Analysis of commonly used file upload functions in PHP

With the development of Web applications, file upload has become one of the common functions in Web program development. As a powerful server-side programming language, PHP also provides a series of functions for processing file uploads. The following will analyze the commonly used file upload functions in PHP.

1. move_uploaded_file()

move_uploaded_file() is one of the most commonly used file upload functions in PHP. Its function is to move the uploaded file from the temporary directory to the specified Table of contents. Its syntax is as follows:

move_uploaded_file (string $filename, string $destination): bool

Among them, $filename is the source file path, $destination is the destination file path, and returns a bool type value Indicates whether the move was successful.

Example:

$filename=$_FILES['file']['tmp_name'];
$destination="upload/".$_FILES['file']['name'];
if(move_uploaded_file($filename,$destination)){
    echo "上传成功";
}else{
    echo "上传失败";
}

2. is_uploaded_file()

The is_uploaded_file() function is used to determine whether the specified file is uploaded through HTTP POST. If so, this function returns true, otherwise it returns false. The syntax of this function is as follows:

is_uploaded_file (string $filename) : bool

Among them, $filename represents the file name to be tested, and the return value is of bool type.

Example:

if(is_uploaded_file($_FILES['file']['tmp_name'])){
    echo "这是上传的文件";
}else{
    echo "这不是上传的文件";
}

3. $_FILES

$_FILES is a global variable in PHP used to obtain uploaded file information. It is a two-dimensional array . For each file uploaded, the $_FILES array contains 5 elements:

• $_FILES['name']: the name of the uploaded file;
• $_FILES['type ']: Type of uploaded file;
• $_FILES['size']: Size of uploaded file;
• $_FILES['tmp_name']: Temporary file name of uploaded file;
• $_FILES['error']: Error code when uploading files.

Example:

echo "上传文件名：".$_FILES['file']['name']."<br>";
echo "上传文件类型：".$_FILES['file']['type']."<br>";
echo "上传文件大小：".$_FILES['file']['size']."<br>";
echo "上传文件的临时文件名：".$_FILES['file']['tmp_name']."<br>";
echo "上传文件的错误代码：".$_FILES['file']['error']."<br>";

4. move_uploaded_file() and copy()

Both the move_uploaded_file() and copy() functions can realize the file transfer Copy from one place to another but the difference between them is the security of uploading files. When the move_uploaded_file() function saves the file, it will check whether the uploaded file was uploaded through HTTP POST, and the temporary file will be automatically deleted. The copy() function simply copies the file without performing such checks, so the security is relatively low. Therefore, when processing file uploads, you should try to use the move_uploaded_file() function.

In summary, for PHP file upload processing, it is recommended to use the move_uploaded_file() function to process uploaded files, and use the is_uploaded_file() function and the $_FILES global variable for verification and file information acquisition. This ensures the security and reliability of uploaded files.

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