Re: std::string and case insensitive comparison
"Mosfet" <anonymous@free.fr> wrote in message
news:469fede8$0$18501$426a74cc@news.free.fr...
Jim Langston a ?crit :
"Mosfet" <anonymous@free.fr> wrote in message
news:469fe09f$0$24914$426a74cc@news.free.fr...
Hi,
what is the most efficient way of doing a case insensitive comparison ?
I am trying to write a universal String class and I am stuck with the
case insensitive part :
TCHAR is a char in MultiByte String env (MBCS)
and wchar_t if UNICODE
#if defined(WIN32) || defined(UNDER_CE)
typedef std::basic_string<TCHAR, std::char_traits<TCHAR>,
std::allocator<TCHAR> > tstring;
#else
#endif
#endif
class String : public Object
{
private:
tstring m_str;
public:
String(){}
String(LPCTSTR lpsz)
{
m_str = lpsz;
}
String(tstring str)
{
m_str = str;
}
// Comparison
int Compare( LPCTSTR psz ) const
{
return m_str.compare(psz);
}
int CompareNoCase( LPCTSTR psz ) const
{
???
}
// Convert the string to lowercase
String& MakeLower( LPCTSTR psz )
{
std::transform(m_str.begin(), m_str.end(), m_str.begin(), tolower);
return *this;
}
}
This is what I use. I'm not sure if it's optimal, but it works.
bool StrLowCompare( std::string String1, std::string String2 )
{
std::transform(String1.begin(), String1.end(), String1.begin(),
tolower);
std::transform(String2.begin(), String2.end(), String2.begin(),
tolower);
return String1 == String2;
}
Ir doesn't seem very efficient...
No, it doesn't. But then, there is no way to do a case insensitive compare
without converting both to either upper or lower. Or to determine if one is
uppercase before converting to lower, but it probably takes about the same
amount of time for the if statement.
Basically, that's the way case insensitve works. You convert both to upper
or lower, then compare, or compare character by character converting.
It may be faster to compare character by character and see if you can return
early without having to go through the whole string, but the you're doing a
bunch of if statments anyway. I.E something like: (untested code)
bool StrLowCompare( std::string& String1, std::string& String2 )
{
if ( String1.size() != String2.size() )
return false;
for ( std::string::size_type i = 0; i < String1.size(); ++i )
{
if ( tolower( String1[i] ) != tolower( String2[i] )
return false;
}
return true;
}