n.打开文件
The fopen() function opens a file or URL. 函数的作用是：打开文件或URL。
Unfortunately that would not work because the fopen() call will fail if the remote file already exists. 如果远程文件已经存在则fopen()函数的操作将会失败。
Note: As of PHP 4.3.0, both source and dest may be URLs if the "fopen wrappers" have been enabled. 注:从PHP 4.
Opens for reading. If the file does not exist or cannot be found, the fopen call fails. 如果你不输入全路径，也可以，就默认在当前文件下！
Warning: fopen(): php_network_getaddresses: getaddrinfo failed: Temporary failure in name resolution in ...... 当然在服务器上手工访问那个地址是没有问题的，不是域名解析的问题。
As an example, the default implementation of streams is located in the file src/base/ftsystem.c and uses the ANSI fopen(), fseek(), and fread() calls. 举例来说，流的缺省实现位于文件src/base/ftsystem.
