你如何用C++发出HTTP请求？

有没有办法轻松用C++发出HTTP请求？具体来说,我想下载页面的内容(API)并检查内容,看它是否包含1或0.是否也可以将内容下载到字符串中？

我有同样的问题.libcurl非常完整.当你要求一个C++库时,有一个C++包装器curlpp可能会让你感兴趣.neon是另一个有趣的C库,也支持WebDAV.

如果你使用C++,curlpp似乎很自然.源代码分发中提供了许多示例.要获取URL的内容,您可以执行类似的操作(从示例中提取):

// Edit : rewritten for cURLpp 0.7.3
// Note : namespace changed, was cURLpp in 0.7.2 ...

#include 
#include 

// RAII cleanup

curlpp::Cleanup myCleanup;

// Send request and get a result.
// Here I use a shortcut to get it in a string stream ...

std::ostringstream os;
os << curlpp::options::Url(std::string("http://www.wikipedia.org"));

string asAskedInQuestion = os.str();

查看curlpp源代码分发中的examples目录,有很多更复杂的情况,以及使用curlpp 的简单完整的最小情况.

我的2美分......

Windows代码:

#include 
#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;
#pragma comment(lib,"ws2_32.lib")




int main( void ){

WSADATA wsaData;
SOCKET Socket;
SOCKADDR_IN SockAddr;
int lineCount=0;
int rowCount=0;
struct hostent *host;
locale local;
char buffer[10000];
int i = 0 ;
int nDataLength;
string website_HTML;

// website url
string url = "www.google.com";

//HTTP GET
string get_http = "GET / HTTP/1.1\r\nHost: " + url + "\r\nConnection: close\r\n\r\n";


    if (WSAStartup(MAKEWORD(2,2), &wsaData) != 0){
        cout << "WSAStartup failed.\n";
        system("pause");
        //return 1;
    }

    Socket=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
    host = gethostbyname(url.c_str());

    SockAddr.sin_port=htons(80);
    SockAddr.sin_family=AF_INET;
    SockAddr.sin_addr.s_addr = *((unsigned long*)host->h_addr);

    if(connect(Socket,(SOCKADDR*)(&SockAddr),sizeof(SockAddr)) != 0){
        cout << "Could not connect";
        system("pause");
        //return 1;
    }

    // send GET / HTTP
    send(Socket,get_http.c_str(), strlen(get_http.c_str()),0 );

    // recieve html
    while ((nDataLength = recv(Socket,buffer,10000,0)) > 0){        
        int i = 0;
        while (buffer[i] >= 32 || buffer[i] == '\n' || buffer[i] == '\r'){

            website_HTML+=buffer[i];
            i += 1;
        }               
    }

    closesocket(Socket);
    WSACleanup();

    // Display HTML source 
    cout<

这是一个更好的实现: 

#include 
#include 
#include 

using std::string;

#pragma comment(lib,"ws2_32.lib")


HINSTANCE hInst;
WSADATA wsaData;
void mParseUrl(char *mUrl, string &serverName, string &filepath, string &filename);
SOCKET connectToServer(char *szServerName, WORD portNum);
int getHeaderLength(char *content);
char *readUrl2(char *szUrl, long &bytesReturnedOut, char **headerOut);


int main()
{
    const int bufLen = 1024;
    char *szUrl = "http://stackoverflow.com";
    long fileSize;
    char *memBuffer, *headerBuffer;
    FILE *fp;

    memBuffer = headerBuffer = NULL;

    if ( WSAStartup(0x101, &wsaData) != 0)
        return -1;


    memBuffer = readUrl2(szUrl, fileSize, &headerBuffer);
    printf("returned from readUrl\n");
    printf("data returned:\n%s", memBuffer);
    if (fileSize != 0)
    {
        printf("Got some data\n");
        fp = fopen("downloaded.file", "wb");
        fwrite(memBuffer, 1, fileSize, fp);
        fclose(fp);
         delete(memBuffer);
        delete(headerBuffer);
    }

    WSACleanup();
    return 0;
}


void mParseUrl(char *mUrl, string &serverName, string &filepath, string &filename)
{
    string::size_type n;
    string url = mUrl;

    if (url.substr(0,7) == "http://")
        url.erase(0,7);

    if (url.substr(0,8) == "https://")
        url.erase(0,8);

    n = url.find('/');
    if (n != string::npos)
    {
        serverName = url.substr(0,n);
        filepath = url.substr(n);
        n = filepath.rfind('/');
        filename = filepath.substr(n+1);
    }

    else
    {
        serverName = url;
        filepath = "/";
        filename = "";
    }
}

SOCKET connectToServer(char *szServerName, WORD portNum)
{
    struct hostent *hp;
    unsigned int addr;
    struct sockaddr_in server;
    SOCKET conn;

    conn = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (conn == INVALID_SOCKET)
        return NULL;

    if(inet_addr(szServerName)==INADDR_NONE)
    {
        hp=gethostbyname(szServerName);
    }
    else
    {
        addr=inet_addr(szServerName);
        hp=gethostbyaddr((char*)&addr,sizeof(addr),AF_INET);
    }

    if(hp==NULL)
    {
        closesocket(conn);
        return NULL;
    }

    server.sin_addr.s_addr=*((unsigned long*)hp->h_addr);
    server.sin_family=AF_INET;
    server.sin_port=htons(portNum);
    if(connect(conn,(struct sockaddr*)&server,sizeof(server)))
    {
        closesocket(conn);
        return NULL;
    }
    return conn;
}

int getHeaderLength(char *content)
{
    const char *srchStr1 = "\r\n\r\n", *srchStr2 = "\n\r\n\r";
    char *findPos;
    int ofset = -1;

    findPos = strstr(content, srchStr1);
    if (findPos != NULL)
    {
        ofset = findPos - content;
        ofset += strlen(srchStr1);
    }

    else
    {
        findPos = strstr(content, srchStr2);
        if (findPos != NULL)
        {
            ofset = findPos - content;
            ofset += strlen(srchStr2);
        }
    }
    return ofset;
}

char *readUrl2(char *szUrl, long &bytesReturnedOut, char **headerOut)
{
    const int bufSize = 512;
    char readBuffer[bufSize], sendBuffer[bufSize], tmpBuffer[bufSize];
    char *tmpResult=NULL, *result;
    SOCKET conn;
    string server, filepath, filename;
    long totalBytesRead, thisReadSize, headerLen;

    mParseUrl(szUrl, server, filepath, filename);

    ///////////// step 1, connect //////////////////////
    conn = connectToServer((char*)server.c_str(), 80);

    ///////////// step 2, send GET request /////////////
    sprintf(tmpBuffer, "GET %s HTTP/1.0", filepath.c_str());
    strcpy(sendBuffer, tmpBuffer);
    strcat(sendBuffer, "\r\n");
    sprintf(tmpBuffer, "Host: %s", server.c_str());
    strcat(sendBuffer, tmpBuffer);
    strcat(sendBuffer, "\r\n");
    strcat(sendBuffer, "\r\n");
    send(conn, sendBuffer, strlen(sendBuffer), 0);

//    SetWindowText(edit3Hwnd, sendBuffer);
    printf("Buffer being sent:\n%s", sendBuffer);

    ///////////// step 3 - get received bytes ////////////////
    // Receive until the peer closes the connection
    totalBytesRead = 0;
    while(1)
    {
        memset(readBuffer, 0, bufSize);
        thisReadSize = recv (conn, readBuffer, bufSize, 0);

        if ( thisReadSize <= 0 )
            break;

        tmpResult = (char*)realloc(tmpResult, thisReadSize+totalBytesRead);

        memcpy(tmpResult+totalBytesRead, readBuffer, thisReadSize);
        totalBytesRead += thisReadSize;
    }

    headerLen = getHeaderLength(tmpResult);
    long contenLen = totalBytesRead-headerLen;
    result = new char[contenLen+1];
    memcpy(result, tmpResult+headerLen, contenLen);
    result[contenLen] = 0x0;
    char *myTmp;

    myTmp = new char[headerLen+1];
    strncpy(myTmp, tmpResult, headerLen);
    myTmp[headerLen] = NULL;
    delete(tmpResult);
    *headerOut = myTmp;

    bytesReturnedOut = contenLen;
    closesocket(conn);
    return(result);
}

        
@JuanLuisSoldi我想你真的需要成为Windows开发人员才能欣赏这段代码的"美丽"...... 
我无法让curlpp工作,所以我使用了你的代码,谢谢 
美丽.这应该是公认的答案. 
@ Expanding-Dev只有MSVC(visual studio)理解"pragma评论".如果您使用其他任何东西,您必须手动链接"ws2_32.lib"(与任何其他库一样). 

3> Homer6..：
在Linux上,我尝试了cpp-netlib,libcurl,curlpp,urdl,boost :: asio并考虑了Qt(但根据许可证将其关闭).所有这些对于这种用途来说都是不完整的,有稀疏的接口,文档很差,没有维护或不支持https.

然后,根据/sf/ask/17360801/的建议,我尝试了POCO.哇,我希望我多年前见过.以下是发出HTTP GET请求的示例:

http://xjia.heroku.com/2011/09/10/learning-poco-get-with-http/

POCO是免费的,开源的(增强许可证).不,我与公司没有任何关系; 我真的很喜欢他们的界面.干得好(和女孩们).

http://pocoproject.org/download/index.html

希望这有助于某人...我花了三天时间尝试所有这些库.

        

4> huu..：
有一种更新的,不太成熟的卷曲包装器正在开发,称为C++请求.这是一个简单的GET请求:

#include 
#include 

int main(int argc, char** argv) {
    auto response = cpr::Get(cpr::Url{"http://httpbin.org/get"});
    std::cout << response.text << std::endl;
}


它支持各种HTTP动词和卷曲选项.还有更多的使用文档这里.

免责声明:我是这个库的维护者.

        
我昨天参加了你的CppCon 2015闪电演讲.做得好 - 谈话和图书馆.我特别喜欢"Curl for people"的设计理念. 
@Sossenbinder，如果您熟悉CMake，则可以使用该文件为该项目生成Visual Studio构建文件。[appveyor配置]（https://github.com/whoshuu/cpr/blob/3de75778fc225593281cba75b1a77a614d82618b/appveyor.yml）文件包含如何完成此操作的粗略示例。 
看起来不错,但构建是地狱,所以你的lib是没用的,我不能依赖包管理器(需要可靠的方法如何在外部添加deps)并且需要尽快使用功能库... 

5> FreeMemory..：
libCURL对你来说是个不错的选择.根据您的需要,教程应该告诉您您想要什么,特别是为了方便处理.但是,基本上,你可以这样做只是为了看到页面的来源:

CURL* c;
c = curl_easy_init();
curl_easy_setopt( c, CURL_URL, "www.google.com" );
curl_easy_perform( c );
curl_easy_cleanup( c );


我相信这会导致结果打印到标准输出.如果你想要处理它 - 我认为你做了 - 你需要设置CURL_WRITEFUNCTION.所有这些都包含在上面链接的卷曲教程中.

        

6> Marcelo Sant..：
如您所希望的C++解决方案,您可以使用Qt.它有一个你可以使用的QHttp类.

您可以查看文档:

http->setHost("qt.nokia.com");
http->get(QUrl::toPercentEncoding("/index.html"));


Qt还有更多可用于常见C++应用程序的内容.

        
我认为QHttp已被Qt 4.6及更高版本中的QNetworkAccessManager和相关类所取代. 
自Qt 4.4以来,已经记录了`QNetworkAccessManager`; 在Qt 4.8中说:`QHttp  - 这个类已经过时了.它用于保持旧的源代码工作.我们强烈建议不要在新代码中使用它.所以我猜它仍然可用,如果你忽略了已弃用的警告. 

7> Mark Lakata..：
这是我在cURL周围的最小包装器,只能将网页作为字符串获取.例如,这对于单元测试很有用.它基本上是围绕C代码的RAII包装器.

在您的机器上安装"libcurl" yum install libcurl libcurl-devel或同等产品.

用法示例:

CURLplusplus client;
string x = client.Get("http://google.com");
string y = client.Get("http://yahoo.com");


课程实施:

#include 


class CURLplusplus
{
private:
    CURL* curl;
    stringstream ss;
    long http_code;
public:
    CURLplusplus()
            : curl(curl_easy_init())
    , http_code(0)
    {

    }
    ~CURLplusplus()
    {
        if (curl) curl_easy_cleanup(curl);
    }
    std::string Get(const std::string& url)
    {
        CURLcode res;
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
        curl_easy_setopt(curl, CURLOPT_WRITEDATA, this);

        ss.str("");
        http_code = 0;
        res = curl_easy_perform(curl);
        if (res != CURLE_OK)
        {
            throw std::runtime_error(curl_easy_strerror(res));
        }
        curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
        return ss.str();
    }
    long GetHttpCode()
    {
        return http_code;
    }
private:
    static size_t write_data(void *buffer, size_t size, size_t nmemb, void *userp)
    {
        return static_cast(userp)->Write(buffer,size,nmemb);
    }
    size_t Write(void *buffer, size_t size, size_t nmemb)
    {
        ss.write((const char*)buffer,size*nmemb);
        return size*nmemb;
    }
};

        

8> 小智..：
您可能需要检查C++ REST SDK(代号为"Casablanca").http://msdn.microsoft.com/en-us/library/jj950081.aspx

使用C++ REST SDK,您可以更轻松地从C++应用程序连接到HTTP服务器.

用法示例:

#include 
#include 

using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features

int main(int argc, char** argv) {
    http_client client("http://httpbin.org/");

    http_response response;
    // ordinary `get` request
    response = client.request(methods::GET, "/get").get();
    std::cout << response.extract_string().get() << "\n";

    // working with json
    response = client.request(methods::GET, "/get").get();
    std::cout << "url: " << response.extract_json().get()[U("url")] << "\n";
}


C++ REST SDK是一个Microsoft项目,使用现代异步C++ API设计在本机代码中进行基于云的客户端 - 服务器通信.

        

9> Vinz..：
有了这个答案,我将参考Software_Developer的答案.通过重建代码,我发现某些部分已被弃用(gethostbyname())或者没有为操作提供错误处理(创建套接字,发送内容).

以下Windows代码使用Visual Studio 2013和Windows 8.1 64位以及Windows 7 64位进行测试.它将以www.google.com的Web服务器为目标进行IPv4 TCP连接.

#include 
#include 
#include 
#include 
#pragma comment(lib,"ws2_32.lib")
using namespace std;
    int main (){
    // Initialize Dependencies to the Windows Socket.
    WSADATA wsaData;
    if (WSAStartup(MAKEWORD(2,2), &wsaData) != 0) {
        cout << "WSAStartup failed.\n";
        system("pause");
        return -1;
    }

    // We first prepare some "hints" for the "getaddrinfo" function
    // to tell it, that we are looking for a IPv4 TCP Connection.
    struct addrinfo hints;
    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;          // We are targeting IPv4
    hints.ai_protocol = IPPROTO_TCP;    // We are targeting TCP
    hints.ai_socktype = SOCK_STREAM;    // We are targeting TCP so its SOCK_STREAM

    // Aquiring of the IPv4 address of a host using the newer
    // "getaddrinfo" function which outdated "gethostbyname".
    // It will search for IPv4 addresses using the TCP-Protocol.
    struct addrinfo* targetAdressInfo = NULL;
    DWORD getAddrRes = getaddrinfo("www.google.com", NULL, &hints, &targetAdressInfo);
    if (getAddrRes != 0 || targetAdressInfo == NULL)
    {
        cout << "Could not resolve the Host Name" << endl;
        system("pause");
        WSACleanup();
        return -1;
    }

    // Create the Socket Address Informations, using IPv4
    // We dont have to take care of sin_zero, it is only used to extend the length of SOCKADDR_IN to the size of SOCKADDR
    SOCKADDR_IN sockAddr;
    sockAddr.sin_addr = ((struct sockaddr_in*) targetAdressInfo->ai_addr)->sin_addr;    // The IPv4 Address from the Address Resolution Result
    sockAddr.sin_family = AF_INET;  // IPv4
    sockAddr.sin_port = htons(80);  // HTTP Port: 80

    // We have to free the Address-Information from getaddrinfo again
    freeaddrinfo(targetAdressInfo);

    // Creation of a socket for the communication with the Web Server,
    // using IPv4 and the TCP-Protocol
    SOCKET webSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (webSocket == INVALID_SOCKET)
    {
        cout << "Creation of the Socket Failed" << endl;
        system("pause");
        WSACleanup();
        return -1;
    }

    // Establishing a connection to the web Socket
    cout << "Connecting...\n";
    if(connect(webSocket, (SOCKADDR*)&sockAddr, sizeof(sockAddr)) != 0)
    {
        cout << "Could not connect";
        system("pause");
        closesocket(webSocket);
        WSACleanup();
        return -1;
    }
    cout << "Connected.\n";

    // Sending a HTTP-GET-Request to the Web Server
    const char* httpRequest = "GET / HTTP/1.1\r\nHost: www.google.com\r\nConnection: close\r\n\r\n";
    int sentBytes = send(webSocket, httpRequest, strlen(httpRequest),0);
    if (sentBytes < strlen(httpRequest) || sentBytes == SOCKET_ERROR)
    {
        cout << "Could not send the request to the Server" << endl;
        system("pause");
        closesocket(webSocket);
        WSACleanup();
        return -1;
    }

    // Receiving and Displaying an answer from the Web Server
    char buffer[10000];
    ZeroMemory(buffer, sizeof(buffer));
    int dataLen;
    while ((dataLen = recv(webSocket, buffer, sizeof(buffer), 0) > 0))
    {
        int i = 0;
        while (buffer[i] >= 32 || buffer[i] == '\n' || buffer[i] == '\r') {
            cout << buffer[i];
            i += 1;
        }
    }

    // Cleaning up Windows Socket Dependencies
    closesocket(webSocket);
    WSACleanup();

    system("pause");
    return 0;
}


参考文献:

gethostbyname的弃用

socket()的返回值

send()的返回值

        

10> sybreon..：
C++没有提供任何直接的方法.它完全取决于您拥有的平台和库.

在最坏的情况下,您可以使用boost :: asio库建立TCP连接,发送HTTP头(RFC 2616),并直接解析响应.看看您的应用程序需求,这很简单.