C语言用变量来存储数据，用函数来定义一段可以重复使用的代码，它们最终都要放到内存中才能供 CPU 使用。
数据和代码都以二进制的形式存储在内存中，计算机无法从格式上区分某块内存到底存储的是数据还是代码。当程序被加载到内存后，操作系统会给不同的内存块指定不同的权限，拥有读取和执行权限的内存块就是代码，而拥有读取和写入权限（也可能只有读取权限）的内存块就是数据。
CPU 只能通过地址来取得内存中的代码和数据，程序在执行过程中会告知 CPU 要执行的代码以及要读写的数据的地址。如果程序不小心出错，或者开发者有意为之，在 CPU 要写入数据时给它一个代码区域的地址，就会发生内存访问错误。这种内存访问错误会被硬件和操作系统拦截，强制程序崩溃，程序员没有挽救的机会。编译和链接过程的一项重要任务就是找到变量和函数名所对应的地址
如下例子：a为正常变量，p为指针变量，p指向了100的地址
int a = 100;
int *p = &a;
本文70%为组合翻译，详见最后引用，30%为原创内容
定版为version1.0,目前为 Version 0.1 表示正在撰写或者翻译
network layer: logical communication between hosts
网络层：主机之间的逻辑通信
transport layer: logical communication between processes–relies on, enhances, network layer services
传输层:是主机之间的进程通信，是用来加强网络层的
The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermediainformation systems. HTTP has been in use by the World-Wide Web global information initiative since 1990. The first version of HTTP, referred to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet. HTTP/1.0, as defined by RFC 1945 [6], improved the protocol by allowing messages to be in the format of MIMElike messages, containing metainformation about the data transferred and modifiers on the request/response semantics. However, HTTP/1.0 does not sufficiently take into consideration the effects of hierarchical proxies,caching, the need for persistent connections, or virtual hosts. In addition, the proliferation of incompletelyimplemented applications calling themselves “HTTP/1.0” has necessitated a protocol version change in order for two communicating applications to determine each other’s true capabilities.
This specification defines the protocol referred to as “HTTP/1.1”. This protocol includes more stringent
requirements than HTTP/1.0 in order to ensure reliable implementation of its features.
Practical information systems require more functionality than simple retrieval, including search, front-end update,and annotation. HTTP allows an open-ended set of methods and headers that indicate the purpose of a request [47].It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) [3], as a location (URL)[4] or name (URN) [20], for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by Internet mail [9] as defined by the Multipurpose Internet Mail Extensions (MIME) [7].
HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems, including those supported by the SMTP [16], NNTP [13], FTP [18], Gopher [2], and WAIS [10]protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications.
HTTP1.1重点增加了可靠性传输的功能
“ Clickjacking （点击劫持）是由互联网安全专家罗伯特·汉森和耶利米·格劳斯曼在 2008 年提出的。 是一种视觉欺骗手段，在 web 端就是 iframe 嵌套一个透明不可见的页面，让用户在不知情的情况下，点击攻击者想要欺骗用户点击的位置。”
点击劫持（ClickJacking）是一种视觉上的欺骗手段。大概有两种方式，一是攻击者使用一个透明的iframe，覆盖在一个网页上，然后诱使用户在该页面上进行操作，此时用户将在不知情的情况下点击透明的iframe页面；二是攻击者使用一张图片覆盖在网页，遮挡网页原有位置的含义；
1.DATA URI 释义:
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