Trimmed string change it's length only by half

Question

Could anyone give some advise please. In my iOS app I am parsing XML (with a help of third-party-library) and have a problem with extra whitespaces/newLines at the beginning/end of the strings. Initial string, that return this third-party-library, it's a C++ std::wstring that I convert to NSString (the encoding should be right as the content of new NSString is equal to proper part of my XML-file). After the trim length of "empty" elements (that contain only whitespaces and new lines) doesn't become zero but change it's value by half. The code is below....

std::wstring val;
NSString *initial = [[NSString alloc] initWithBytes:val.data() length:sizeof (wchar_t)*val.size() encoding:NSUTF16LittleEndianStringEncoding];
NSString *trimmed = [initial stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

If try to output like NSLog(@"bybyby'%@'bebebe", trimmed); 'bebebe have never displayed. Looks like that there are left some new lines, whitespaces that can't be detected.

Answer 1

wchar_t is a 32-bit integer (on iOS and OS X), therefore you must use NSUTF32LittleEndianStringEncoding for the conversion to NSString.

Example:

std::wstring val (L"   Hello World   ");
NSString *initial = [[NSString alloc] initWithBytes:val.data() length:sizeof (wchar_t)*val.size() encoding:NSUTF32LittleEndianStringEncoding];
NSString *trimmed = [initial stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
NSLog(@"'%@'", trimmed);
// Output: 'Hello World'

What probably happened in your case (with NSUTF16LittleEndianStringEncoding) is that every second character in the initial string is a NUL character, which acts as a terminator when printed.