问题描述
我正在尝试编写带有参数的流操纵器.我的班级是3 int的CDate(年，月，日).因此，我需要制作操纵器date_format(const char*).例如:
I'm trying to write a stream manipulator with arguments.I have class with 3 int's CDate(Year, Month, Day).So I need to make manipulator date_format(const char*).e.g. :
CDate a(2006, 5, 15);
cout <<"DATE IS : " << date_format("%Y-hello-%d-world-%m-something-%d%d") << a;
输出将是:
DATE IS : 2006-hello-15-world-5-something-1515
猜猜我需要使用
ios_base & dummy_date_format_manipulator ( ios_base & x )
{
return x;
}
ios_base & ( * ( date_format ( const char * fmt ) ) )( ios_base & x )
{
return dummy_date_format_manipulator;
}
但是我不知道怎么做.
推荐答案
您可以为此使用pword数组.C ++中的每个iostream都有两个与之关联的数组.
You can use pword array for this.Every iostream in C++ has two arrays associated with it.
ios_base::iword - array of ints
ios_base::pword - array of void* pointers
您可以在其中存储自己的数据.若要获取索引，该索引引用所有iword和pword数组中的空元素，则应使用函数std::ios_base::xalloc().它返回int，您可以将其用作*word中的唯一索引.您应该在启动时获取一次该索引，然后将其用于*word的所有操作.
You can store you own data in it. To obtain an index, that refers to an empty element in all iword and pword arrays you should use function std::ios_base::xalloc(). It returns int that you can use as an unique index in *word.You should obtain that index once on the start-up, and than use it for all operations with *word.
然后编程您自己的操作将如下所示:
Then programming your own manip will look like:
操纵器函数接收对ios_base对象的引用和对格式字符串的指针，只需将该指针存储在pword
Manipulator function, that receives reference to ios_base object and pointer to the format string, simply stores that pointer in pword
iosObject.pword(index_from_xalloc) = formatString
然后，重载的运算符<<(>>)以相同的方式从iostream对象获取格式字符串.之后，您只需参考格式进行转换即可.
Then overloaded operator << (>>) obtains format string from the iostream object in the same way. After that you just make a conversion referencing to the format.
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