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php使用function_exists判断函数可用的方法_PHP

May 31, 2016 pm 07:27 PM
php function judgment

本文实例讲述了php使用function_exists判断函数可用的方法。分享给大家供大家参考。具体如下:

本文所述的函数用来建立一张 gif 格式图形,参数 im 为使用 imagecreate() 所建立的图片代码,参数 filename 可省略,若无本参数 filename,则会将图片直接送到浏览器端,记得在送出图片之前要先送出使用 content-type: image/gif 的标头字符串 (header) 到浏览器端,以顺利传输图片。若要使用透明背景的 gif 图,也就是 gif89a 的格式,需要先使用 imagecolortransparent() 配置透明背景.

代码如下:

$values=array(
  40,50,         //第一个顶点的坐标
  20,240,         //第一个顶点的坐标
  60,60,         //第一个顶点的坐标
  240,20,         //第一个顶点的坐标
  50,40,         //第一个顶点的坐标
  10,10         //第一个顶点的坐标
);
$im=imagecreatetruecolor(250,250);   //创建图像
$bg=imagecolorallocate($im,200,200,200);  //定义灰色背景
$yellow=imagecolorallocate($im,255,255,0);  //定义黄色前景
imagefilledpolygon($im,$values,6,$yellow);  //画出多边形
header('content-type: image/png');
//判断gif函数是否存在
if(function_exists("imagegif"))
{
  //如果存在,以gif格式输出
  header("content-type: image/gif");
  imagegif($im);
}
//判断jpeg函数是否存在
elseif(function_exists("imagejpeg"))
{
  //如果存在,以jpg格式输出
  header("content-type: image/jpeg");
  imagejpeg($im, "", 0.5);
}
//判断png函数是否存在
elseif (function_exists("imagepng"))
{
  //如果存在,以png格式输出
  header("content-type: image/png");
  imagepng($im);
}
//判断wbmp函数是否存在
elseif (function_exists("imagewbmp"))
{
  //如果存在,以bmp格式输出
  header("content-type: image/vnd.wap.wbmp");


header() 函数向客户端发送原始的 http 报头,认识到一点很重要,即必须在任何实际的输出被发送之前调用 header() 函数(在 php 4 以及更高的版本中,您可以使用输出缓存来解决此问题):

代码如下:

  imagewbmp($im);
}
else
{
  //如果都不支持,输出内容
  die("no image support in this php server");
}

该代码判断多种图像支持,然后用相应的格式输出图像.

语法:int imagegif(int im, string [filename]);

返回值:整数,函数种类:图形处理

希望本文所述对大家的PHP程序设计有所帮助。

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