libcurl库的简介（一）

一、Libcurl库简介

LibCurl是免费的客户端URL传输库，支持FTP,FTPS, HTTP, HTTPS, SCP, SFTP, TFTP, TELNET, DICT, FILE ，LDAP等协议，其主页是http://curl.haxx.se/。

• 具备线程安全
• 与IPv6兼容

二、libcurl库函数部分介绍

1.       调用curl_global_init()初始化libcurl

　　CURL_EXTERN CURLcode curl_global_init(long flags);

2.       调用 curl_easy_init()函数得到 easy interface型指针

　　CURL_EXTERN CURL *curl_easy_init(void);

3.       调用curl_easy_setopt设置传输选项，实现回调函数以完成用户特定任务

　　此函数详情请看：https://curl.haxx.se/libcurl/c/curl_easy_setopt.html

　　CURL_EXTERN CURLcode curl_easy_setopt(CURL *curl, CURLoption option, ...);

　　BEHAVIOR OPTIONS：

　　CURLOPT_VERBOSE

　　Display verbose information. See CURLOPT_VERBOSE

　　CURLOPT_HEADER

　　Include the header in the body output. See CURLOPT_HEADER

　　CURLOPT_NOPROGRESS

　　Shut off the progress meter. See CURLOPT_NOPROGRESS

　　CURLOPT_NOSIGNAL

　　Do not install signal handlers. See CURLOPT_NOSIGNAL

　　CURLOPT_WILDCARDMATCH

　　Transfer multiple files according to a file name pattern. See CURLOPT_WILDCARDMATCH

　　CALLBACK OPTIONS：

　　CURLOPT_WRITEFUNCTION

　　Callback for writing data. See CURLOPT_WRITEFUNCTION

　　#include <curl/curl.h>

  size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);
  CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);

　　详细：https://curl.haxx.se/libcurl/c/CURLOPT_WRITEFUNCTION.html

　　CURLOPT_WRITEDATA

　　Data pointer to pass to the write callback. See CURLOPT_WRITEDATA

　　eg:CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEDATA, void *pointer);

　　CURLOPT_READFUNCTION

　　Callback for reading data. See CURLOPT_READFUNCTION

　　size_t read_callback(char *buffer, size_t size, size_t nitems, void *userdata);

　　CURLcode curl_easy_setopt(CURL *handle, CURLOPT_READFUNCTION, read_callback);

　　CURLOPT_READDATA

　　Data pointer to pass to the read callback. See CURLOPT_READDATA

　　CURLOPT_IOCTLFUNCTION

　　Callback for I/O operations. See CURLOPT_IOCTLFUNCTION

　　CURLOPT_IOCTLDATA

　　Data pointer to pass to the I/O callback. See CURLOPT_IOCTLDATA

　　CURLOPT_SEEKFUNCTION

　　Callback for seek operations. See CURLOPT_SEEKFUNCTION

　　CURLOPT_SEEKDATA

　　Data pointer to pass to the seek callback. See CURLOPT_SEEKDATA

　　CURLOPT_SOCKOPTFUNCTION

　　Callback for sockopt operations. See CURLOPT_SOCKOPTFUNCTION

　　CURLOPT_SOCKOPTDATA

　　Data pointer to pass to the sockopt callback. See CURLOPT_SOCKOPTDATA

　　CURLOPT_OPENSOCKETFUNCTION

　　Callback for socket creation. See CURLOPT_OPENSOCKETFUNCTION

　　CURLOPT_OPENSOCKETDATA

　　Data pointer to pass to the open socket callback. See CURLOPT_OPENSOCKETDATA

　　CURLOPT_CLOSESOCKETFUNCTION

　　Callback for closing socket. See CURLOPT_CLOSESOCKETFUNCTION

　　CURLOPT_CLOSESOCKETDATA

　　Data pointer to pass to the close socket callback. See CURLOPT_CLOSESOCKETDATA

　　CURLOPT_PROGRESSFUNCTION

　　OBSOLETE callback for progress meter. See CURLOPT_PROGRESSFUNCTION

　　CURLOPT_PROGRESSDATA

　　Data pointer to pass to the progress meter callback. See CURLOPT_PROGRESSDATA

　　CURLOPT_XFERINFOFUNCTION

　　Callback for progress meter. See CURLOPT_XFERINFOFUNCTION

　　CURLOPT_XFERINFODATA

　　Data pointer to pass to the progress meter callback. See CURLOPT_XFERINFODATA

　　CURLOPT_HEADERFUNCTION

　　Callback for writing received headers. See CURLOPT_HEADERFUNCTION

　　CURLOPT_HEADERDATA

　　Data pointer to pass to the header callback. See CURLOPT_HEADERDATA

　　CURLOPT_DEBUGFUNCTION

　　Callback for debug information. See CURLOPT_DEBUGFUNCTION

　　CURLOPT_DEBUGDATA

　　Data pointer to pass to the debug callback. See CURLOPT_DEBUGDATA

　　CURLOPT_SSL_CTX_FUNCTION

　　Callback for SSL context logic. See CURLOPT_SSL_CTX_FUNCTION

　　CURLOPT_SSL_CTX_DATA

　　Data pointer to pass to the SSL context callback. See CURLOPT_SSL_CTX_DATA

　　CURLOPT_CONV_TO_NETWORK_FUNCTION

　　Callback for code base conversion. See CURLOPT_CONV_TO_NETWORK_FUNCTION

　　CURLOPT_CONV_FROM_NETWORK_FUNCTION

　　Callback for code base conversion. See CURLOPT_CONV_FROM_NETWORK_FUNCTION

　　CURLOPT_CONV_FROM_UTF8_FUNCTION

　　Callback for code base conversion. See CURLOPT_CONV_FROM_UTF8_FUNCTION

　　CURLOPT_INTERLEAVEFUNCTION

　　Callback for RTSP interleaved data. See CURLOPT_INTERLEAVEFUNCTION

　　CURLOPT_INTERLEAVEDATA

　　Data pointer to pass to the RTSP interleave callback. See CURLOPT_INTERLEAVEDATA

　　CURLOPT_CHUNK_BGN_FUNCTION

　　Callback for wildcard download start of chunk. See CURLOPT_CHUNK_BGN_FUNCTION

　　CURLOPT_CHUNK_END_FUNCTION

　　Callback for wildcard download end of chunk. See CURLOPT_CHUNK_END_FUNCTION

　　CURLOPT_CHUNK_DATA

　　Data pointer to pass to the chunk callbacks. See CURLOPT_CHUNK_DATA

　　CURLOPT_FNMATCH_FUNCTION

　　Callback for wildcard matching. See CURLOPT_FNMATCH_FUNCTION

　　CURLOPT_FNMATCH_DATA

　　Data pointer to pass to the wildcard matching callback. See CURLOPT_FNMATCH_DATA

　　CURLOPT_SUPPRESS_CONNECT_HEADERS

　　Suppress proxy CONNECT response headers from user callbacks. See CURLOPT_SUPPRESS_CONNECT_HEADERS

　　CURLOPT_RESOLVER_START_FUNCTION

　　Callback to be called before a new resolve request is started. See CURLOPT_RESOLVER_START_FUNCTION

　　CURLOPT_RESOLVER_START_DATA

　　Data pointer to pass to resolver start callback. See CURLOPT_RESOLVER_START_DATA

　　HTTP OPTIONS：

　　CURLOPT_AUTOREFERER

　　Automatically set Referer: header. See CURLOPT_AUTOREFERER

　　CURLOPT_ACCEPT_ENCODING

　　Accept-Encoding and automatic decompressing data. See CURLOPT_ACCEPT_ENCODING

　　CURLOPT_TRANSFER_ENCODING

　　Request Transfer-Encoding. See CURLOPT_TRANSFER_ENCODING

　　CURLOPT_FOLLOWLOCATION

　　Follow HTTP redirects. See CURLOPT_FOLLOWLOCATION

　　CURLOPT_UNRESTRICTED_AUTH

　　Do not restrict authentication to original host. CURLOPT_UNRESTRICTED_AUTH

　　CURLOPT_MAXREDIRS

　　Maximum number of redirects to follow. See CURLOPT_MAXREDIRS

　　CURLOPT_POSTREDIR

　　How to act on redirects after POST. See CURLOPT_POSTREDIR

　　CURLOPT_PUT

　　Issue an HTTP PUT request. See CURLOPT_PUT

　　CURLOPT_POST

　　Issue an HTTP POST request. See CURLOPT_POST

　　CURLOPT_POSTFIELDS

　　Send a POST with this data. See CURLOPT_POSTFIELDS

　　CURLOPT_POSTFIELDSIZE

　　The POST data is this big. See CURLOPT_POSTFIELDSIZE

　　CURLOPT_POSTFIELDSIZE_LARGE

　　The POST data is this big. See CURLOPT_POSTFIELDSIZE_LARGE

　　CURLOPT_COPYPOSTFIELDS

　　Send a POST with this data - and copy it. See CURLOPT_COPYPOSTFIELDS

　　CURLOPT_HTTPPOST

　　Multipart formpost HTTP POST. See CURLOPT_HTTPPOST

　　CURLOPT_REFERER

　　Referer: header. See CURLOPT_REFERER

　　CURLOPT_USERAGENT

　　User-Agent: header. See CURLOPT_USERAGENT

　　CURLOPT_HTTPHEADER

　　Custom HTTP headers. See CURLOPT_HTTPHEADER

　　CURLOPT_HEADEROPT

　　Control custom headers. See CURLOPT_HEADEROPT

　　CURLOPT_PROXYHEADER

　　Custom HTTP headers sent to proxy. See CURLOPT_PROXYHEADER

　　CURLOPT_HTTP200ALIASES

　　Alternative versions of 200 OK. See CURLOPT_HTTP200ALIASES

　　CURLOPT_COOKIE

　　Cookie(s) to send. See CURLOPT_COOKIE

　　CURLOPT_COOKIEFILE

　　File to read cookies from. See CURLOPT_COOKIEFILE

　　CURLOPT_COOKIEJAR

　　File to write cookies to. See CURLOPT_COOKIEJAR

　　CURLOPT_COOKIESESSION

　　Start a new cookie session. See CURLOPT_COOKIESESSION

　　CURLOPT_COOKIELIST

　　Add or control cookies. See CURLOPT_COOKIELIST

　　CURLOPT_HTTPGET

　　Do an HTTP GET request. See CURLOPT_HTTPGET

　　CURLOPT_REQUEST_TARGET

　　Set the request target. CURLOPT_REQUEST_TARGET

　　CURLOPT_HTTP_VERSION

　　HTTP version to use. CURLOPT_HTTP_VERSION

　　CURLOPT_IGNORE_CONTENT_LENGTH

　　Ignore Content-Length. See CURLOPT_IGNORE_CONTENT_LENGTH

　　CURLOPT_HTTP_CONTENT_DECODING

　　Disable Content decoding. See CURLOPT_HTTP_CONTENT_DECODING

　　CURLOPT_HTTP_TRANSFER_DECODING

　　Disable Transfer decoding. See CURLOPT_HTTP_TRANSFER_DECODING

　　CURLOPT_EXPECT_100_TIMEOUT_MS

　　100-continue timeout. See CURLOPT_EXPECT_100_TIMEOUT_MS

　　CURLOPT_PIPEWAIT

　　Wait on connection to pipeline on it. See CURLOPT_PIPEWAIT

　　CURLOPT_STREAM_DEPENDS

　　This HTTP/2 stream depends on another. See CURLOPT_STREAM_DEPENDS

　　CURLOPT_STREAM_DEPENDS_E

　　This HTTP/2 stream depends on another exclusively. See CURLOPT_STREAM_DEPENDS_E

　　CURLOPT_STREAM_WEIGHT

　　Set this HTTP/2 stream‘s weight. See CURLOPT_STREAM_WEIGHT

4.　　调用curl_easy_perform（）函数完成传输任务

　　CURL_EXTERN CURLcode curl_easy_perform(CURL *curl);

5.　　调用curl_easy_cleanup（）释放内存

　　CURL_EXTERN void curl_easy_cleanup(CURL *curl);

实例：

#include <stdio.h>
#include <stdlib.h>
#include <curl\curl.h>

FILE *fp = NULL;
int UTF8ToGBK(char const * strUTF8) ;

size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream)
{
    //int written = fwrite(ptr, size, nmemb, (FILE *)fp);
	UTF8ToGBK((char *)ptr);  

    //return written;
	return 0;
}

int UTF8ToGBK(char const * strUTF8)
{
    int len = MultiByteToWideChar(CP_UTF8, 0, strUTF8, -1, NULL, 0);
    WCHAR* wszGBK = new WCHAR[len+1];
    memset(wszGBK, 0, len * 2 + 2);
    MultiByteToWideChar(CP_UTF8, 0, (LPCSTR)(LPCTSTR)strUTF8, -1, wszGBK, len);    

    len = WideCharToMultiByte(CP_ACP, 0, wszGBK, -1, NULL, 0, NULL, NULL);
    char *szGBK = new char[len + 1];
    memset(szGBK, 0, len + 1);
    WideCharToMultiByte(CP_ACP,0, wszGBK, -1, szGBK, len, NULL, NULL);
	char *p_temp = szGBK;
	int written = fwrite(p_temp, 1, strlen(p_temp), (FILE *)fp);

    delete[]szGBK;
    delete[]wszGBK;  

    return 0;
}  

int main(int argc, char *argv[])
{
	//定义CURL类型的指针
	CURL *p_curl = NULL;
	//定义CURLcode类型的变量，保存返回状态码
	CURLcode res;

	p_curl = curl_easy_init();
	if (NULL == p_curl)
	{
		printf ("curl_easy_init()  func  error\n");
		return -1;
	}

	if (NULL == (fp = fopen("baidu", "wb")))
	{
		curl_easy_cleanup(p_curl);
		return -1;
	}

	curl_global_init(CURL_GLOBAL_ALL);

	//设置curl选项. 其中CURLOPT_URL是让用户指定url. argv[1]中存放的命令行传进来的网址
    curl_easy_setopt(p_curl, CURLOPT_URL, "www.baidu.com");
	curl_easy_setopt(p_curl, CURLOPT_WRITEFUNCTION, write_data);
    //调用curl_easy_perform 执行我们的设置.并进行相关的操作. 在这里只在屏幕上显示出来.
    res = curl_easy_perform(p_curl);
    //清除curl操作.
     curl_easy_cleanup(p_curl);
	fclose(fp);

	return 0;
}

原文地址：https://www.cnblogs.com/Toney-01-22/p/9935026.html