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Revamping the FlatBuffers docs.

Browse Source 
Adding an API reference for the supported languages.

General docs cleanup, including a new `tutorial` section that
supports all of the supported languages.

Added samples for each supported language to mirror the new
tutorial page.

Cleaned up all the links by making them `@ref` style links,
instead of referencing the names of the generated `.html` files.

Removed all generated files that were unnecessarily committed.

Also fixed the C# tests (two were failing due to a missing file).

Bug: b/25801305

Tested: Tested all samples on Ubuntu, Mac, and Android. Docs were
generated using doxygen and viewed on Chrome.

Change-Id: I2acaba6e332a15ae2deff5f26a4a25da7bd2c954
This commit is contained in:
Mark Klara
2015-12-03 20:30:54 -08:00
parent d75d29e2fe
commit 69a31b807a
115 changed files with 5537 additions and 5917 deletions
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docs/source/CppUsage.md
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@@ -1,227 +1,100 @@
# Use in C++
Use in C++ {#flatbuffers_guide_use_cpp}
==========
Assuming you have written a schema using the above language in say
`mygame.fbs` (FlatBuffer Schema, though the extension doesn't matter),
you've generated a C++ header called `mygame_generated.h` using the
## Before you get started
Before diving into the FlatBuffers usage in C++, it should be noted that
the [Tutorial](@ref flatbuffers_guide_tutorial) page has a complete guide
to general FlatBuffers usage in all of the supported languages (including C++).
This page is designed to cover the nuances of FlatBuffers usage, specific to
C++.
#### Prerequisites
This page assumes you have written a FlatBuffers schema and compiled it
with the Schema Compiler. If you have not, please see
[Using the schema compiler](@ref flatbuffers_guide_using_schema_compiler)
and [Writing a schema](@ref flatbuffers_guide_writing_schema).
Assuming you wrote a schema, say `mygame.fbs` (though the extension doesn't
matter), you've generated a C++ header called `mygame_generated.h` using the
compiler (e.g. `flatc -c mygame.fbs`), you can now start using this in
your program by including the header. As noted, this header relies on
`flatbuffers/flatbuffers.h`, which should be in your include path.
### Writing in C++
## FlatBuffers C++ library code location
To start creating a buffer, create an instance of `FlatBufferBuilder`
which will contain the buffer as it grows:
The code for the FlatBuffers C++ library can be found at
`flatbuffers/include/flatbuffers`. You can browse the library code on the
[FlatBuffers GitHub page](https://github.com/google/flatbuffers/tree/master/
include/flatbuffers).
## Testing the FlatBuffers C++ library
The code to test the C++ library can be found at `flatbuffers/tests`.
The test code itself is located in
[test.cpp](https://github.com/google/flatbuffers/blob/master/tests/test.cpp).
This test file is built alongside `flatc`. To review how to build the project,
please read the [Building](@ref flatbuffers_guide_building) documenation.
To run the tests, execute `flattests` from the root `flatbuffers/` directory.
For example, on [Linux](https://en.wikipedia.org/wiki/Linux), you would simply
run: `./flattests`.
## Using the FlatBuffers C++ library
*Note: See [Tutorial](@ref flatbuffers_guide_tutorial) for a more in-depth
example of how to use FlatBuffers in C++.*
FlatBuffers supports both reading and writing FlatBuffers in C++.
To use FlatBuffers in your code, first generate the C++ classes from your
schema with the `--cpp` option to `flatc`. Then you can include both FlatBuffers
and the generated code to read or write FlatBuffers.
For example, here is how you would read a FlatBuffer binary file in C++:
First, include the library and generated code. Then read the file into
a `char *` array, which you pass to `GetMonster()`.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
FlatBufferBuilder fbb;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include "flatbuffers/flatbuffers.h"
#include "monster_test_generate.h"
#include <cstdio> // For printing and file access.
Before we serialize a Monster, we need to first serialize any objects
that are contained there-in, i.e. we serialize the data tree using
depth first, pre-order traversal. This is generally easy to do on
any tree structures. For example:
FILE* file = fopen("monsterdata_test.mon", "rb");
fseek(file, 0L, SEEK_END);
int length = ftell(file);
fseek(file, 0L, SEEK_SET);
char *data = new char[length];
fread(data, sizeof(char), length, file);
fclose(file);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
auto name = fbb.CreateString("MyMonster");
unsigned char inv[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
auto inventory = fbb.CreateVector(inv, 10);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`CreateString` and `CreateVector` serialize these two built-in
datatypes, and return offsets into the serialized data indicating where
they are stored, such that `Monster` below can refer to them.
`CreateString` can also take an `std::string`, or a `const char *` with
an explicit length, and is suitable for holding UTF-8 and binary
data if needed.
`CreateVector` can also take an `std::vector`. The
offset it returns is typed, i.e. can only be used to set fields of the
correct type below. To create a vector of struct objects (which will
be stored as contiguous memory in the buffer, use `CreateVectorOfStructs`
instead.
To create a vector of nested objects (e.g. tables, strings or other vectors)
collect their offsets in a temporary array/vector, then call `CreateVector`
on that (see e.g. the array of strings example in `test.cpp`
`CreateFlatBufferTest`).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
Vec3 vec(1, 2, 3);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`Vec3` is the first example of code from our generated
header. Structs (unlike tables) translate to simple structs in C++, so
we can construct them in a familiar way.
We have now serialized the non-scalar components of of the monster
example, so we could create the monster something like this:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
auto mloc = CreateMonster(fbb, &vec, 150, 80, name, inventory, Color_Red, 0, Any_NONE);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Note that we're passing `150` for the `mana` field, which happens to be the
default value: this means the field will not actually be written to the buffer,
since we'll get that value anyway when we query it. This is a nice space
savings, since it is very common for fields to be at their default. It means
we also don't need to be scared to add fields only used in a minority of cases,
since they won't bloat up the buffer sizes if they're not actually used.
We do something similarly for the union field `test` by specifying a `0` offset
and the `NONE` enum value (part of every union) to indicate we don't actually
want to write this field. You can use `0` also as a default for other
non-scalar types, such as strings, vectors and tables. To pass an actual
table, pass a preconstructed table as `mytable.Union()` that corresponds to
union enum you're passing.
Tables (like `Monster`) give you full flexibility on what fields you write
(unlike `Vec3`, which always has all fields set because it is a `struct`).
If you want even more control over this (i.e. skip fields even when they are
not default), instead of the convenient `CreateMonster` call we can also
build the object field-by-field manually:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
MonsterBuilder mb(fbb);
mb.add_pos(&vec);
mb.add_hp(80);
mb.add_name(name);
mb.add_inventory(inventory);
auto mloc = mb.Finish();
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We start with a temporary helper class `MonsterBuilder` (which is
defined in our generated code also), then call the various `add_`
methods to set fields, and `Finish` to complete the object. This is
pretty much the same code as you find inside `CreateMonster`, except
we're leaving out a few fields. Fields may also be added in any order,
though orderings with fields of the same size adjacent
to each other most efficient in size, due to alignment. You should
not nest these Builder classes (serialize your
data in pre-order).
Regardless of whether you used `CreateMonster` or `MonsterBuilder`, you
now have an offset to the root of your data, and you can finish the
buffer using:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
FinishMonsterBuffer(fbb, mloc);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The buffer is now ready to be stored somewhere, sent over the network,
be compressed, or whatever you'd like to do with it. You can access the
start of the buffer with `fbb.GetBufferPointer()`, and it's size from
`fbb.GetSize()`.
Calling code may take ownership of the buffer with `fbb.ReleaseBufferPointer()`.
Should you do it, the `FlatBufferBuilder` will be in an invalid state,
and *must* be cleared before it can be used again.
However, it also means you are able to destroy the builder while keeping
the buffer in your application.
`samples/sample_binary.cpp` is a complete code sample similar to
the code above, that also includes the reading code below.
### Reading in C++
If you've received a buffer from somewhere (disk, network, etc.) you can
directly start traversing it using:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
auto monster = GetMonster(buffer_pointer);
auto monster = GetMonster(data);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`monster` is of type `Monster *`, and points to somewhere *inside* your
buffer (root object pointers are not the same as `buffer_pointer` !).
If you look in your generated header, you'll see it has
convenient accessors for all fields, e.g.
convenient accessors for all fields, e.g. `hp()`, `mana()`, etc:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
assert(monster->hp() == 80);
assert(monster->mana() == 150); // default
assert(strcmp(monster->name()->c_str(), "MyMonster") == 0);
printf("%d\n", monster->hp()); // `80`
printf("%d\n", monster->mana()); // default value of `150`
printf("%s\n", monster->name()->c_str()); // "MyMonster"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
These should all be true. Note that we never stored a `mana` value, so
it will return the default.
*Note: That we never stored a `mana` value, so it will return the default.*
To access sub-objects, in this case the `Vec3`:
## Reflection (& Resizing)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
auto pos = monster->pos();
assert(pos);
assert(pos->z() == 3);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There is experimental support for reflection in FlatBuffers, allowing you to
read and write data even if you don't know the exact format of a buffer, and
even allows you to change sizes of strings and vectors in-place.
If we had not set the `pos` field during serialization, it would be
`NULL`.
Similarly, we can access elements of the inventory array:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
auto inv = monster->inventory();
assert(inv);
assert(inv->Get(9) == 9);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
### Mutating FlatBuffers
As you saw above, typically once you have created a FlatBuffer, it is
read-only from that moment on. There are however cases where you have just
received a FlatBuffer, and you'd like to modify something about it before
sending it on to another recipient. With the above functionality, you'd have
to generate an entirely new FlatBuffer, while tracking what you modify in your
own data structures. This is inconvenient.
For this reason FlatBuffers can also be mutated in-place. While this is great
for making small fixes to an existing buffer, you generally want to create
buffers from scratch whenever possible, since it is much more efficient and
the API is much more general purpose.
To get non-const accessors, invoke `flatc` with `--gen-mutable`.
Similar to the reading API above, you now can:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
auto monster = GetMutableMonster(buffer_pointer); // non-const
monster->mutate_hp(10); // Set table field.
monster->mutable_pos()->mutate_z(4); // Set struct field.
monster->mutable_inventory()->Mutate(0, 1); // Set vector element.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We use the somewhat verbose term `mutate` instead of `set` to indicate that
this is a special use case, not to be confused with the default way of
constructing FlatBuffer data.
After the above mutations, you can send on the FlatBuffer to a new recipient
without any further work!
Note that any `mutate_` functions on tables return a bool, which is false
if the field we're trying to set isn't present in the buffer. Fields are not
present if they weren't set, or even if they happen to be equal to the
default value. For example, in the creation code above we set the `mana` field
to `150`, which is the default value, so it was never stored in the buffer.
Trying to call mutate_mana() on such data will return false, and the value won't
actually be modified!
One way to solve this is to call `ForceDefaults()` on a
`FlatBufferBuilder` to force all fields you set to actually be written. This
of course increases the size of the buffer somewhat, but this may be
acceptable for a mutable buffer.
Alternatively, you can use the more powerful reflection functionality:
### Reflection (& Resizing)
If the above ways of accessing a buffer are still too static for you, there is
experimental support for reflection in FlatBuffers, allowing you to read and
write data even if you don't know the exact format of a buffer, and even allows
you to change sizes of strings and vectors in-place.
The way this works is very elegant, there is actually a FlatBuffer schema that
The way this works is very elegant; there is actually a FlatBuffer schema that
describes schemas (!) which you can find in `reflection/reflection.fbs`.
The compiler `flatc` can write out any schemas it has just parsed as a binary
The compiler, `flatc`, can write out any schemas it has just parsed as a binary
FlatBuffer, corresponding to this meta-schema.
Loading in one of these binary schemas at runtime allows you traverse any
@@ -232,9 +105,10 @@ For convenient field manipulation, you can include the header
`flatbuffers/reflection.h` which includes both the generated code from the meta
schema, as well as a lot of helper functions.
And example of usage for the moment you can find in `test.cpp/ReflectionTest()`.
And example of usage, for the time being, can be found in
`test.cpp/ReflectionTest()`.
### Storing maps / dictionaries in a FlatBuffer
## Storing maps / dictionaries in a FlatBuffer
FlatBuffers doesn't support maps natively, but there is support to
emulate their behavior with vectors and binary search, which means you
@@ -260,7 +134,7 @@ To use it:
only works if the vector has been sorted, it will likely not find elements
if it hasn't been sorted.
### Direct memory access
## Direct memory access
As you can see from the above examples, all elements in a buffer are
accessed through generated accessors. This is because everything is
@@ -285,7 +159,7 @@ machines, so only use tricks like this if you can guarantee you're not
shipping on a big endian machine (an `assert(FLATBUFFERS_LITTLEENDIAN)`
would be wise).
### Access of untrusted buffers
## Access of untrusted buffers
The generated accessor functions access fields over offsets, which is
very quick. These offsets are not verified at run-time, so a malformed
@@ -342,7 +216,7 @@ accepted).
There are two ways to use text formats:
### Using the compiler as a conversion tool
#### Using the compiler as a conversion tool
This is the preferred path, as it doesn't require you to add any new
code to your program, and is maximally efficient since you can ship with
@@ -354,7 +228,7 @@ users/developers to perform, though you might be able to automate it.
This will generate the binary file `mydata_wire.bin` which can be loaded
as before.
### Making your program capable of loading text directly
#### Making your program capable of loading text directly
This gives you maximum flexibility. You could even opt to support both,
i.e. check for both files, and regenerate the binary from text when
@@ -400,7 +274,7 @@ file, that you can access as described above.
`samples/sample_text.cpp` is a code sample showing the above operations.
### Threading
## Threading
Reading a FlatBuffer does not touch any memory outside the original buffer,
and is entirely read-only (all const), so is safe to access from multiple
@@ -413,3 +287,5 @@ share instances of FlatBufferBuilder between threads (recommended), or
manually wrap it in synchronisation primites. There's no automatic way to
accomplish this, by design, as we feel multithreaded construction
of a single buffer will be rare, and synchronisation overhead would be costly.
<br>