Quel est le processus de téléchargement de fichiers php ?

<form action="test.php" method="post" enctype="multipart/form-data">
  <input type="file" name="myfile">
  <input type="submit" value="上传">
</form>

<input type="hidden" name="MAX_FILE_SIZE" value="8096">
<input type="file" name="myfile" accept="image/jpeg,image/png">

<?php
  header(&#39;Content-type:text/html;charset=utf-8&#39;);
  $myfile=$_FILES[&#39;myfile&#39;];
  //获取文件数组[&#39;myfile&#39;]的属性tmp_name与name
  $tmp=$myfile[&#39;tmp_name&#39;];
  $picname=$myfile[&#39;name&#39;];
  //windows采用GBK编码，php采用utf-8编码，需要改变文件名的编码格式
  $picname=iconv(&#39;utf-8&#39;,&#39;GBK&#39;,$picname);
  //将零时文件$tmp移动到指定目录userpic并命名为$picname
  copy($tmp,"userpic/".$picname);

$error=$myfile['myfile']['error'];
  if ($error==0){//为0，代表上传成功
    if (move_uploaded_file($tmp,"userpic/".$picname)) {
      echo "移动文件成功";
    }else{
      echo "移动文件失败";
    }
  }else{//不为0，匹配错误信息
    switch ($error){
      case 1:
        echo "超过文件最大上传限制";//php.ini中upload_max_filesize
        break;
      case 2:
        echo "超过表单文件大小限制";//HTML表单中MAX_FILE_SIZE选项
        break;
      case 3:
        echo "文件部分被上传";
        break;
      case 4:
        echo "未选择上传文件";
        break;
      case 7://文件写入失败
      case 8:
        echo "系统错误";
        break;
    }
  }

<!--表单隐藏域对上传大小进行限制-->
<input type="hidden" name="MAX_FILE_SIZE" value="2097152">
<!--accept 对文件类型限制-->
<input type="file" name="myfile" accept="image/jpeg,image/png">

$size=$myfile['size'];//获取文件大小
$MaxSize=2097152;//设置最大允许字节
$type=$myfile['type'];//获取图片类型
$AllowTypr=array('image/jpeg','image/png','image/gif');//允许类型数组
if ($error==0){//为0，代表上传成功
  if ($size>$MaxSize){
    echo "<script>alert(&#39;文件大小超过限制&#39;);</script>";
    echo "<script>history.back(1);</script>";
    exit();
  }
  if (!in_array($type,$AllowTypr)){
    echo "<script>alert(&#39;请上传正确图片类型&#39;);</script>";
    echo "<script>history.back(1);</script>";
    exit();
  }