【2014-06-18】C++ STL读书笔记：stl_construct.h

[历史归档]本文原发布于 cstriker1407.info 个人博客内容为历史存档仅供参考。发布时间2014-06-18 标题C STL读书笔记stl_construct.h分类编程 / C C / C STL 标签CC·stl·constructC STL读书笔记stl_construct.h备注stl\_construct.hnew备注本读书笔记基于侯捷先生的《STL源码剖析》截图和注释版权均属于原作者所有。本读书笔记中的源码部分直接拷贝自SGI-STL部分代码删除了头部的版权注释但代码版权属于原作者。小弟初看stl很多代码都不是太懂注释可能有很多错误还请路过的各位大牛多多给予指导。stl_construct.h主要用于封装各种构造与析构函数部分源码如下为了节省版面删除了头部的版权注释#ifndef_STL_CONSTRUCT_H#define_STL_CONSTRUCT_H1//这里包含了new后面便可以使用placement newnew文件源码后面附上。#includenew#includebits/move.h//在std命名空间中_GLIBCXX_BEGIN_NAMESPACE(std)/** * Constructs an object in existing memory by invoking an allocated * objects constructor with an initializer. *///新实例的内存已经申请好了这里调用构造函数将其构造好。templatetypename_T1,typename_T2inlinevoid#ifdef__GXX_EXPERIMENTAL_CXX0X__// Allow perfect forwarding_Construct(_T1*__p,_T2__value)#else_Construct(_T1*__p,const_T2__value)#endif{// _GLIBCXX_RESOLVE_LIB_DEFECTS// 402. wrong new expression in allocator::construct::new(static_castvoid*(__p))_T1(_GLIBCXX_FORWARD(_T2,__value));//placement new可简单的理解为 _T1(__value);}/** * Destroy the object pointed to by a pointer type. *///析构单个实例//只有一个入参直接调用实例的析构函数。templatetypename_Tpinlinevoid_Destroy(_Tp*__pointer){__pointer-~_Tp();}//有两个参数分别是头尾部[)的iterator,通过iterator的累加分别调用一个入参的_Destroy函数进行析构//此版本的_Destroy_aux是需要【显式的】调用析构函数的。templateboolstruct_Destroy_aux{templatetypename_ForwardIteratorstaticvoid//这里使用的是static void这样便可以直接通过类名来调用了_Destroy_aux::,非常方便__destroy(_ForwardIterator __first,_ForwardIterator __last){for(;__first!__last;__first)std::_Destroy(*__first);}};//同上//此版本的_Destroy_aux是【不需要】调用析构函数的。个人的理解是如果实例比较简单不需要显示的调用析构函数//那么可以进行流程的优化省略掉调用析构函数的流程提高运行效率。templatestruct_Destroy_auxtrue{templatetypename_ForwardIteratorstaticvoid__destroy(_ForwardIterator,_ForwardIterator){}};/** * Destroy a range of objects. If the value_type of the object has * a trivial destructor, the compiler should optimize all of this * away, otherwise the objects destructors must be invoked. *///析构多个实例2参数版本//这里首先对是否需要调用析构函数进行判断如果实例比较简单比如没有动态内存的申请析构时无需显示调用析构函数比如类定义时析构函数就未实现。//就可以进行代码优化调用_Destroy_aux的不同版本。templatetypename_ForwardIteratorinlinevoid_Destroy(_ForwardIterator __first,_ForwardIterator __last){typedeftypenameiterator_traits_ForwardIterator::value_type _Value_type;std::_Destroy_aux__has_trivial_destructor(_Value_type)::__destroy(__first,__last);}/** * Destroy a range of objects using the supplied allocator. For * nondefault allocators we do not optimize away invocation of * destroy() even if _Tp has a trivial destructor. *///如果实例不是通过默认的allocator,而是通过其他的自定义的allocator来申请的那么在析构时就不能调用默认的析构函数了//就必须使用自定义的allocator的析构函数上面的注释也提到了这一点。templatetypename_Tpclassallocator;templatetypename_ForwardIterator,typename_Allocatorvoid_Destroy(_ForwardIterator __first,_ForwardIterator __last,_Allocator__alloc){for(;__first!__last;__first)__alloc.destroy(*__first);}//如果调用模板函数时显式的提到了allocator但不是自定义版本的那么底层的实现依然是默认的allocator。//直接调用2参数版本。templatetypename_ForwardIterator,typename_Tpinlinevoid_Destroy(_ForwardIterator __first,_ForwardIterator __last,allocator_Tp){_Destroy(__first,__last);}_GLIBCXX_END_NAMESPACE#endif/* _STL_CONSTRUCT_H */new文件部分源码如下为了节省版面删除了头部的版权注释#ifndef_NEW#define_NEW#pragmaGCC system_header#includecstddef#includeexception#pragmaGCC visibilitypush(default)externC{namespacestd{/** * brief Exception possibly thrown by c new. * ingroup exceptions * * c bad_alloc (or classes derived from it) is used to report allocation * errors from the throwing forms of c new. *///声明了一个【 bad_alloc 】异常类用来在new/delete失败时抛出class_GLIBCXX_IMPORTbad_alloc:publicexception{public:bad_alloc()throw(){}// This declaration is not useless:// http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118virtual~bad_alloc()throw();// See comment in eh_exception.cc.virtualconstchar*what()constthrow();};structnothrow_t{};externconstnothrow_t nothrow;/** If you write your own error handler to be called by c new, it must * be of this type. */typedefvoid(*new_handler)();/// Takes a replacement handler as the argument, returns the/// previous handler.new_handlerset_new_handler(new_handler)throw();}// namespace std//{/** These are replaceable signatures: * - normal single new and delete (no arguments, throw c bad_alloc on error) * - normal array new and delete (same) * - c nothrow single new and delete (take a c nothrow argument, return * c NULL on error) * - c nothrow array new and delete (same) * * Placement new and delete signatures (take a memory address argument, * does nothing) may not be replaced by a users program. *///各种重载 new/delete 运算符声明void*operatornew(std::size_t)throw(std::bad_alloc);void*operatornew[](std::size_t)throw(std::bad_alloc);voidoperatordelete(void*)throw();voidoperatordelete[](void*)throw();void*operatornew(std::size_t,conststd::nothrow_t)throw();void*operatornew[](std::size_t,conststd::nothrow_t)throw();voidoperatordelete(void*,conststd::nothrow_t)throw();voidoperatordelete[](void*,conststd::nothrow_t)throw();//Placement new 和 Placement delete 函数实现的非常简单// Default placement versions of operator new.inlinevoid*operatornew(std::size_t,void*__p)throw(){return__p;}inlinevoid*operatornew[](std::size_t,void*__p)throw(){return__p;}// Default placement versions of operator delete.inlinevoidoperatordelete(void*,void*)throw(){}inlinevoidoperatordelete[](void*,void*)throw(){}//}}// extern C#pragmaGCC visibility pop#endif