object passed to any method is not of the right type for this Reflection object (i.e. message.GetReflection() != reflection).

You might wonder why there is not any abstract representation for a field of arbitrary type. E.g., why isn't there just a "GetField()" method that returns "const Field&", where "Field" is some class with accessors like "GetInt32Value()". The problem is that someone would have to deal with allocating these Field objects. For generated message classes, having to allocate space for an additional object to wrap every field would at least double the message's memory footprint, probably worse. Allocating the objects on-demand, on the other hand, would be expensive and prone to memory leaks. So, instead we ended up with this flat interface.

TODO(kenton): Create a utility class which callers can use to read and write fields from a Reflection without paying attention to the type.

Members

Reflection()
virtual
~Reflection()
virtual const UnknownFieldSet &
GetUnknownFields(const Message & message) const = 0
Get the UnknownFieldSet for the message. more...
virtual UnknownFieldSet *
MutableUnknownFields(Message * message) const = 0
Get a mutable pointer to the UnknownFieldSet for the message. more...
virtual int
SpaceUsed(const Message & message) const = 0
Estimate the amount of memory used by the message object.
virtual bool
HasField(const Message & message, const FieldDescriptor * field) const = 0
Check if the given non-repeated field is set.
virtual int
FieldSize(const Message & message, const FieldDescriptor * field) const = 0
Get the number of elements of a repeated field.
virtual void
ClearField(Message * message, const FieldDescriptor * field) const = 0
Clear the value of a field, so that HasField() returns false or FieldSize() returns zero.
virtual void
RemoveLast(Message * message, const FieldDescriptor * field) const = 0
Removes the last element of a repeated field. more...
virtual Message *
ReleaseLast(Message * message, const FieldDescriptor * field) const = 0
Removes the last element of a repeated message field, and returns the pointer to the caller. more...
virtual void
Swap(Message * message1, Message * message2) const = 0
Swap the complete contents of two messages.
virtual void
SwapElements(Message * message, const FieldDescriptor * field, int index1, int index2) const = 0
Swap two elements of a repeated field.
virtual void
ListFields(const Message & message, vector< const FieldDescriptor * > * output) const = 0
List all fields of the message which are currently set. more...
virtual void
SetInt32(Message * message, const FieldDescriptor * field, int32 value) const = 0
virtual void
SetInt64(Message * message, const FieldDescriptor * field, int64 value) const = 0
virtual void
SetUInt32(Message * message, const FieldDescriptor * field, uint32 value) const = 0
virtual void
SetUInt64(Message * message, const FieldDescriptor * field, uint64 value) const = 0
virtual void
SetFloat(Message * message, const FieldDescriptor * field, float value) const = 0
virtual void
SetDouble(Message * message, const FieldDescriptor * field, double value) const = 0
virtual void
SetBool(Message * message, const FieldDescriptor * field, bool value) const = 0
virtual void
SetString(Message * message, const FieldDescriptor * field, const string & value) const = 0
virtual void
SetEnum(Message * message, const FieldDescriptor * field, const EnumValueDescriptor * value) const = 0
virtual Message *
MutableMessage(Message * message, const FieldDescriptor * field, MessageFactory * factory = NULL) const = 0
Get a mutable pointer to a field with a message type. more...
virtual Message *
ReleaseMessage(Message * message, const FieldDescriptor * field, MessageFactory * factory = NULL) const = 0
Releases the message specified by 'field' and returns the pointer, ReleaseMessage() will return the message the message object if it exists. more...
virtual int32
GetRepeatedInt32(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual int64
GetRepeatedInt64(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual uint32
GetRepeatedUInt32(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual uint64
GetRepeatedUInt64(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual float
GetRepeatedFloat(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual double
GetRepeatedDouble(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual bool
GetRepeatedBool(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual string
GetRepeatedString(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual const EnumValueDescriptor *
GetRepeatedEnum(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual const Message &
GetRepeatedMessage(const Message & message, const FieldDescriptor * field, int index) const = 0
virtual const string &
GetRepeatedStringReference(const Message & message, const FieldDescriptor * field, int index, string * scratch) const = 0
virtual void
SetRepeatedInt32(Message * message, const FieldDescriptor * field, int index, int32 value) const = 0
virtual void
SetRepeatedInt64(Message * message, const FieldDescriptor * field, int index, int64 value) const = 0
virtual void
SetRepeatedUInt32(Message * message, const FieldDescriptor * field, int index, uint32 value) const = 0
virtual void
SetRepeatedUInt64(Message * message, const FieldDescriptor * field, int index, uint64 value) const = 0
virtual void
SetRepeatedFloat(Message * message, const FieldDescriptor * field, int index, float value) const = 0
virtual void
SetRepeatedDouble(Message * message, const FieldDescriptor * field, int index, double value) const = 0
virtual void
SetRepeatedBool(Message * message, const FieldDescriptor * field, int index, bool value) const = 0
virtual void
SetRepeatedString(Message * message, const FieldDescriptor * field, int index, const string & value) const = 0
virtual void
SetRepeatedEnum(Message * message, const FieldDescriptor * field, int index, const EnumValueDescriptor * value) const = 0
virtual Message *
MutableRepeatedMessage(Message * message, const FieldDescriptor * field, int index) const = 0
Get a mutable pointer to an element of a repeated field with a message type.
virtual void
AddInt32(Message * message, const FieldDescriptor * field, int32 value) const = 0
virtual void
AddInt64(Message * message, const FieldDescriptor * field, int64 value) const = 0
virtual void
AddUInt32(Message * message, const FieldDescriptor * field, uint32 value) const = 0
virtual void
AddUInt64(Message * message, const FieldDescriptor * field, uint64 value) const = 0
virtual void
AddFloat(Message * message, const FieldDescriptor * field, float value) const = 0
virtual void
AddDouble(Message * message, const FieldDescriptor * field, double value) const = 0
virtual void
AddBool(Message * message, const FieldDescriptor * field, bool value) const = 0
virtual void
AddString(Message * message, const FieldDescriptor * field, const string & value) const = 0
virtual void
AddEnum(Message * message, const FieldDescriptor * field, const EnumValueDescriptor * value) const = 0
virtual Message *
AddMessage(Message * message, const FieldDescriptor * field, MessageFactory * factory = NULL) const = 0
See MutableMessage() for comments on the "factory" parameter.
virtual const FieldDescriptor *
FindKnownExtensionByName(const string & name) const = 0
Try to find an extension of this message type by fully-qualified field name. more...
virtual const FieldDescriptor *
FindKnownExtensionByNumber(int number) const = 0
Try to find an extension of this message type by field number. more...
protected virtual void *
MutableRawRepeatedField(Message * message, const FieldDescriptor * field, FieldDescriptor::CppType , int ctype, const Descriptor * message_type) const = 0
Obtain a pointer to a Repeated Field Structure and do some type checking: more...

Singular field getters

These get the value of a non-repeated field. They return the default value for fields that aren't set.
virtual int32
GetInt32(const Message & message, const FieldDescriptor * field) const = 0
virtual int64
GetInt64(const Message & message, const FieldDescriptor * field) const = 0
virtual uint32
GetUInt32(const Message & message, const FieldDescriptor * field) const = 0
virtual uint64
GetUInt64(const Message & message, const FieldDescriptor * field) const = 0
virtual float
GetFloat(const Message & message, const FieldDescriptor * field) const = 0
virtual double
GetDouble(const Message & message, const FieldDescriptor * field) const = 0
virtual bool
GetBool(const Message & message, const FieldDescriptor * field) const = 0
virtual string
GetString(const Message & message, const FieldDescriptor * field) const = 0
virtual const EnumValueDescriptor *
GetEnum(const Message & message, const FieldDescriptor * field) const = 0
virtual const Message &
GetMessage(const Message & message, const FieldDescriptor * field, MessageFactory * factory = NULL) const = 0
See MutableMessage() for the meaning of the "factory" parameter.
virtual const string &
GetStringReference(const Message & message, const FieldDescriptor * field, string * scratch) const = 0
Get a string value without copying, if possible. more...

Repeated field accessors

The methods above, e.g.

GetRepeatedInt32(msg, fd, index), provide singular access to the data in a RepeatedField. The methods below provide aggregate access by exposing the RepeatedField object itself with the Message. Applying these templates to inappropriate types will lead to an undefined reference at link time (e.g. GetRepeatedField<***double>), or possibly a template matching error at compile time (e.g. GetRepeatedPtrField<File>).

Usage example: my_doubs = refl->GetRepeatedField<double>(msg, fd);

template const RepeatedField< T > &
GetRepeatedField(const Message & , const FieldDescriptor * ) const
for T = Cord and all protobuf scalar types except enums.
template RepeatedField< T > *
MutableRepeatedField(Message * , const FieldDescriptor * ) const
for T = Cord and all protobuf scalar types except enums.
template const RepeatedPtrField< T > &
GetRepeatedPtrField(const Message & , const FieldDescriptor * ) const
for T = string, google::protobuf::internal::StringPieceField more...
template RepeatedPtrField< T > *
MutableRepeatedPtrField(Message * , const FieldDescriptor * ) const
for T = string, google::protobuf::internal::StringPieceField more...

virtual const UnknownFieldSet &
    Reflection::GetUnknownFields(
        const Message & message) const = 0

Get the UnknownFieldSet for the message.

This contains fields which were seen when the Message was parsed but were not recognized according to the Message's definition.


virtual UnknownFieldSet *
    Reflection::MutableUnknownFields(
        Message * message) const = 0

Get a mutable pointer to the UnknownFieldSet for the message.

This contains fields which were seen when the Message was parsed but were not recognized according to the Message's definition.


virtual void Reflection::RemoveLast(
        Message * message,
        const FieldDescriptor * field) const = 0

Removes the last element of a repeated field.

We don't provide a way to remove any element other than the last because it invites inefficient use, such as O(n^2) filtering loops that should have been O(n). If you want to remove an element other than the last, the best way to do it is to re-arrange the elements (using Swap()) so that the one you want removed is at the end, then call RemoveLast().


virtual Message * Reflection::ReleaseLast(
        Message * message,
        const FieldDescriptor * field) const = 0

Removes the last element of a repeated message field, and returns the pointer to the caller.

Caller takes ownership of the returned pointer.


virtual void Reflection::ListFields(
        const Message & message,
        vector< const FieldDescriptor * > * output) const = 0

List all fields of the message which are currently set.

This includes extensions. Singular fields will only be listed if HasField(field) would return true and repeated fields will only be listed if FieldSize(field) would return non-zero. Fields (both normal fields and extension fields) will be listed ordered by field number.


virtual Message * Reflection::MutableMessage(
        Message * message,
        const FieldDescriptor * field,
        MessageFactory * factory = NULL) const = 0

Get a mutable pointer to a field with a message type.

If a MessageFactory is provided, it will be used to construct instances of the sub-message; otherwise, the default factory is used. If the field is an extension that does not live in the same pool as the containing message's descriptor (e.g. it lives in an overlay pool), then a MessageFactory must be provided. If you have no idea what that meant, then you probably don't need to worry about it (don't provide a MessageFactory). WARNING: If the FieldDescriptor is for a compiled-in extension, then factory->GetPrototype(field->message_type() MUST return an instance of the compiled-in class for this type, NOT DynamicMessage.


virtual Message * Reflection::ReleaseMessage(
        Message * message,
        const FieldDescriptor * field,
        MessageFactory * factory = NULL) const = 0

Releases the message specified by 'field' and returns the pointer, ReleaseMessage() will return the message the message object if it exists.

Otherwise, it may or may not return NULL. In any case, if the return value is non-NULL, the caller takes ownership of the pointer. If the field existed (HasField() is true), then the returned pointer will be the same as the pointer returned by MutableMessage(). This function has the same effect as ClearField().


virtual const FieldDescriptor *
    Reflection::FindKnownExtensionByName(
        const string & name) const = 0

Try to find an extension of this message type by fully-qualified field name.

Returns NULL if no extension is known for this name or number.


virtual const FieldDescriptor *
    Reflection::FindKnownExtensionByNumber(
        int number) const = 0

Try to find an extension of this message type by field number.

Returns NULL if no extension is known for this name or number.


protected virtual void * Reflection::MutableRawRepeatedField(
        Message * message,
        const FieldDescriptor * field,
        FieldDescriptor::CppType ,
        int ctype,
        const Descriptor * message_type) const = 0

Obtain a pointer to a Repeated Field Structure and do some type checking:

on field->cpp_type(),
on field->field_option().ctype() (if ctype >= 0)
of field->message_type() (if message_type != NULL).

We use 1 routine rather than 4 (const vs mutable) x (scalar vs pointer).


virtual const string & Reflection::GetStringReference(
        const Message & message,
        const FieldDescriptor * field,
        string * scratch) const = 0

Get a string value without copying, if possible.

GetString() necessarily returns a copy of the string. This can be inefficient when the string is already stored in a string object in the underlying message. GetStringReference() will return a reference to the underlying string in this case. Otherwise, it will copy the string into scratch and return that.

Note: It is perfectly reasonable and useful to write code like:

str = reflection->GetStringReference(field, &str);

This line would ensure that only one copy of the string is made regardless of the field's underlying representation. When initializing a newly-constructed string, though, it's just as fast and more readable to use code like:

string str = reflection->GetString(field);

template const RepeatedPtrField< T > &
    Reflection::GetRepeatedPtrField(
        const Message & ,
        const FieldDescriptor * ) const

for T = string, google::protobuf::internal::StringPieceField

    google::protobuf::Message & descendants.

template RepeatedPtrField< T > *
    Reflection::MutableRepeatedPtrField(
        Message * ,
        const FieldDescriptor * ) const

for T = string, google::protobuf::internal::StringPieceField

    google::protobuf::Message & descendants.

class MessageFactory

#include <google/protobuf/message.h>
namespace google::protobuf

Abstract interface for a factory for message objects.

Known subclasses:

Members

MessageFactory()
virtual
~MessageFactory()
virtual const Message *
GetPrototype(const Descriptor * type) = 0
Given a Descriptor, gets or constructs the default (prototype) Message of that type. more...
static MessageFactory *
generated_factory()
Gets a MessageFactory which supports all generated, compiled-in messages. more...
static void
InternalRegisterGeneratedFile(const char * filename, void(*)(const string &) register_messages)
For internal use only: Registers a .proto file at static initialization time, to be placed in generated_factory. more...
static void
InternalRegisterGeneratedMessage(const Descriptor * descriptor, const Message * prototype)
For internal use only: Registers a message type. more...

virtual const Message * MessageFactory::GetPrototype(
        const Descriptor * type) = 0

Given a Descriptor, gets or constructs the default (prototype) Message of that type.

You can then call that message's New() method to construct a mutable message of that type.

Calling this method twice with the same Descriptor returns the same object. The returned object remains property of the factory. Also, any objects created by calling the prototype's New() method share some data with the prototype, so these must be destoyed before the MessageFactory is destroyed.

The given descriptor must outlive the returned message, and hence must outlive the MessageFactory.

Some implementations do not support all types. GetPrototype() will return NULL if the descriptor passed in is not supported.

This method may or may not be thread-safe depending on the implementation. Each implementation should document its own degree thread-safety.


static MessageFactory * MessageFactory::generated_factory()

Gets a MessageFactory which supports all generated, compiled-in messages.

In other words, for any compiled-in type FooMessage, the following is true:

MessageFactory::generated_factory()->GetPrototype(
  FooMessage::descriptor()) == FooMessage::default_instance()

This factory supports all types which are found in DescriptorPool::generated_pool(). If given a descriptor from any other pool, GetPrototype() will return NULL. (You can also check if a descriptor is for a generated message by checking if descriptor->file()->pool() == DescriptorPool::generated_pool().)

This factory is 100% thread-safe; calling GetPrototype() does not modify any shared data.

This factory is a singleton. The caller must not delete the object.


static void MessageFactory::InternalRegisterGeneratedFile(
        const char * filename,
        void(*)(const string &) register_messages)

For internal use only: Registers a .proto file at static initialization time, to be placed in generated_factory.

The first time GetPrototype() is called with a descriptor from this file, |register_messages| will be called, with the file name as the parameter. It must call InternalRegisterGeneratedMessage() (below) to register each message type in the file. This strange mechanism is necessary because descriptors are built lazily, so we can't register types by their descriptor until we know that the descriptor exists. |filename| must be a permanent string.


static void MessageFactory::InternalRegisterGeneratedMessage(
        const Descriptor * descriptor,
        const Message * prototype)

For internal use only: Registers a message type.

Called only by the functions which are registered with InternalRegisterGeneratedFile(), above.

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