解决了什么问题：curl在使用各种方式上传文件到服务器。
一般的文件上传是通过html表单进行的，通过CURL可以不经过浏览器，直接在服务器端模拟进行表单提交，完成POST数据、文件上传等功能。

服务器端PHP代码：

<?php
if ((( $_FILES["file"]["type"] == "image/gif") || ( $_FILES["file"]["type"] == "image/jpeg") || ( $_FILES["file"]["type"] == "image/pjpeg")) && ( $_FILES["file"]["size"] < 200000)) {
     if ( $_FILES["file"]["error"] > 0) {
         echo "Return Code: " .  $_FILES["file"]["error"] . "<br />";
    }  else {
         if ( file_exists("upload/" .  $_FILES["file"]["name"])) {
             echo  $_FILES["file"]["name"] . " already exists. ";
        }  else {
             move_uploaded_file( $_FILES["file"]["tmp_name"], "data/" .  $_FILES["file"]["name"]);
             //  echo "Stored in: " . "data/" . $_FILES["file"]["name"];
             echo "文件上传成功!";
        }
    }
}  else {
     echo " 文件无效!";
}
?>

客户端提交的form:

< form  action ="upload.php"  method ="post"  enctype ="multipart/form-data" >
                         < input  type ="file"  name ="file" />
                         < input  type ="submit"  class ="btn btn-primary btn-large"  value ="上传文件"   />
   </ form >


在控制台使用curl上传的例子：

curl -F "action=upload.php" -F "method=post" -F "file=@/Users/mark/xx.gif" http: // ylg.zs108.com:8080/tmp/upload.php


使用libcurl实现的代码：
#include <stdio.h>
#include <stdlib.h>
#include < string.h>
#include <curl/curl.h>

#define POSTURL "http: // ylg.zs108.com:8080/tmp/upload.php"
#define POSTFIELDS "?action=upload&method=post"
#define FILENAME "curlposttest.log"

size_t write_data( void *buffer, size_t size, size_t nmemb,  void *userp);

int main( int argc,  char *argv[]) {
    CURL *curl;
    CURLcode res;
    FILE *fptr;
     struct curl_slist *http_header = NULL;
    
     if ((fptr = fopen(FILENAME, "w")) == NULL) {
        fprintf(stderr, "fopen file error: %s\n", FILENAME);
        exit(1);
    }
    
    curl = curl_easy_init();
    
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, fptr);
    
     struct curl_httppost *formpost = 0;
     struct curl_httppost *lastptr  = 0;
    curl_formadd(&formpost, &lastptr, CURLFORM_PTRNAME, "reqformat", CURLFORM_PTRCONTENTS, "plain", CURLFORM_END);
    curl_formadd(&formpost, &lastptr, CURLFORM_PTRNAME, "file", CURLFORM_FILE, "/Users/hanyanyan/xx.gif", CURLFORM_END);
    curl_easy_setopt(curl, CURLOPT_URL, POSTURL);
    curl_easy_setopt(curl, CURLOPT_HTTPPOST, formpost);
    
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
}

size_t write_data( void *buffer, size_t size, size_t nmemb,  void *userp) {
    FILE *fptr = (FILE*)userp;
    fwrite(buffer, size, nmemb, fptr);
}  

编译方式：gcc -o curl_post_file filename.c -lcurl

后期调整：
<! DOCTYPE html >
<!--  saved from url=(0044)http://ylg.zs108.com:8080/dp/uploadtest.html  -->
< html  lang ="en" >< head >< meta  http-equiv ="Content-Type"  content ="text/html; charset=UTF-8" >
         < meta  charset ="UTF-8" >
         < title >Document </ title >
     < style  type ="text/css" ></ style ></ head >
     < body >
         < div  class ="containter-fluid" >
             < div  class ="row-fluid" >
                 < div  class ="span8 offset2" >
                    
                     < form  action ="http://ylg.zs108.com:8080/dp/upload.php"  method ="post"  enctype ="multipart/form-data" >
                         < table  cellpadding ="10"  border ="1" >
                             < tbody >< tr >
                                 < td >wid </ td >
                                 < td >< input  type ="text"  name ="wid"  value ="dengpan" ></ td >
                             </ tr >
                             < tr >
                                 < td >text </ td >
                                 < td >< input  type ="text"  name ="text"  value ="哈哈哈呵呵" ></ td >
                             </ tr >
                             < tr >
                                 < td >stime </ td >
                                 < td >< input  type ="text"  name ="stime"  value ="13" ></ td >
                             </ tr >
                             < tr >
                                 < td >ssize </ td >
                                 < td >< input  type ="text"  name ="ssize"  value ="15" ></ td >
                             </ tr >
                             < tr >
                                 < td >lid </ td >
                                 < td >< input  type ="text"  name ="lid"  value ="2" ></ td >
                             </ tr >
                             < tr >
                                 < td >type </ td >
                                 < td >< input  type ="text"  name ="type"  value ="2" ></ td >
                             </ tr >
                             < tr >
                                 < td >sound </ td >
                                 < td >< input  type ="file"  name ="sound" ></ td >
                             </ tr >
                             < tr >
                                 < td ></ td >
                                 < td >< input  type ="submit"  value ="提交" ></ td >
                             </ tr >
                         </ tbody ></ table >
                     </ form >
                 </ div >
             </ div >
         </ div >
    

</ body ></ html >

命令行：
curl －F  " method=post " -F  " action=upload.php " -F  " wid=dengpan " -F  " text=hh " -F  " stime=13 " -F  " ssize=15 " -F  " lid=2 " -F  " type=2 " -F  " sound=@/Users/hanyanyan/million.amr " http://ylg.zs108.com: 8080/dp/upload.php
返回代码：
{ " code " : 1 , " result " :{ " sound " : " http:\/\/ylg.zs108.com:8080\/dp\/data\/sounds\/1378815106-a3864fc57553bf4b299b4d4c0ce07649.amr " }}
最后在贴一段PHP上传的代码吧
需要被上传的文件需要在文件名前加上“@”以示区分，并且，文件名需要是完整路径。
 以下php函数来模拟html表单的提交数据：
function uploadByCURL( $post_data, $post_url){
     $curl = curl_init();
    curl_setopt( $curl, CURLOPT_URL,  $post_url);
    curl_setopt( $curl, CURLOPT_POST, 1 );
    curl_setopt( $curl, CURLOPT_POSTFIELDS,  $post_data);
    curl_setopt( $curl, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt( $curl,CURLOPT_USERAGENT,"Mozilla/4.0");
     $result = curl_exec( $curl);
     $error = curl_error( $curl);
     return  $error ?  $error :  $result;
}

/* 函数的使用： */

$url = "http://127.0.0.1/app.php";
$data =  array(
    "username" =>  $username,
    "password"  =>  $password,
    "file1"  => "@". realpath("photo1.jpg"),
    "file2"  => "@". realpath("file2.xml")
);
print_r(uploadByCURL( $data, $url));