php文件扩展名判断及获取文件扩展名的N种方法，
php文件扩展名判断及获取文件扩展名的N种方法，
下面代码是php文件扩展名判断
<!DOCTYPE>
<html>
<head>
<meta http-equiv="Content-type" content="text/html" charset="utf-8">
<title>check file</title>
</head>
<body>
<b>文件扩展名验证</b>
<input type="text" name="int" value="文件.php" onblur="check(this)" id="int">
<input type="button" value="检测" onclick="check_value()">
<script>
function check(obj){
if(obj.value == "" || obj.value.length<3){
alert("输入的长度不能小于3且不能为空!");
obj.focus();
}
}
function check_value(){
var str = $("int").value;
var repx = /\.(php|asp|jsp)$/i;
var type = str.substring(str.lastIndexOf("."),str.length);
if(type.match(repx) && str.lastIndexOf(".") != -1){
alert("文件扩展名正确");
$("int").focus();
}else{
alert("文件扩展名有误");
$("int").focus();
}
}
function $(obj){
return document.getElementById(obj);
}
</script>
</body>
</html>PHP中获取文件扩展名的N种方法
基本上就以下这几种方式：
第1种方法：
function get_extension($file)
{
substr(strrchr($file, '.'), 1);
}第2种方法：
function get_extension($file)
{
return substr($file, strrpos($file, '.')+1);
}第3种方法：
function get_extension($file)
{
return end(explode('.', $file));
}第4种方法：
function get_extension($file)
{
$info = pathinfo($file);
return $info['extension'];
}第5种方法：
function get_extension($file)
{
return pathinfo($file, PATHINFO_EXTENSION);
}以上几种方式粗看了一下，好像都行，特别是1、2种方法，在我不知道pathinfo有第二个参数之前也一直在用。但是仔细考虑一下，前四种方法都有各种各样的毛病。要想完全正确获取文件的扩展名，必须要能处理以下三种特殊情况。
没有文件扩展名
路径中包含了字符.，如/home/test.d/test.txt
路径中包含了字符.，但文件没有扩展名。如/home/test.d/test
很明显：1、2不能处理第三种情况，3不能正确处理第一三种情况。4可以正确处理，但是在不存在扩展名时，会发出一个警告。只有第5种方法才是最正确的方法。顺便看一下pathinfo方法。官网上介绍如下：
$file_path = pathinfo('/www/htdocs/your_image.jpg');
echo "$file_path ['dirname']\n";
echo "$file_path ['basename']\n";
echo "$file_path ['extension']\n";
echo "$file_path ['filename']\n"; // only in PHP 5.2+它会返回一个数组，包含最多四个元素，但是并不会一直有四个，比如在没有扩展名的情况下，就不会有extension元素存在，所以第4种方法才会发现警告。但是phpinfo还支持第二个参数。可以传递一个常量，指定返回某一部分的数据：
PATHINFO_DIRNAME - 目录
PATHINFO_BASENAME - 文件名（含扩展名）
PATHINFO_EXTENSION - 扩展名
PATHINFO_FILENAME - 文件名（不含扩展名，PHP>5.2）
这四个常量的值分别是1、2、4、8，刚开始我还以为可以通过或运算指定多个：
pathinfo($file, PATHINFO_EXTENSION | PATHINFO_FILENAME);
后来发现这样不行，这只会返回几个进行或运算常量中最小的那个。也就是四个标志位中最小位为1的常量。
以上内内容给大家介绍了php文件扩展名判断及获取文件扩展名的N种方法，希望大家喜欢。
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