fopen的a+和rewind

记得以前出现过一次类似问题：

　

这次check_list代码就顺便修改一下。

　　来看看man fopen的结果；

 a      Open for appending (writing at end of file).  The file is created if it does not exist.  The stream is positioned at the end of the file.

 a+     Open for reading and appending (writing at end of file).  The file is created if it does not exist.  The initial file position
　　　　　　 for reading is at the beginning of the file, but output is always appended to the end of the file.

　即：无论用fseek，rewind等文件位置指针定位函数，在写入文件信息时，均只能写入到文件末尾

"a" = append: Open file for output at the end of a file. Output operations always write data at the end of the file, 
expanding it. Repositioning operations (fseek, fsetpos, rewind) are ignored. The file is created if it does not exist.

可以阅读man 相关文档。man 3 fopen

所以对于process的log 文件，检测文件不存在，这w+方式打开，如果存在则r+方式打开，如此可以使用rewind 调整文件偏移指针写入