substring from main string using CString library functions

Copy a substring from main string using CString library functions.

CString  FilterCriteria ="MESSAGE=2 AND READ = 2 AND Instance=\'SMS/MMS\' 
AND Folder=\'inbox\'";
CString  o_filter;

Now, i want to copy Instance=\'SMS/MMS\' AND Folder=\'inbox\' from FilterCriteria to o_filteredFilterCriteria.

Expected result:

o_filter = Instance=\'SMS/MMS\' AND Folder=\'inbox\'.

Program:

int Pos = FilterCriteria.find(instance); 
int First_Pos = FilterCriteria.find("'");
string temp_str = FilterCriteria.substr(First_Pos+1);
string temp_str =FilterCriteria.
int Second_Pos = temp_str.find("'");  

string tempInstance = FilterCriteria.substr(Pos, First_Pos+Second_Pos-
Pos+2);

temp_str = "";

Pos = FilterCriteria.find(folder);// folder position
string Fold_Str = FilterCriteria.substr(Pos);//string after the folder 
First_Pos = Fold_Str.find("'");// first occurence of string
temp_str = Fold_Str.substr(First_Pos+1);// string after '
Second_Pos = temp_str.find("'");// first occurence of ' in string after '
string tempFolder=originalFilterCriteria.substr(Pos, First_Pos+Second_Pos-
Pos+2);

if ( !tempInstance.isEmpty())
{
    o_filter = " AND ";
    o_filter += tempInstance;
}

if (!tempFolder.isEmpty())
{
    o_filter = " AND ";
    o_filter += tempFolder;
}

This code works for string.h library. The same code doesn't work for CString 
functions as CString library doesn't have substr() function.