using Boost.foreach foreachAuthor: Jiang
Blog:http://blog.csdn.net/jiangfriend
Time: 2007-7-28 14:56
Friends with other languages must have been greatly facilitated by this command, but C + + did not provide, as 1.34.0 Boost.foreach officially became part of boost, and Boost.foreach quite easy to use. From then on C + + also have foreach.
first, the use of methodsGrammar:
Boost_foreach (VAR, COL)
{
Todo
}
Very simple and clear.
Cases:
#include <string>
#include <iostream>
using namespace Std;
#include <boost/foreach.hpp>
int main (int argc, char* argv[])
{
String Str ("The quick brown fox jumps over the lazy dog");
Boost_foreach (char c,str)
{
cout<<c<<endl;
}
return 0;
}
If #define foreach Boost_foreach, you can almost think of foreach as an internal reserved keyword.
ii. expansion of foreachNot all objects can support foreach.
Such as:
struct MyString
{
String str;
};
Then we need to manually extend the foreach itself.
Accordingly, you need to rewrite the following related functions and structures
range_iterator<link>;
Boost_range_begin (link&);
Boost_range_end (link&);
range_const_iterator<link>; Constant
Boost_range_begin (const link&);
Boost_range_end (const link&);
The Modify program is
#define foreach Boost_foreach
#include <string>
#include <iostream>
using namespace Std;
#include <boost/foreach.hpp>
struct MyString
{
String str;
typedef string::iterator iterator;
typedef string::const_iterator Const_iterator;
MyString (const string& str): str (str)
{
}
Inline iterator begin (void)
{
return Str.begin ();
}
Inline iterator end (void)
{
return Str.end ();
}
inline const_iterator begin (void) const
{
return Str.begin ();
}
Inline const_iterator End (void) const
{
return Str.end ();
}
};
/**
* The following is the main rewrite code
*/
Namespace boost
{
Template<>
struct range_iterator<mystring>
{
typedef mystring::iterator type;
};
Template<>
struct range_const_iterator<mystring>
{
typedef mystring::const_iterator type;
};
Inline Range_iterator<mystring>::type boost_range_begin (mystring& str)
{
return Str.begin ();
}
Inline Range_iterator<mystring>::type boost_range_end (mystring& str)
{
return Str.end ();
}
Inline Range_const_iterator<mystring>::type boost_range_const_begin (const mystring& STR)
{
return Str.begin ();
}
Inline Range_const_iterator<mystring>::type boost_range_const_end (const mystring& STR)
{
return Str.end ();
}
}
int main (int argc, char* argv[])
{
MyString Str ("The quick brown fox jumps over the lazy dog");
foreach (char c,str)
{
cout<<c<<endl;
}
return 0;
}
It's a bit annoying, but it's quite simple.
iii. Matters of noteBoost_foreach (std::p air<int,int>& p,m) is not supported due to language limitations
Because there is a comma between int and int, and Boost_foreach is a macro, Boost_foreach is understood as (Std:pair<int, int>&p,m)
Such as
int main (int argc, char* argv[])
{
Map<int,int> m;
M[1]=1;
foreach (const map<int,int>::value_type& p,m)//Error
{
cout<<p.first<<endl;
}
return 0;
}
Need to be rewritten as
int main (int argc, char* argv[])
{
typedef map<int,int> Map_int;
Map_int m;
M[1]=1;
foreach (const map_int::value_type& p,m)
{
cout<<p.first<<endl;
}
return 0;
}
Four: Post-languageforeach simplifies the programming process is really gratifying, but the boost penetration rate is not high, but also only internal use, more regrettable.
In addition, Boost.foreach for non-copyable and lightweight also have a special treatment, the specific situation can refer to the official documents.
Five: RELATED LINKSforeach Official document Http://www.boost.org/doc/html/foreach.html
Boost Official site http://www.boost.org
