文件上传与下载

文件操作是 PHP 中常见的操作之一，其中文件上传与下载也是常用的功能之一。下面我们就来详细介绍如何在 PHP 中实现文件上传与下载功能。

文件上传

1. 创建上传文件的表单

<form action="upload.php" method="post" enctype="multipart/form-data">
    Select File to upload:
    <input type="file" name="fileToUpload" id="fileToUpload">
    <input type="submit" value="Upload File" name="submit">
</form>

2. 创建处理文件上传的 PHP 脚本

<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($target_file,PATHINFO_EXTENSION));

// Check if file already exists
if (file_exists($target_file)) {
    echo "Sorry, file already exists.";
    $uploadOk = 0;
}

// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
}

// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
    echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
    $uploadOk = 0;
}

// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
    echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
    if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
        echo "The file ". htmlspecialchars( basename( $_FILES["fileToUpload"]["name"])). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}
?>

文件下载

1. 创建下载链接

<a href="download.php?file=example.txt">Download example.txt</a>

2. 创建处理文件下载的 PHP 脚本

<?php
$filename = $_GET['file'];
$filepath = 'downloads/' . $filename;

if (file_exists($filepath)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename="'.basename($filepath).'"');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($filepath));
    readfile($filepath);
    exit;
} else {
    echo 'File not found.';
}
?>

以上就是文件上传与下载的基本操作步骤，你可以根据实际需求进行修改和扩展。希望对你有帮助。