feedc0de/boost_conversion
1
0
Fork 0
forked from boostorg/conversion
Code Pull Requests Activity

Update documentation ( more info about stream character type detection + warn about new unicode types support; refs #6786, refs #6663)

Browse Source 
[SVN r78044]
This commit is contained in:
Antony Polukhin
2012-04-17 16:27:50 +00:00
parent 746d466e38
commit 9ff79f4df9
1 changed files with 18 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
doc/lexical_cast.qbk
View File

@@ -97,7 +97,21 @@ The requirements on the argument and result types are:
* Target is CopyConstructible [20.1.3].
* Target is DefaultConstructible, meaning that it is possible to default-initialize an object of that type [8.5, 20.1.4].
The character type of the underlying stream is assumed to be char unless either the Source or the Target requires wide-character streaming, in which case the underlying stream uses `wchar_t`. Source types that require wide-character streaming are `wchar_t`, `wchar_t *`, and `std::wstring`. Target types that require wide-character streaming are `wchar_t` and `std::wstring`.
The character type of the underlying stream is assumed to be `char` unless either the `Source` or the `Target` requires wide-character streaming, in which case the underlying stream uses `wchar_t`, `char16_t` or `char32_t`. Wide-character streaming is currently detected for:
* Single character: `wchar_t`, `char16_t`, `char32_t`
* Arrays of characters: `wchar_t *`, `char16_t *`, `char32_t *`, `const wchar_t *`, `const char16_t *`, `const char32_t *`
* Strings: `std::basic_string`, `boost::containers::basic_string`
* Character ranges: `boost::iterator_range`, `boost::iterator_range`
[important Many compilers and runtime libraries fail to make conversions using new Unicode characters. Make shure that the following code compiles and outputs nonzero values, before using new types:
``
std::cout
<< booat::lexical_cast<std::u32string>(1.0).size()
<< " "
<< booat::lexical_cast<std::u16string>(1.0).size();
``
]
Where a higher degree of control is required over conversions, `std::stringstream` and `std::wstringstream` offer a more appropriate path. Where non-stream-based conversions are required, `lexical_cast` is the wrong tool for the job and is not special-cased for such scenarios.
[endsect]
@@ -146,9 +160,9 @@ Consider the following example:
This is a good generic solution for most use cases.
But we can make it even faster for some performance critical applications. During conversion, we loose speed at:
* `std::ostream` construction (it makes some heap allocations)
* `operator <<` (it copyies one by one all the symbols to an instance of `std::ostream`)
* `std::ostream` destruction (it makes some heap deallocations)
* `std::ostream` construction (it makes some heap allocations)
* `operator <<` (it copyies one by one all the symbols to an instance of `std::ostream`)
* `std::ostream` destruction (it makes some heap deallocations)
We can avoid all of this, by specifieng an overload for `boost::lexical_cast`:
``