留心一下fopen打开文件的模式

函数原型：

FILE *fopen(const char *path, const char *mode);

打开模式详解：

       r      Open  text  file  for  reading.  The stream is positioned at the

              beginning of the file.

       r+     Open for reading and writing.  The stream is positioned  at  the

              beginning of the file.

       w      Truncate  file  to  zero length or create text file for writing.

              The stream is positioned at the beginning of the file.

       w+     Open for reading and writing.  The file is created  if  it  does

              not  exist, otherwise it is truncated.  The stream is positioned

              at the beginning of the file.

       a      Open for appending (writing at end of file).  The file  is  cre-

              ated  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.

 

需要注意如下的两点（个人在前段时间遇到的）：

(1) "r" 与 "r+"的区别；后者打开的文件具有写权限

(2) "rw"  与 "wr"的区别；在fopen一个当前不存在的文件时，前者会core掉