Warning: Cannot modify header information - headers already sent by (output started at file_path:line)

 "Warning: Cannot modify header information - headers already sent by (output started at file_path:line)"

• 原因：尝试修改HTTP头信息，但已有内容输出。
• 解决方法：确保在任何输出前设置HTTP头信息，检查是否有空白字符或注释提前输出。