std::ios_base::pword

科技促进发展：监督办[医]基：：pword

void*& pword( int index

首先，分配或调整私有存储%28动态数组的大小。void*或另一个可索引的数据结构%29足以使index一个有效的索引，然后返回对void*元素的私有存储的索引。index...

对此的任何操作都可能使引用无效。ios_base对象，包括对pword()，但是保留存储的值，以便从pword(index)使用相同的索引，以后将产生相同的值%28，直到下一次调用copyfmt()29%。该值可用于任何目的。元素的索引必须由xalloc()的其他用户之间的冲突。ios_base可能会发生。新元素初始化为NULL...

如果分配失败，调用std::basic_ios<>::setstate(badbit)可能会std::ios_base::failure...

参数

index	-	index value of the element

返回值

对元素的引用。

例外

可抛std::ios_base::failure当设置坏位时。

注记

中存储的指针pword需要管理，register_callback()可用于安装处理程序，根据需要执行深度复制或取消分配。

例

将基类pword存储用于派生流对象的运行时类型标识。

二次

#include <iostream>
 
template<class charT, class traits = std::char_traits<charT> >
class mystream : public std::basic_ostream<charT, traits>
{
 public:
    static const int xindex;
    mystream(std::basic_ostream<charT, traits>& ostr) :
        std::basic_ostream<charT, traits>(ostr.rdbuf())
    {
         this->pword(xindex) = this;
    }
 
    void myfn()
    {
        *this << "[special handling for mystream]";
    }
};
 
// each specialization of mystream obtains a unique index from xalloc()
template<class charT, class traits>
const int mystream<charT, traits>::xindex = std::ios_base::xalloc(
 
// This I/O manipulator will be able to recognize ostreams that are mystreams
// by looking up the pointer stored in pword
template<class charT, class traits>
std::basic_ostream<charT,traits>& mymanip(std::basic_ostream<charT,traits>& os)
{
 if (os.pword(mystream<charT,traits>::xindex) == &os) 
    static_cast<mystream<charT,traits>&>(os).myfn(
 return os;
}
 
int main()
{
    std::cout << "cout, narrow-character test " << mymanip << '\n';
 
    mystream<char> myout(std::cout
    myout << "myout, narrow-character test " << mymanip << '\n';
 
    std::wcout << "wcout, wide-character test " << mymanip << '\n';
 
    mystream<wchar_t> mywout(std::wcout
    mywout << "mywout, wide-character test " << mymanip << '\n';
}

二次

产出：

二次

cout, narrow-character test 
myout, narrow-character test [special handling for mystream]
wcout, wide-character test 
mywout, wide-character test [special handling for mystream]

二次

另见

iword	resizes the private storage if necessary and access to the long element at the given index (public member function)
xalloc static	returns a program-wide unique integer that is safe to use as index to pword() and iword() (public static member function)

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