手把手教你写基于C++ Winsock的图片下载的网络爬虫
先来说一下主要的技术点:
1. 输入起始网址,使用ssacnf函数解析出主机号和路径(仅处理http协议网址)
2. 使用socket套接字连接服务器,,获取网页html代码(使用http协议的GET请求),然后使用正则表达式解析出图片url和其他的url。
3. 下载图片至创建的文件夹中,同时其他的url push进队列。
4. 为了使爬虫能够连续的工作,这里使用了BFS宽度优先搜索,也就是说一开始输入的网址作为起始网址,push进队列,然后把能解析出来的网址在不重复的情况下都push进队列,每次取队列的top来执行下载操作,直到队列为空时终止。
下面附上技术点的学习资料供参考:
ssanf函数的用法:
http://www.cnblogs.com/mycapple/archive/2012/08/03/2621681.html
C++11正则表达式
http://blog.sina.com.cn/s/blog_ac9fdc0b0101oow9.html
http协议:
http://www.ucai.cn/course/show/234
Socket编程:
http://blog.csdn.net/nk_test/article/details/47756381
http://blog.csdn.net/nk_test/article/details/47733307
另外,这个小爬虫结构简陋,还存在很多不足,例如队列中的url太多会爆内存,正则表达式匹配不够准确等,仅仅适合大家学习的时候练手哈。也欢迎大家发现bug,给出好的建议。
- /*下载图片 C++ Winsock 网络编程*/
#define _CRT_SECURE_NO_WARNINGS //vs 2013用于忽略c语言安全性警告
#include <cstdio>
#include <iostream>
#include <fstream>
#include <string>
#include <cstring>
#include <regex>
#include <vector>
#include <queue>
#include <algorithm>
#include <winsock2.h>
#include <map>
using namespace std;
#pragma comment(lib, "ws2_32.lib")
char host[500];
int num = 1;
char othPath[800];
string allHtml;
vector <string> photoUrl;
vector <string> comUrl;
map <string, int> mp; //防止相同网址重复遍历
SOCKET sock;
bool analyUrl(char *url) //仅支持http协议,解析出主机和IP地址
{
char *pos = strstr(url, "http://");
if (pos == NULL)
return false;
else
pos += 7;
sscanf(pos, "%[^/]%s", host, othPath); //http:// 后一直到/之前的是主机名
cout << "host: " << host << " repath:" << othPath << endl;
return true;
}
void regexGetimage(string &allHtml) //C++11 正则表达式提取图片url
{
smatch mat;
regex pattern("src=\"(.*?\.jpg)\"");
string::const_iterator start = allHtml.begin();
string::const_iterator end = allHtml.end();
while (regex_search(start, end, mat, pattern))
{
string msg(mat[1].first, mat[1].second);
photoUrl.push_back(msg);
start = mat[0].second;
}
}
void regexGetcom(string &allHtml) //提取网页中的http://的url
{
smatch mat;
//regex pattern("href=\"(.*?\.html)\"");
regex pattern("href=\"(http://[^\s'\"]+)\"");
string::const_iterator start = allHtml.begin();
string::const_iterator end = allHtml.end();
while (regex_search(start, end, mat, pattern))
{
string msg(mat[1].first, mat[1].second);
comUrl.push_back(msg);
start = mat[0].second;
}
}
void preConnect() //socket进行网络连接
{
WSADATA wd;
WSAStartup(MAKEWORD(2, 2), &wd);
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET)
{
cout << "建立socket失败! 错误码: " << WSAGetLastError() << endl;
return;
}
sockaddr_in sa = { AF_INET };
int n = bind(sock, (sockaddr*)&sa, sizeof(sa));
if (n == SOCKET_ERROR)
{
cout << "bind函数失败! 错误码: " << WSAGetLastError() << endl;
return;
}
struct hostent *p = gethostbyname(host);
if (p == NULL)
{
cout << "主机无法解析出ip! 错误吗: " << WSAGetLastError() << endl;
return;
}
sa.sin_port = htons(80);
memcpy(&sa.sin_addr, p->h_addr, 4);// with some problems ???
//sa.sin_addr.S_un.S_addr = inet_addr(*(p->h_addr_list));
//cout << *(p->h_addr_list) << endl;
n = connect(sock, (sockaddr*)&sa, sizeof(sa));
if (n == SOCKET_ERROR)
{
cout << "connect函数失败! 错误码: " << WSAGetLastError() << endl;
return;
}
//像服务器发送GET请求,下载图片
string reqInfo = "GET " +(string)othPath+ " HTTP/1.1\r\nHost: " + (string)host + "\r\nConnection:Close\r\n\r\n";
if (SOCKET_ERROR == send(sock, reqInfo.c_str(), reqInfo.size(), 0))
{
cout << "send error! 错误码: " << WSAGetLastError() << endl;
closesocket(sock);
return;
}
//PutImagtoSet();
}
void OutIamge(string imageUrl) //将图片命名,保存在目录下
{
int n;
char temp[800];
strcpy(temp, imageUrl.c_str());
analyUrl(temp);
preConnect();
string photoname;
photoname.resize(imageUrl.size());
int k = 0;
for (int i = 0; i<imageUrl.length(); i++){
char ch = imageUrl[i];
if (ch != '\\'&&ch != '/'&&ch != ':'&&ch != '*'&&ch != '?'&&ch != '"'&&ch != '<'&&ch != '>'&&ch != '|')
photoname[k++] = ch;
}
photoname = "./img/"+photoname.substr(0, k) + ".jpg";
fstream file;
file.open(photoname, ios::out | ios::binary);
char buf[1024];
memset(buf, 0, sizeof(buf));
n = recv(sock, buf, sizeof(buf)-1, 0);
char *cpos = strstr(buf, "\r\n\r\n");
//allHtml = "";
//allHtml += string(cpos);
file.write(cpos + strlen("\r\n\r\n"), n - (cpos - buf) - strlen("\r\n\r\n"));
while ((n = recv(sock, buf, sizeof(buf)-1, 0)) > 0)
{
file.write(buf, n);
//buf[n] = '\0';
//allHtml += string(buf);
}
//file.write(allHtml.c_str(), allHtml.length());
file.close();
//closesocket(sock);
}
void PutImagtoSet() //解析整个html代码
{
int n;
//preConnect();
char buf[1024];
while ((n = recv(sock, buf, sizeof(buf)-1, 0)) > 0)
{
buf[n] = '\0';
allHtml += string(buf);
}
regexGetimage(allHtml);
regexGetcom(allHtml);
}
void bfs(string beginUrl) //宽度优先搜索,像爬虫一样遍历网页
{
queue<string> q;
q.push(beginUrl);
while (!q.empty())
{
string cur = q.front();
mp[cur]++;
q.pop();
char tmp[800];
strcpy(tmp, cur.c_str());
analyUrl(tmp);
preConnect();
PutImagtoSet();
vector<string>::iterator ita = photoUrl.begin();
for (ita; ita != photoUrl.end(); ++ita)
{
OutIamge(*ita);
}
photoUrl.clear();
vector <string>::iterator it = comUrl.begin();
for (it; it != comUrl.end(); ++it)
{
if (mp[*it]==0)
q.push(*it);
}
comUrl.clear();
}
}
int main()
{
CreateDirectoryA("./img", 0); //在工程下创建文件夹
string beginUrl= "http://news.qq.com/"; //输入起始网址
bfs(beginUrl);
return 0;
}
效果图: