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HomeBackend DevelopmentPHP Tutorialphp实现图片上传并进行替换操作_PHP

首先建立两个文件: change.html 和 change.php

change.html 文件的表单代码如下:

<html>
<head>
<title>change file example.</title>
<meta charset="UTF-8">
</head>
<body>
<form method="post" action="changefile.php" enctype="multipart/form-data">
<table border=0 cellspacing=0 cellpadding=0 align=center width="100%">
<tr>
<td width=55 height=20 align="center">
<input type="hidden" name="MAX_FILE_SIZE" value="2000000" />
文件:
</td>
<td>
<input name="file" type="file" />
<input type="submit" name="submit" value="submit" /> 
</td>
</tr>
</table>
</form>
</body>
</html>

这里有几个要注意的地方,首先看这句

这里我们采用POST方法,个别浏览器还支持PUT方法,当然这需要对脚本进行修改,我并不建议这么做。表单中必须设置enctype="multipart/form-data,这样,服务器就知道上传文件带有常规表单信息,记住,这个是必须设置的。此外还需要一个隐藏域来限制上传文件的最大长度这里name必须设置成MAX_FILE_SIZE,其值就是上传文件的最大长度,单位是B,这里我限制成2M。再看这句type="file"说明了文件类型,这样一个基本的上传文件接口就完成了,接下来讲讲如何用PHP来处理上传的文件,此外你的php.ini中设置的上传文件最大长度可能会影响到你的实际上传,请根据实际情况修改,另PHP的上传是先传到临时目录,在移至指定目录的,了;临时目录的可根据需要修改,也可使用默认值……

以下为表单提交change.php文件代码,来看看这个文件都有什么:

<&#63;php
header("content-type:text/html;charset=utf-8");

 

/**
* @param string $oldfile 需要更换的文件名(包含具体路径名)
*/
function changeFile($oldfile){
$newfile = $_FILES['file']['name'];//获取上传文件名
$fileclass = substr(strrchr($newfile, '.'), 1);//获取上传文件扩展名,做判断用
$type = array("jpg", "gif", "bmp", "jpeg", "png");//设置允许上传文件的类型
if(in_array(strtolower($fileclass), $type)){
if(file_exists($oldfile)){
unlink($oldfile);
}

if(is_uploaded_file($_FILES['file']['tmp_name'])){//必须通过 PHP 的 HTTP POST 上传机制所上传的 
if(move_uploaded_file($_FILES['file']['tmp_name'], $oldfile)){ 
//输出图片预览
echo "<center>您的文件已经上传完毕 上传图片预览: </center><br><center><img  src='$oldfile' alt="php实现图片上传并进行替换操作_PHP" ></center>";
}
}else{
echo "<center>上传失败,文件大于2M,请重新上传!</center>";
}
}else{
$text = implode(",", $type);
echo "<center>您只能上传以下类型文件:", $text, "</center><br>";
// echo "<script>alert('您只能上传以下类型文件:$text')</script>";
}
}

changeFile("./files/1.png");

刚看这些你可能有点晕~~,慢慢看,你就会发现其实这玩意SO EASY!!先讲下原理,该程序以上传图片为例,先判断文件类型是否为图片格式,若是则上传文件,接着上传文件到并替换指定文件,成功上传则输出上传的图片预览。这里要对程序中一些函数作些解释。先看substr(strrchr($newfile, '.'), 1), strrchar()函数有什么作用呢,我举个例子大家就知道,比如一个图片文件 pic.jpg,我们用 strrchar()处理,strrchr(pic.jpg,'.'),它将返回.jpg,明白了吗?该函数返回指定字符在该字符串最后出现的位置后的字符串。配合 substr() 我们就可以取到jpg,这样我们就得到了文件的后缀名,来判断上传文件是否符合指定格式。本程序把指定的格式放在一个数组中,实际使用时可根据需要添加。
接着,我们调用判断文件类型的函数,并将其转化为小写strtolower($_FILES['file']['name']),这里有个很关键的东东$_FILES ,这是个超级全局数组,保存了需要处理的表单数据,如果开启了register_globals,也可以直接访问,但这是不安全的。看刚才那个上传接口name="file" type="file">,根据这个表单名称,我们可以得到很多信息:
$_FILES['file']['name']--   得到文件名称
$_FILES['file']['tmp_name']--得到临时存储位置
$_FILES['file']['size']--得到文件大小
$_FILES['file']['type']--得到文件MIME类型
得到这些信息,就可以轻松判断文件的信息了,是不是很方便?^_^,接下来还有一些函数需要了解,file_exists()--判断指定目录是否存在,不存在我们当然不能上传(好像是废话!),is_uploaded_file--判断文件是否已经通过HTTP POST上传,move_uploaded_file--将上传文件移至指定目录。成功上传,我们就输出预览,否则输出上传失败……

内容很详细,过程也记录下来供大家仔细研究,希望对大家的学习有所帮助。

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