iOS字符串移位

话不多说,直接上代码:
写在NSString的category里的方法:

- (NSString *)displacementWithLength:(int)length {
    NSString *string = @"";
    unsigned char css[self.length];
    memcpy(css, [self cStringUsingEncoding:NSUTF8StringEncoding], self.length);
    for (int i = 0; i < sizeof(css); i++) {
        NSLog(@"%c",css[i]+length);
        string = [string stringByAppendingFormat:@"%c",css[i]+length];
    }
    return string;
}

length代表移动的位数