1、背景

在实际项目开发中，服务端有可能提供域名或者ip地址，在提供域名时，则需要通过域名获取到真实的ip地址。

同时考虑到代码的兼容性，因此代码需在linux和windows环境下均可运行。

2、demo

#include <iostream>
#include <string.h>
#include <string>

#if defined(__GNUC__)
#include <arpa/inet.h>
#include <resolv.h>
#include <netdb.h>
#elif defined(_MSC_VER)
#include <WinSock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib") // 连接库
#endif

int main()
{
	const char* hostname = "www.ds.com";
#if defined(__GNUC__)
	// 初始化一个hostent结构体用于存储DNS查询结果
	struct hostent* result = gethostbyname(hostname);
	if (result == nullptr)
	{
		return 1;
	}

	in_addr* addr_list = reinterpret_cast<in_addr*>(result->h_addr_list[0]);
	char* ip = inet_ntoa(addr_list[0]);
	std::string str_ip(ip, strlen(ip));
	std::cout << "IP address: " << str_ip << std::endl;

#elif defined(_MSC_VER)
	WSADATA wsaData;
	WSAStartup(MAKEWORD(2, 2), &wsaData);

	struct addrinfo hints, * res;
	memset(&hints, 0, sizeof hints);
	hints.ai_family = AF_INET; // ipv4
	hints.ai_socktype = SOCK_STREAM;

	if (getaddrinfo(hostname, NULL, &hints, &res) != 0)
	{
		std::cerr << "get addr info failed" << std::endl;
		WSACleanup();

		Sleep(3000);
		return 1;
	}

	struct sockaddr_in* ipv4 = (struct sockaddr_in*)res->ai_addr;
	char ipStr[INET_ADDRSTRLEN];
	inet_ntop(AF_INET, &ipv4->sin_addr, ipStr, INET_ADDRSTRLEN);
	std::cout << "IP address: " << ipStr << std::endl;

	freeaddrinfo(res); // 释放getaddrinfo分配的资源
	WSACleanup(); // 清理WSA环境
#endif

	return 0;
}