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Make the Parser independent from the global C-locale (#5028)

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* Make the Parser independent from the global C-locale

* Set a specific test locale using the environment variable FLATBUFFERS_TEST_LOCALE

* Remove redundant static qualifiers
This commit is contained in:
Vladimir Glavnyy
2018-11-17 00:24:06 +07:00
committed by Wouter van Oortmerssen
parent d6b1ce09cf
commit 5f32f94810
15 changed files with 480 additions and 277 deletions
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docs/source/CppUsage.md
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@@ -499,11 +499,47 @@ To use scalars, simply wrap them in a struct.
## Depth limit of nested objects and stack-overflow control
The parser of Flatbuffers schema or json-files is kind of recursive parser.
To avoid stack-overflow problem the parser has a built-in limiter of recursion depth.
Number of nested declarations in a schema or number of nested json-objects is limited.
By default, this depth limit set to `64`.
It is possible to override this limit with `FLATBUFFERS_MAX_PARSING_DEPTH` definition.
This definition can be helpful for testing purposes or embedded applications.
For details see [build](@ref flatbuffers_guide_building) of CMake-based projects.
To avoid stack-overflow problem the parser has a built-in limiter of
recursion depth. Number of nested declarations in a schema or number of
nested json-objects is limited. By default, this depth limit set to `64`.
It is possible to override this limit with `FLATBUFFERS_MAX_PARSING_DEPTH`
definition. This definition can be helpful for testing purposes or embedded
applications. For details see [build](@ref flatbuffers_guide_building) of
CMake-based projects.
## Dependence from C-locale {#flatbuffers_locale_cpp}
The Flatbuffers [grammar](@ref flatbuffers grammar) uses ASCII
character set for identifiers, alphanumeric literals, reserved words.
Internal implementation of the Flatbuffers depends from functions which
depend from C-locale: `strtod()` or `strtof()`, for example.
The library expects the dot `.` symbol as the separator of an integer
part from the fractional part of a float number.
Another separator symbols (`,` for example) will break the compatibility
and may lead to an error while parsing a Flatbuffers schema or a json file.
The Standard C locale is a global resource, there is only one locale for
the entire application. Some modern compilers and platforms have
locale-independent or locale-narrow functions `strtof_l`, `strtod_l`,
`strtoll_l`, `strtoull_l` to resolve this dependency.
These functions use specified locale rather than the global or per-thread
locale instead. They are part of POSIX-2008 but not part of the C/C++
standard library, therefore, may be missing on some platforms.
The Flatbuffers library try to detect these functions at configuration and
compile time:
- `_MSC_VER >= 1900`: check MSVC2012 or higher for MSVC buid
- `_XOPEN_SOURCE>=700`: check POSIX-2008 for GCC/Clang build
- `check_cxx_symbol_exists(strtof_l stdlib.h)`: CMake check of `strtod_f`
After detection, the definition `FLATBUFFERS_LOCALE_INDEPENDENT` will be
set to `0` or `1`.
It is possible to test the compatibility of the Flatbuffers library with
a specific locale using the environment variable `FLATBUFFERS_TEST_LOCALE`:
```sh
>FLATBUFFERS_TEST_LOCALE="" ./flattests
>FLATBUFFERS_TEST_LOCALE="ru_RU.CP1251" ./flattests
```
<br>