Uploading and downloading files in php

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File upload and download
Upload
Client to server
Client settings (form settings)

1. The form submission method must be post
2. Add enctype="multipart/form-data"
enctype on the form: specifies how to encode the form data before sending the data to the server.
multipart/form-data: Do not encode characters. It can be understood that data is transmitted in the form of data stream (binary).
application/x-www-form-urlencode: Default option, encode all characters before sending
3,
1. It can be used or not. This is a suggestion of PHP. Some browsers do not support it at all.
2. Let the user make a pre-judgment before the browser sends the file. If the file size is larger than the set bytes, the actual post work cannot be performed and the content will not be sent to the server.
3. To be placed above
Server-side settings
1. file_uploads = On Whether to allow uploading
2. upload_max_filesize = 2M The maximum upload file size allowed by PHP
3. post_max_size = 8M Limit the size of data that can be received through the post method .
post_max_size must be greater than upload_max_filesize
4. upload_tmp_dir = "C:\xampp\tmp" The temporary directory after uploading files.
php script receives uploaded data
1. Use $_FILES to receive the uploaded data.
2. The meaning of each element in $_FILES
name=>Uploaded file name
type=> The mime type is used to set a way for files with a certain extension to be opened by an application. When the file with the extension is accessed, the browser will automatically specify the application to open.
tmp_name=>The name of the temporary file during upload. After the file upload is completed, the generated temporary file will be stored in the temporary file directory by default. As long as you copy the contents of this temporary file, the upload is actually successful. This file will be deleted regardless of whether the copy is successful or not.
error=>Upload error number
              The value is 0, no error occurred, the file was uploaded successfully
                                                                              The value is 0 1. The uploaded file exceeds the value limited by the upload_max_filesize option in php.ini. The value of
is 2, and the size of the upload file exceeds the value specified by the Max_file_size option in the html form.
This is the value of 3, and only part of the file is uploaded.
This is the value of 4, and no files are uploaded.
The value is 6 and the temporary folder cannot be found. Introduced in PHP 4.3.10 and PHP 5.0.3.
                                                                                                                                                      ’ ’                               ’ ’ ’ ’ it ’ s to be 7 means that the file writing failed.
size=>The size of the file is in bytes.
3. Move the uploaded temporary file to the specified directory
move_uploaded_file();
Note: If you upload For Chinese names, you must pay attention to character set issues. By default, the value you get is utf-8, but the default value of the XP system is GBK character set, so you need to convert
Be careful when uploading multiple files
Note that unlike other languages, the continue statement on switch has a similar effect to break. If you have a switch within a loop and want to continue to the next iteration in the outer loop, use continue 2.
Download
Server to client
Downloading with the help of http: If the browser can recognize the file, it will be parsed directly , if it cannot be recognized, it will provide download
Server settings
Directly tell the browser that this is a download file and do not parse it
1. header('content-type:text/html;charset=utf-8');//Set the character set
2. header('content-disposition:attachment');/ /Tell it to be a download file (attachment)
3. header('content-disposition:attachment;filename=xxxxx');//Tell it to be an attachment and give the file name (yes Added on the basis of point 2)
4. Read all the file contents, otherwise there will be no content
5. Tell the browser this How big is the file? header('content-length: file size'); Implement file upload and download

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