php利用GD库生成缩略图示例

代码如下：

<form method="post" action="suo_do.php" enctype="multipart/form-data"> 
<input type="file" name="pic" /> 
<input type="submit" value="上传1" /> 
</form> 
<?php 
header("content-type:text/html;charset=gbk"); 
ini_set("date.timezone","Asia/chong"); 
//判断文件是否为空 
if(empty($_FILES)){ 
echo"上传文件过大"; 
exit; 
} 
//判断文件上传是否有错误 
if($_FILES['pic']['error']){ 
echo "上传文件"; 
exit; 
} 
//判断文件类型是否非法获取文件后缀 
$allowtype=array("jpg","png","jpeg","gif"); 
$a=explode('.',$_FILES['pic']['name']); 
$index=count($a)-1; 
$ex=strtolower($a[$index]); 
if(!in_array($ex,$allowtype)){ 
echo "上传文件非法"; 
exit; 
} 
$file=date('YmdHis').rand().".".$ex; 
$src=$_FILES['pic']['tmp_name']; 
$des="upload/".$file; 
$rs=move_uploaded_file($src,$des); 


//缩略图 
//读取已经上传图片 
$image=imagecreatefromjpeg($des); 
$a=getimagesize($des); 
$w=$a[0]; 
$h=$a[1]; 
if($w>$h){ 
$width=300; 
$height=$width/$w*$h; 
}else if($w<$h){ 
$height=300; 
$width=$height/$h*$w; 
}else{ 
$width=300; 
$height=300; 
} 
//创建空白新图片 
$newimage=imagecreatetruecolor($width, $height); 
//copy源图片内容 copy新图片 
imagecopyresized($newimage, $image, 0,0, 0,0, $width, $height, $w, $h); 
$filename="upload/s_".$file; 
imagejpeg($newimage,$filename);