20170326STL08_STL_SGI_config.h
config.h：
1：sgi是一个公司的简称，有一个操作系统是SGI unix？，商业化的，很难接触到。
2：前端部分是版权声明，说明了可以做什么，不可做什么。
3：下面一大段注释是解释了整个文档做的事。下面代码基本就没有注释了（这是一个比较老的习惯）。
4：SGISTL里面会来检测这与编译器相关的宏是否被定义，从而得出编译器是否支持这些特性，根据这些情况来控制代码，确保跨平台不出错。
// Flags:
// * __STL_NO_BOOL: defined if the compiler doesn't have bool as a builtin
//编译器没有内部定义原生bool的时候就会定义宏 __STL_NO_BOOL
//看编译器是否有定义bool（原生bool）
// type.
// * __STL_HAS_WCHAR_T: defined if the compier has wchar_t as a builtin type.
//_WCHAR_T_IS_KEYWORD 宏，看编译器内部是否有定义wchar_t，没有的时候就会定义这个宏
//判断这些是否有定义有两种方式：1，看编译器是否有定义这些宏。2，通过编译器的版本直接判断
// * __STL_NO_DRAND48: defined if the compiler doesn't have the drand48
// function.
//求随机数的。非C标准里面的函数，Linux下面会有
//一下的就是判断是否支持某些特性
// * __STL_STATIC_TEMPLATE_MEMBER_BUG: defined if the compiler can't handle
// static members of template classes.
//是否支持在模板类里面定义一个静态成员，不支持就定义这个宏
//模板类里面如果定义静态成员，对编译器来说是个非常复杂的事情。
// * __STL_STATIC_CONST_INIT_BUG: defined if the compiler can't handle a
// constant-initializer in the declaration of a static const data member
// of integer type. (See section 9.4.2, paragraph 4, of the C++ standard.)
//static const 的这样的静态常量的定义。是否可以在类里面正常初始化
/*
class Demo
{
public:
int a_ = 0;//是个非常危险的写法，不应该这样写，不能再类中初始化
static int b_;//不可初始化
static const int c_ = 10;//仅仅是int类型可以在类里面初始化
static const double d_;//不可初始化
};
int Demo::b_ = 10;
double Demo::d_ = 2.5;
*/
// * __STL_CLASS_PARTIAL_SPECIALIZATION: defined if the compiler supports
// partial specialization of template classes.
//是否支持模板类的局部特化，基本每个编译器都会支持。
// * __STL_PARTIAL_SPECIALIZATION_SYNTAX: defined if the compiler
// supports partial specialization syntax for full specialization of
// class templates. (Even if it doesn't actually support partial
// specialization itself.)
//是否支持类模板的部分排序，偏序实例化。在有重载和特化的情况下就会有偏序。
/*//偏序实例化：和推导相关
template
void Foo(T t)
{}
template
void Foo(T *t)//重载（所有指针类型）
{}
template//这些写法在很多比较老的编译器下是不被支持的。
void Foo(const T *t)
{}
template<>
void Foo(int *t)//这个特化应该是属于(T *t)，是对他的特化，
{}*/
// * __STL_FUNCTION_TMPL_PARTIAL_ORDER: defined if the compiler supports
// partial ordering of function templates. (a.k.a partial specialization
// of function templates.)
//是否支持函数模板的部分排序，偏序实例化
// * __STL_MEMBER_TEMPLATES: defined if the compiler supports template
// member functions of classes.
//类模板里面支持模板函数,大部分编译器都支持
/*
template
class
{
public:
template
void Foo(T t){}
protected:
};*/
// * __STL_MEMBER_TEMPLATE_CLASSES: defined if the compiler supports
// nested classes that are member templates of other classes.
//是否支持一个模板类支持内嵌类为一个模板类。一般编译器都支持，甚至模板类都支持内部模板类
//内嵌类就是内部类。
/*
class Demo
{
public:
template
class Demo1
{
T data_;
public:
Demo1(T t) :data_(t)
{
}
};
Demo1 data_;
protected:
Demo(int data) :data_(data){}
};*/
// * __STL_TEMPLATE_FRIENDS: defined if the compiler supports templatized
// friend declarations.
//一个模板类是否可以为其他类的友元
//一般的都支持，否则流运算符（<<>>）就无法重载了。
// * __STL_EXPLICIT_FUNCTION_TMPL_ARGS: defined if the compiler
// supports calling a function template by providing its template
// arguments explicitly.
//是否支持函数对模板参数的推导
// * __STL_LIMITED_DEFAULT_TEMPLATES: defined if the compiler is unable
// to handle default template parameters that depend on previous template
// parameters.
//是否支持下面这种（前一个参数为后一个参数的默认值）
/*//几乎都支持
template >
class Demo
{
};*/
// * __STL_NON_TYPE_TMPL_PARAM_BUG: defined if the compiler has trouble with
// function template argument deduction for non-type template parameters.
//是否支持模板接收一个non type的一个参数，如下
/*//基本都只支持的
template
class Demo
{
public:
};*/
// * __SGI_STL_NO_ARROW_OPERATOR: defined if the compiler is unable
// to support the -> operator for iterators.
//是否支持迭代器里面重载->运算符，不支持则定义这个宏。
// * __STL_DEFAULT_CONSTRUCTOR_BUG: defined if T() does not work properly
// when T is a builtin type.
//不支持T()，定义这个宏，eg：printf("%d",int(10));，就是临时对象
//是否支持默认类型 int->int()，char->char()。
// * __STL_USE_EXCEPTIONS: defined if the compiler (in the current compilation
// mode) supports exceptions.
//是否支持异常
// * __STL_USE_NAMESPACES: defined if the compiler has the necessary
// support for namespaces.
//是否支持命名空间
// * __STL_NO_EXCEPTION_HEADER: defined if the compiler does not have a
// standard-conforming header .
//是否有exception头文件，没有就定义这个宏
// * __STL_NO_BAD_ALLOC: defined if the compiler does not have a
// header, or if does not contain a bad_alloc class. If a bad_alloc
// class exists, it is assumed to be in namespace std.
//是否有头文件，或者里面没有bad_alloc类，就定义这个宏。（必须在std命名空间里面）
// * __STL_SGI_THREADS: defined if this is being compiled for an SGI IRIX
// system in multithreaded mode, using native SGI threads instead of
// pthreads.
//线程相关
// * __STL_WIN32THREADS: defined if this is being compiled on a WIN32
// compiler in multithreaded mode.
// * __STL_PTHREADS: defined if we should use portable pthreads
// synchronization.
// * __STL_UITHREADS: defined if we should use UI / solaris / UnixWare threads
// synchronization. UIthreads are similar to pthreads, but are based
// on an earlier version of the Posix threads standard.
//以上都是线程相关的
// * __STL_LONG_LONG if the compiler has long long and unsigned long long
// types. (They're not in the C++ standard, but they are expected to be
// included in the forthcoming C9X standard.)
//是否有long long 和 unsigned long long
// * __STL_THREADS is defined if thread safety is needed.
//是否线程安全
// * __STL_VOLATILE is defined to be "volatile" if threads are being
// used, and the empty string otherwise.
//线程相关
// * __STL_USE_CONCEPT_CHECKS enables some extra compile-time error
// checking to make sure that user-defined template arguments satisfy
// all of the appropriate requirements. This may result in more
// comprehensible error messages. It incurs no runtime overhead. This
// feature requires member templates and partial specialization.
//编译器选项：开了会进行错误检查……
// * __STL_NO_USING_CLAUSE_IN_CLASS: The compiler does not handle "using"
// clauses inside of class definitions.
//类定义中不能用using。不支持的话肯定是非主流编译器
// * __STL_NO_FRIEND_TEMPLATE_CLASS: The compiler does not handle friend
// declaractions where the friend is a template class.
//不支持模板类成为其他的友元
// * __STL_NO_FUNCTION_PTR_IN_CLASS_TEMPLATE: The compiler does not
// support the use of a function pointer type as the argument
// for a template.
//不支持函数指针成为一个类模板参数
//template,T不能为函数指针
// * __STL_MEMBER_TEMPLATE_KEYWORD: standard C++ requires the template
// keyword in a few new places (14.2.4). This flag is set for
// compilers that support (and require) this usage.
// User-settable macros that control compilation:
//用户自定义的
// * __STL_USE_SGI_ALLOCATORS: if defined, then the STL will use older
// SGI-style allocators, instead of standard-conforming allocators,
// even if the compiler supports all of the language features needed
// for standard-conforming allocators.
//被定义的话，会用老版本的sgi的alloc。
// * __STL_NO_NAMESPACES: if defined, don't put the library in namespace
// std, even if the compiler supports namespaces.
//将生成的library不加到namespace std中。
// * __STL_NO_RELOPS_NAMESPACE: if defined, don't put the relational
// operator templates (>, <=. >=, !=) in namespace std::rel_ops, even
// if the compiler supports namespaces and partial ordering of
// function templates.
// * __STL_ASSERTIONS: if defined, then enable runtime checking through the
// __stl_assert macro.
// * _PTHREADS: if defined, use Posix threads for multithreading support.
// * _UITHREADS:if defined, use SCO/Solaris/UI threads for multithreading
// support
// * _NOTHREADS: if defined, don't use any multithreading support.
// * _STL_NO_CONCEPT_CHECKS: if defined, disables the error checking that
// we get from __STL_USE_CONCEPT_CHECKS.
// * __STL_USE_NEW_IOSTREAMS: if defined, then the STL will use new,
// standard-conforming iostreams (e.g. the header). If not
// defined, the STL will use old cfront-style iostreams (e.g. the
// header).
// Other macros defined by this file:
// * bool, true, and false, if __STL_NO_BOOL is defined.
// * typename, as a null macro if it's not already a keyword.
// * explicit, as a null macro if it's not already a keyword.
// * namespace-related macros (__STD, __STL_BEGIN_NAMESPACE, etc.)
// * exception-related macros (__STL_TRY, __STL_UNWIND, etc.)
// * __stl_assert, either as a test or as a null macro, depending on
// whether or not __STL_ASSERTIONS is defined.