NSString中怎么去掉两端的空格

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        NSString * str = @" sdjlsk  lkdjsld ";
        
       str = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
        NSLog(@"\n%@",str);
    }
    return 0;
}

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2015-10-01 20:36:42.602 2222[2395:133083]
sdjlsk  lkdjsld
Program ended with exit code: 0