iOS 获取字符串的字节长度

- (int)convertToByte:(NSString*)str {
    int strlength = 0;
    char* p = (char*)[str cStringUsingEncoding:NSUnicodeStringEncoding];
    for (int i=0 ; i<[str lengthOfBytesUsingEncoding:NSUnicodeStringEncoding] ;i++) {
        if (*p) {
            p++;
            strlength++;
        }
        else {
            p++;
        }
    }
    return (strlength+1)/2;
}