From 554fd8c5195424bdbcabf5de30fdc183aba391bd Mon Sep 17 00:00:00 2001 From: upstream source tree Date: Sun, 15 Mar 2015 20:14:05 -0400 Subject: obtained gcc-4.6.4.tar.bz2 from upstream website; verified gcc-4.6.4.tar.bz2.sig; imported gcc-4.6.4 source tree from verified upstream tarball. downloading a git-generated archive based on the 'upstream' tag should provide you with a source tree that is binary identical to the one extracted from the above tarball. if you have obtained the source via the command 'git clone', however, do note that line-endings of files in your working directory might differ from line-endings of the respective files in the upstream repository. --- libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html | 55 +++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html (limited to 'libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html') diff --git a/libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html b/libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html new file mode 100644 index 000000000..8fa7981de --- /dev/null +++ b/libstdc++-v3/doc/html/manual/bk01pt03ch17s02.html @@ -0,0 +1,55 @@ + + +Semantics
Semantics
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Semantics

+

A program that uses the C++ standard library correctly + will maintain the same semantics under debug mode as it had with + the normal (release) library. All functional and exception-handling + guarantees made by the normal library also hold for the debug mode + library, with one exception: performance guarantees made by the + normal library may not hold in the debug mode library. For + instance, erasing an element in a std::list is a + constant-time operation in normal library, but in debug mode it is + linear in the number of iterators that reference that particular + list. So while your (correct) program won't change its results, it + is likely to execute more slowly.

libstdc++ includes many extensions to the C++ standard library. In + some cases the extensions are obvious, such as the hashed + associative containers, whereas other extensions give predictable + results to behavior that would otherwise be undefined, such as + throwing an exception when a std::basic_string is + constructed from a NULL character pointer. This latter category also + includes implementation-defined and unspecified semantics, such as + the growth rate of a vector. Use of these extensions is not + considered incorrect, so code that relies on them will not be + rejected by debug mode. However, use of these extensions may affect + the portability of code to other implementations of the C++ standard + library, and is therefore somewhat hazardous. For this reason, the + libstdc++ debug mode offers a "pedantic" mode (similar to + GCC's -pedantic compiler flag) that attempts to emulate + the semantics guaranteed by the C++ standard. For + instance, constructing a std::basic_string with a NULL + character pointer would result in an exception under normal mode or + non-pedantic debug mode (this is a libstdc++ extension), whereas + under pedantic debug mode libstdc++ would signal an error. To enable + the pedantic debug mode, compile your program with + both -D_GLIBCXX_DEBUG + and -D_GLIBCXX_DEBUG_PEDANTIC . + (N.B. In GCC 3.4.x and 4.0.0, due to a bug, + -D_GLIBXX_DEBUG_PEDANTIC was also needed. The problem has + been fixed in GCC 4.0.1 and later versions.)

The following library components provide extra debugging + capabilities in debug mode:

N.B. although there are precondition checks for some string operations, +e.g. operator[], +they will not always be run when using the char and +wchar_t specialisations (std::string and +std::wstring). This is because libstdc++ uses GCC's +extern template extension to provide explicit instantiations +of std::string and std::wstring, and those +explicit instantiations don't include the debug-mode checks. If the +containing functions are inlined then the checks will run, so compiling +with -O1 might be enough to enable them. Alternatively +-D_GLIBCXX_EXTERN_TEMPLATE=0 will suppress the declarations +of the explicit instantiations and cause the functions to be instantiated +with the debug-mode checks included, but this is unsupported and not +guaranteed to work. For full debug-mode support you can use the +__gnu_debug::basic_string debugging container directly, +which always works correctly. +

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