Use of hash_map in Linux

Http://blog.sina.com.cn/s/blog_73eb956401019cq1.html

 

Hash_map in Linux

1: header file

# If 0
 # If _ gnuc __> 2
 # Include <EXT/hash_set>
 # Include <EXT/hash_map>
  Using namespace _ gnu_cxx;
 # Else
 # Include  # Include   Using namespace stdext;
 # Endif

# Endif

 

2: map with string or char * as key is not supported. If hash_map <char *, int> http_proxy_conn is used;

In comparison, the string address is actually compared, not the string itself.

Hash_map <string, int> http_proxy_conn is equivalent

Hash_map <string, Int, hash, equal> http_proxy_conn, the last two parameters are the default system

Solution:

Struct str_hash
{
 Size_t operator () (const string & Str) const
 {
   Return _ stl_hash_string (Str. c_str ());
 }
};

Struct str_equal
{
   Bool operator () (const string & S1, const string & S2) const
   {
   Return S1 = S2;
   }
};

Implement two functions: a hash function and a comparison function.

Hash_map <string, Int, str_hash, str_equal> http_proxy_conn;

You can find the correct result.

 

Hash_map <char *, Int, str_hash, str_equal> the same type should be used for http_proxy_conn.

 

1. # Include<EXT/hash_map>
     
2. # Include<Iostream> 
3. # Include<Cstring> 
4.   
5. UsingNamespaceSTD; 
6. UsingNamespace_ Gnu_cxx; 
7.   
8. StructEqstr { 
9.     Bool Operator ()(ConstChar * S1,ConstChar * S2)Const {
    
10.         ReturnStrcmp (S1, S2)=0; 
11.     } 
12. }; 
13.   
14. Int Main (){ 
15.     Hash_map <ConstChar *,Int, Hash <constChar *>, Eqstr>Months;
     
16.     Months ["January"]=31; 
17.     Months ["February"]=28; 
18.     Months ["March"]=31; 
19.     Cout<"March->" <Months ["March"]<Endl; 
20. } 
21. But not tested

Add another class

# Include # Include <string>
# Include <iostream>
Using namespace STD;
// Define the class
Class classa {
Public:
Classa (int A): c_a (){}
Int getvalue () const {return c_a ;}
Void setvalue (int A) {c_a ;}
PRIVATE:
Int c_a;
};
// 1 Define the hash function
Struct hash_a {
Size_t operator () (const class classa & A) const {
//ReturnHash <int> (classa. getvalue ());
Return A. getvalue ();
}
};
// 2 define the equal Function
Struct defaults _a {
Bool operator () (const class classa & A1, const class classa & A2) const {
ReturnA1.getvalue () = a2.getvalue ();
}
};
Int main ()
{
Hash_map <classa, String, hash_a, equal_a> hmap;
Classa A1 (12 );
Hmap [a1] = "I am 12 ";
Classa A2 (198877 );
Hmap [a2] = "I am 198877 ";
Cout Cout Return 0;
}

In the end, it was too troublesome to change it to map. string can be used as the key.