方法一：

• windows下调用icmp.dll库，实现ping连通检测，缺点是不能跨平台，受限于icmp.dll库：

// windows下调用icmp.dll库实现网络连通检测示例代码#include <Winsock2.h>
#include <iphlpapi.h>
#include <stdio.h>#pragma comment(lib,"Iphlpapi.lib")
#pragma comment(lib,"Ws2_32.lib")
typedef HANDLE (WINAPI* ICMPCREATEFILE)(VOID);
typedef BOOL (WINAPI* ICMPCLOSEHANDLE)(HANDLE);
typedef DWORD (WINAPI* ICMPSENDECHO)(HANDLE, DWORD, LPVOID, WORD,PIP_OPTION_INFORMATION, LPVOID, DWORD, DWORD);    // 定义三个指针函数
ICMPCREATEFILE pIcmpCreateFile;
ICMPCLOSEHANDLE pIcmpCloseHandle;
ICMPSENDECHO pIcmpSendEcho; // 函数功能：初始化ICMP函数：
BOOL InitIcmp()
{   HINSTANCE hIcmp = LoadLibrary(TEXT("ICMP.DLL"));    // 需自行下载icmp.dll动态库if(hIcmp==NULL){   return false; }  pIcmpCreateFile = (ICMPCREATEFILE)GetProcAddress(hIcmp,"IcmpCreateFile");   pIcmpCloseHandle = (ICMPCLOSEHANDLE)GetProcAddress(hIcmp,"IcmpCloseHandle");   pIcmpSendEcho = (ICMPSENDECHO)GetProcAddress(hIcmp,"IcmpSendEcho");   if ((pIcmpCreateFile == NULL)||(pIcmpCloseHandle == NULL)||(pIcmpSendEcho == NULL))   return false;   return true;
}// 函数功能：判断是否能ping通IP
// 函数参数：IP地址或域名
BOOL ICMPPing(char* host)
{   DWORD timeOut=1000;                                    // 设置超时   ULONG hAddr=inet_addr(host);                           // 如果是IP地址就直接转换   if(hAddr==INADDR_NONE)   {   hostent* hp=gethostbyname(host);                   // 如果是域名就用DNS解析出IP地址   if(hp)   memcpy(&hAddr,hp->h_addr_list,hp->h_length);   // IP地址   else{   return false;   }   }   HANDLE hIp=pIcmpCreateFile();   IP_OPTION_INFORMATION ipoi;   memset(&ipoi,0,sizeof(IP_OPTION_INFORMATION));   ipoi.Ttl =128;                  //Time-To-Live   unsigned char pSend[36];                               // 发送包   memset(pSend,'E',32);   int repSize=sizeof(ICMP_ECHO_REPLY)+32;   unsigned char pReply[100];                             // 接收包   ICMP_ECHO_REPLY* pEchoReply=(ICMP_ECHO_REPLY*)pReply;   DWORD nPackets=pIcmpSendEcho(hIp,hAddr,pSend,32,&ipoi,pReply,repSize,timeOut);    // 发送ICMP数据报文   if(pEchoReply->Status!=0)             // 超时，可能是主机禁用了ICMP 或者目标主机不存在  {   pIcmpCloseHandle(hIp);   return false;   }   pIcmpCloseHandle(hIp);   return true;
}
int main()
{InitIcmp();if (true == ICMPPing("127.0.0.1")){printf("OK.\n");}else{printf("NOT.\n");}system("pause");return 0;
}

方法二：

• 使用原始套接字，模拟实现ping程序以进行网络连通检测，可跨平台，缺点是在linux下使用原始套接字必须拥有超级用户权限：

// 模拟实现ping程序，跨平台检测网络连接#ifdef _WIN32
#include <WinSock2.h>
#pragma comment(lib, "WS2_32")struct WindowsSocketLibInit
{WindowsSocketLibInit(){WSADATA wsaData;WORD sockVersion = MAKEWORD(2, 2);WSAStartup(sockVersion, &wsaData);}~WindowsSocketLibInit(){WSACleanup();}
} INITSOCKETGLOBALVARIABLE;
#else
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <ctime>
#include <cstdlib>
#include <cstdint>
#include <cstring>
#endif#include <string>
#include <limits>unsigned short getChecksum(unsigned short *buff, unsigned size);bool ping(std::string ip)
{static unsigned INDEX = 0;const unsigned IP_HEADER_LENGTH = 20;const unsigned FILL_LENGTH = 32;struct IcmpHdr{unsigned char icmpType;unsigned char icmpCode;unsigned short icmpChecksum;unsigned short icmpId;unsigned short icmpSequence;};int socketFd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);int timeoutTick = 200;setsockopt(socketFd, SOL_SOCKET, SO_RCVTIMEO, (char *)&timeoutTick, sizeof(timeoutTick));sockaddr_in des = {AF_INET, htons(0)};des.sin_addr.s_addr = inet_addr(ip.c_str());char buff[sizeof(IcmpHdr) + FILL_LENGTH] = {0};IcmpHdr *pIcmpHdr = (IcmpHdr *)(buff);unsigned short id = std::rand() % (std::numeric_limits<unsigned short>::max)();pIcmpHdr->icmpType = 8;std::cout << "---" << pIcmpHdr->icmpType << std::endl;pIcmpHdr->icmpCode = 0;pIcmpHdr->icmpId = id;pIcmpHdr->icmpSequence = INDEX++;std::memcpy(&buff[sizeof(IcmpHdr)], "TestTest", sizeof("TestTest"));pIcmpHdr->icmpChecksum = getChecksum((unsigned short *)buff, sizeof(buff));if (-1 == sendto(socketFd, buff, sizeof(buff), 0, (sockaddr *)&des, sizeof(des))){return false;}char recv[1 << 10];int ret = recvfrom(socketFd, recv, sizeof(recv), 0, NULL, NULL);if (-1 == ret || ret < IP_HEADER_LENGTH + sizeof(IcmpHdr)){return false;}IcmpHdr *pRecv = (IcmpHdr *)(recv + IP_HEADER_LENGTH);return !(pRecv->icmpType != 0 || pRecv->icmpId != id);
}unsigned short getChecksum(unsigned short *buff, unsigned size)
{unsigned long ret = 0;for (unsigned i = 0; i < size; i += sizeof(unsigned short)){ret += *buff++;}if (size & 1){ret += *(unsigned char *)buff;}ret = (ret >> 16) + (ret & 0xFFFF);ret += ret >> 16;return (unsigned short)~ret;
}

方法三：

• 使用非阻塞connect函数和select定时相结合来检测网络连通，可跨平台，以下为windows下实现代码：

// 使用非阻塞connect和select定时检测解决connect失败时阻塞时间过长的问题#include <stdio.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")  int main()
{  // 网络初始化  WORD wVersionRequested;  WSADATA wsaData;  wVersionRequested = MAKEWORD(2, 2);  WSAStartup( wVersionRequested, &wsaData );  // 创建客户端socket(默认为是阻塞socket)  SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0);  // 设置为非阻塞的socket  int iMode = 1;  ioctlsocket(sockClient, FIONBIO, (u_long FAR*)&iMode);   // 定义服务端  SOCKADDR_IN addrSrv;  addrSrv.sin_addr.S_un.S_addr = inet_addr("192.168.26.67");  addrSrv.sin_family = AF_INET;  addrSrv.sin_port = htons(31800);  // 超时时间  struct timeval tm;  tm.tv_sec  = 0;  tm.tv_usec = 5000;  int ret = -1;  // 尝试去连接服务端  if (-1 != connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR)))  {  ret = 1; // 连接成功  }  else  {  fd_set set;  FD_ZERO(&set);  FD_SET(sockClient, &set);  if (select(-1, NULL, &set, NULL, &tm) <= 0)  {  ret = -1; // 有错误(select错误或者超时)  }  else  {  int error = -1;  int optLen = sizeof(int);  getsockopt(sockClient, SOL_SOCKET, SO_ERROR, (char*)&error, &optLen);   // 之所以下面的程序不写成三目运算符的形式， 是为了更直观， 便于注释  if (0 != error)  {  ret = -1; // 有错误  }  else  {  ret = 1;  // 无错误  }  }  }  // 设回为阻塞socket  iMode = 0;  ioctlsocket(sockClient, FIONBIO, (u_long FAR*)&iMode); //设置为阻塞模式  // connect状态  if (-1 == ret) {printf("error\n");} else if (1 == ret) {printf("success");}//printf("ret is %d\n", ret);  // 发送数据到服务端测试以下  if(1 == ret)  {  send(sockClient, "hello world", strlen("hello world") + 1, 0);  }  // 释放网络连接  closesocket(sockClient);  WSACleanup();  getchar();return 0;
}  

方法四：

• 使用setsockopt函数设定socket连接、接收和发送的响应时间，可以通过connect之前设定SO_SNDTIMO来达到控制连接超时的目的：

// 自行添加相应头文件int main(int argc, char *argv[])
{int fd;struct sockaddr_in addr;struct timeval timeo = {3, 0};socklen_t len = sizeof(timeo);fd = socket(AF_INET, SOCK_STREAM, 0);  if (argc == 4)  timeo.tv_sec = atoi(argv[3]);  setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &timeo, len);  addr.sin_family = AF_INET;  addr.sin_addr.s_addr = inet_addr(argv[1]);  addr.sin_port = htons(atoi(argv[2]));  if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {  if (errno == EINPROGRESS) {  fprintf(stderr, "timeout/n");  return -1;  }         perror("connect");  return 0;  }         printf("connected/n");  return 0;
}

方法五：

• linux下直接调用执行ping子程序以实现检测网络连通功能：

// 自行添加相应代码文件int go_ping(char *svrip)
{int i = 0;while(i < 3){pid_t pid;if ((pid = vfork()) < 0) {printf("vfork error");exit(1);} else if (pid == 0) {if ( execlp("ping", "ping","-c 1",svrip, (char*)0) < 0){printf("execlp error\n");exit(1);}}int stat;waitpid(pid, &stat, 0);if (stat == 0){return 0;}sleep(3);i++;}return -1;
}

参考资料：

• http://www.imooc.com/wenda/detail/443658
• https://blog.csdn.net/qq_30650153/article/details/86244309
• https://www.jianshu.com/p/95515d39897c
• http://bbs.chinaunix.net/thread-2076080-1-1.html
• https://blog.csdn.net/hj605635529/article/details/74157305