2015年1月

两整数交换 异或实现

#include <stdio.h>

void swap(int a, int b);

int main(int argc, char *argv[]) {
    
    swap(1,2);
    return 0;
}

void swap(int a, int b)
{
    printf("%d  %d\n", a, b); // 1 2
    a = a^b;
    printf("%d  %d\n", a, b); // 3 2
    b = a^b;
    printf("%d  %d\n", a, b); // 3 1
    a = a^b;
    printf("%d  %d\n", a, b); // 2 1
}

HTTP Methods: GET vs. POST



The two most used HTTP methods are: GET and POST.


<h4>What is HTTP?</h4>

The Hypertext Transfer Protocol (HTTP) is designed to enable communications between clients and servers.

HTTP works as a request-response protocol between a client and server.

A web browser may be the client, and an application on a computer that hosts a web site may be the server.

Example: A client (browser) submits an HTTP request to the server; then the server returns a response to the client. The response contains status information about the request and may also contain the requested content.


<h4>Two HTTP Request Methods: GET and POST</h4>

Two commonly used methods for a request-response between a client and server are: GET and POST.

<h5>GET</h5>

Requests data from a specified resource

<h5>POST</h5>

Submits data to be processed to a specified resource

<h4>The GET Method</h4>
Note that query strings (name/value pairs) is sent in the URL of a GET request:

/test/demo_form.asp?name1=value1&name2=value2

<h5>Some other notes on GET requests:</h5>
<h5>GET</h5>

requests can be cached

requests remain in the browser history

requests can be bookmarked

requests should never be used when dealing with sensitive data

requests have length restrictions

requests should be used only to retrieve data

<h4>The POST Method</h4>
Note that query strings (name/value pairs) is sent in the HTTP message body of a POST request:

POST /test/demo_form.asp HTTP/1.1
Host: w3schools.com
name1=value1&name2=value2

<h5>Some other notes on POST requests:</h5>
<h5>POST</h5>

requests are never cached

requests do not remain in the browser history

requests cannot be bookmarked

requests requests have no restrictions on data length

<h4>Compare GET vs. POST</h4>
The following table compares the two HTTP methods: GET and POST.

GET POST
BACK button/Reload Harmless Data will be re-submitted (the browser should alert the user that the data are about to be re-submitted)
Bookmarked Can be bookmarked Cannot be bookmarked
Cached Can be cached Not cached
Encoding type application/x-www-form-urlencoded application/x-www-form-urlencoded or multipart/form-data. Use multipart encoding for binary data
History Parameters remain in browser history Parameters are not saved in browser history
Restrictions on data length Yes, when sending data, the GET method adds the data to the URL; and the length of a URL is limited (maximum URL length is 2048 characters) No restrictions
Restrictions on data type Only ASCII characters allowed No restrictions. Binary data is also allowed
Security GET is less secure compared to POST because data sent is part of the URL Never use GET when sending passwords or other sensitive information! POST is a little safer than GET because the parameters are not stored in browser history or in web server logs
Visibility Data is visible to everyone in the URL Data is not displayed in the URL