Detailed introduction to php file upload

First of all, let me state that this chapter contains a lot of content and is relatively difficult. You must have an attitude of fighting with yourself. Don’t miss the subtleties, practice more and more is the way to go.

Learning is like climbing a mountain. You have to do it step by step. First, set a small goal for yourself, and then persevere in climbing higher, and finally reach the top.

Please consider the above two pieces of advice carefully

1. Description of my preparations.

Editor: sublime text3 (Which editor you use depends on your preference)

Server construction: Use phpstudy2014 to build the server, server The file is stored in the www file on the D drive of my computer. (Installing phpstudy will automatically generate the www file, you decide which disk to install it on). Run phpstudy and enter localhost in the browser address bar to access files on the server.

The process of uploading files: The browser uploads the file on the client, click submit, the file is sent to a php file in the server for processing, and the php saves the uploaded file to server.

2. Create the form

Please see my html code


##enctype
In the Form element In the syntax, EncType indicates the format of the submitted data. The Enctype attribute specifies the encoding type used by the browser when sending data back to the server. There are three types of enctype:

1. application/x-www-form-urlencoded: Form data is encoded as name/value pairs. This is a standard encoding format.

2. multipart/form-data: Form data is encoded as a message, and each control on the page corresponds to a part of the message.

3. text/plain: The form data is encoded in plain text without any controls or formatting characters.

Supplement (just take a look): The enctype attribute of orm is the encoding method. There are two commonly used ones: application/x-www-form-urlencoded and multipart/form-data. The default is application/x- www-form-urlencoded. When the action is get, the browser uses the x-www-form-urlencoded encoding method to convert the form data into a string (name1=value1&name2=value2...), then appends the string to the end of the url, splits it with ?, and loads it. this new url. When the action is post, the browser encapsulates the form data into the http body and then sends it to the server. If there is no type=file control, just use the default application/x-www-form-urlencoded. But if there is type=file, multipart/form-data will be used. The browser will divide the entire form into control units, and add information such as Content-Disposition (form-data or file), Content-Type (default is text/plain), name (control name), and Add delimiter (boundary).

It’s a bit difficult to understand.

In short, remember two sentences: if there is type=file in the input tag, then enctype=multipart/form-data. If there is no type=file, application/x-www-form-urlencoded is generally used.

When uploading files, the data must undergo certain transformations before they can be uploaded to the server. The difference between application/x-www-form-urlencoded and multipart/form-data is the conversion encoding method.


3. Create a php file to process the uploaded files.


The effect after uploading the file is as follows:



Each uploaded file has name, type, size , tmp_name and other information. After the file is uploaded, the file-related information is stored in the FILES array variable. _FILES["myfile"]["name"] is equivalent to accessing a multi-dimensional array. FILES first obtains the file data uploaded by the input form named myfile, and then accesses name, type, size, error and other data. _FILES["myfile"]["error"] is used to handle situations where files are not uploaded normally, such as exceeding the uploaded file size limit. If FILES["myfile"]["error"]=0, it means the file is uploaded normally. _FILES["myfile"]["error"]>0 means the file was not uploaded normally.

FILES[“myfile”][“error”]=1 The uploaded file exceeds the server limit, such as exceeding the server space size. _FILES["myfile"]["error"]=2 exceeds the browser limit for uploading $_FILES["myfile"]["error"]=3 Only part of the file is uploaded

FILES["myfile" ]["error"]=4 No file was uploaded. _FILES["myfile"]["error"] can also be 5, 6, 7, or 8. I won't go into details here. Just know that when it is greater than 0, it means there is an error in uploading the file.


Upload restrictions
Normally, the server usually limits the size or type of files uploaded by the server. We add restrictions on the uploaded file code based on the above php code.

First familiarize yourself with the usage of several functions:

The explode() function is used to split a string. For example: explode(".","aaa.HTML") divides the string into two strings: "aaa" and "HTML" at the point position. These two characters Strings are stored sequentially in the same array.

end() gets the value of the last element in the array.

in_array() searches for an element in the array to see if it exists. It returns true if it exists and false if it does not exist.

<?php
//第一步：明确服务器规定上传至服务器的文件类型。这里我们只允许上传以下类型的图片。
$allowedExts = array("gif", "jpeg", "jpg", "png");// 允许上传的图片后缀
//第二部：获取上传的文件名称，通过explorde（）函数将其分割成字符串形式的数组。
$temp = explode(".", $_FILES["myfile"]["name"]);
echo $_FILES["file"]["size"];

$extension = end($temp);   // end函数用于获取数组中最后一个元素的值。
//第三步：列出上传文件需要满足的条件
if ((($_FILES["myfile"]["type"] == "image/gif")
|| ($_FILES["myfile"]["type"] == "image/jpeg")
|| ($_FILES[myfile"]["type"] == "image/jpg")
|| ($_FILES["myfile"]["type"] == "image/pjpeg")
|| ($_FILES["myfile"]["type"] == "image/x-png")
|| ($_FILES["myfile"]["type"] == "image/png"))
&& ($_FILES["myfile"]["size"] < 204800)  // 小于 200 kb
&& in_array($extension, $allowedExts))
  //in_array表示在$allowedExts数组中查找$extension这个字符串
{
  if ($_FILES["myfile"]["error"] > 0)
  {
    echo "错误：: " . $_FILES["myfile"]["error"] . "<br>";
    //举个例子服务器空间不足，文件只能上传部分就会出现错误。
  }
  else
  {
    echo "上传文件名: " . $_FILES["myfile"]["name"] . "<br>";
    echo "文件类型: " . $_FILES["myfile"]["type"] . "<br>";
    echo "文件大小: " . ($_FILES["myfile"]["size"] / 1024) . " kB<br>";
    echo "文件临时存储的位置: " . $_FILES["myfile"]["tmp_name"] . "<br>";
  }
}
else
{
  echo "非法的文件格式";
}
?>

4. Save the uploaded file

After the file is uploaded, it is saved in a temporary location. It will disappear when the script ends. If we want to save it permanently on the server, we need to save it in another location.

. file_exists(“upload/” . FILES[“file”][“name”]) checks whether the file or directory exists. .moveuploadedfile(_FILES["file"]["tmp_name"], "upload/" . $_FILES["myfile"]["name"]);Move the uploaded file from the temporary location to the server space.

<?php
//第一步：明确服务器规定上传至服务器的文件类型。这里我们只允许上传以下类型的图片。
$allowedExts = array("gif", "jpeg", "jpg", "png");// 允许上传的图片后缀
//第二部：获取上传的文件名称，通过explorde（）函数将其分割成字符串形式的数组。
$temp = explode(".", $_FILES["myfile"]["name"]);
echo $_FILES["myfilefile"]["size"];
$extension = end($temp);   // end函数用于获取数组中最后一个元素的值。
//第三步：列出上传文件需要满足的
if ((($_FILES["myfile"]["type"] == "image/gif")
|| ($_FILES["myfile"]["type"] == "image/jpeg")
|| ($_FILES["myfile"]["type"] == "image/jpg")
|| ($_FILES["myfile"]["type"] == "image/pjpeg")
|| ($_FILES["myfile"]["type"] == "image/x-png")
|| ($_FILES["myfile"]["type"] == "image/png"))
&& ($_FILES["myfile"]["size"] < 204800)  // 小于 200 kb
&& in_array($extension, $allowedExts))//in_array表示在$allowedExts数组中查找$extension这个字符串
{
  if ($_FILES["myfilefile"]["error"] > 0)
  {
    echo "错误：: " . $_FILES["myfile"]["error"] . "<br>";
  }
  else
  {
    echo "上传文件名: " . $_FILES["myfile"]["name"] . "<br>";
    echo "文件类型: " . $_FILES["myfile"]["type"] . "<br>";
    echo "文件大小: " . ($_FILES["myfile"]["size"] / 1024) . " kB<br>";
    echo "文件临时存储的位置: " . $_FILES["myfile"]["tmp_name"] . "<br>";

    // 判断当期目录(即www文件夹中)下的 upload 目录（自己创建，名字自取）是否存在该文件
    // 如果没有 upload 目录，你需要创建它，upload 目录权限为 777
    if (file_exists("upload/" . $_FILES["myfile"]["name"]))
    {
      echo $_FILES["myfile"]["name"] . " 文件已经存在。 ";
    }
    else
    {
      // 如果 upload 目录不存在该文件则将文件上传到 upload 目录下
      move_uploaded_file($_FILES["myfile"]["tmp_name"], "upload/" . $_FILES["file"]["name"]);//
      echo "文件存储在: " . "upload/" . $_FILES["myfile"]["name"];
    }
  }
}
else
{
  echo "非法的文件格式";
}
?>

The above is the detailed introduction to PHP file upload. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!