Swift Printf

func swiftprintf(format: String, _ arguments: CVarArg...) -> String? {
    return withVaList(arguments) { va_list in
        var buffer: UnsafeMutablePointer<Int8>? = nil
        return format.withCString { CString in
            guard vasprintf(&buffer, CString, va_list) != 0 else {
                return nil
            }
            return String(validatingUTF8: buffer!)
        }
    }
}

swiftprintf(format: "√2 ≅ %g", sqrt(2.0))

输出结果：√2 ≅ 1.41421