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Document requirement for custom string types to implement empty() and be constructible from std::string.

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Add new option --cpp-str-flex-ctor to construct custom string types not via std::string, but (char * + length).
This commit is contained in:
Luca Longinotti
2019-03-01 16:15:36 +01:00
parent 28cb2e92d5
commit 92b90d7f0f
5 changed files with 44 additions and 9 deletions
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docs/source/CppUsage.md
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@@ -255,14 +255,24 @@ you, so you'll have to manage their lifecycles manually. To reference the
pointer type specified by the `--cpp-ptr-type` argument to `flatc` from a
flatbuffer field set the `cpp_ptr_type` attribute to `default_ptr_type`.
# Using different string type.
By default the object tree is built out of `std::string`, but you can
influence this either globally (using the `--cpp-str-type` argument to
`flatc`) or per field using the `cpp_str_type` attribute.
The type must support T::c_str() and T::length() as member functions.
The type must support T::c_str(), T::length() and T::empty() as member functions.
Further, the type must be constructible from std::string, as by default a
std::string instance is constructed and then used to initialize the custom
string type. This behavior impedes efficient and zero-copy construction of
custom string types; the `--cpp-str-flex-ctor` argument to `flatc` or the
per field attribute `cpp_str_flex_ctor` can be used to change this behavior,
so that the custom string type is constructed by passing the pointer and
length of the FlatBuffers String. The custom string class will require a
constructor in the following format: custom_str_class(const char *, uint32_t).
Please note that the character array is not guaranteed to be NUL terminated,
you should always use the provided size to determine end of string.
## Reflection (& Resizing)