Warning: session_start() [function.session-start]: Cannot se
在很多时间使用了session就会出来如下提示了，
Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/u114264/include/db_mysql教程.class.php教程:1) in /home/u114264/login1.php on line 3
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/u114264/include/db_mysql.class.php:1) in /home/u114264/login1.php on line 3
分析最大的可能是在session_start()前面有字符输出包括空格 ，只要处理就好了，
还有一种方法直接给session_start()加上@session_start()就没事了。不推荐
地址解决方案。
最通常的解决方案。打开output_buffering = 4096; 全局性质。
第二种解决方案。
ob_start ：打开输出缓冲区
函数格式：void ob_start(void)
说明：当缓冲区激活时，所有来自PHP程序的非文件头信息均不会发送，而是保存在内部缓冲区。为了输出缓冲区的内容，可以使用ob_end_flush()或flush()输出缓冲区的内容。
注意的地方：
如果使用utf-8编码，一定要去掉UTF-8中的BOM，这都是因为utf-8编码文件含有的bom原因，而php4,5都是不支持bom的。去掉bom，可以用Notepad++打开转换一下。
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