输入输出函数记录

/*
实现readline，如果要指定文件，就用fgets()实现，如果从串口读，用哪个都行了。
char * readline (const char *prompt);

#include <stdio.h>
int fgetc(FILE *stream);
char *fgets(char *s, int size, FILE *stream);
int getc(FILE *stream);
int getchar(void);
char *gets(char *s)

fgets()  reads  in at most one less than size characters from stream and stores them into
       the buffer pointed to by s.  Reading stops after an EOF or a newline.  If  a  newline  is
       read,  it  is stored into the buffer.  A terminating null byte ('\0') is stored after the
       last character in the buffer.
       fgets() return s on success, and NULL on error or  when  end  of  file  occurs
       while no characters have been read.

fgetc()  reads  the next character from stream and returns it as an unsigned char cast to
       an int, or EOF on end of file or error.

getc() is equivalent to fgetc() except that it may be implemented as a macro which evalu‐
       ates stream more than once.

getchar() is equivalent to getc(stdin).

gets() reads a line from stdin into the buffer pointed to by s until either a terminating
       newline or EOF, which it replaces with a null byte ('\0').  No check for  buffer  overrun
       is performed (see BUGS below).
       gets() return s on success, and NULL on error or  when  end  of  file  occurs
       while no characters have been read.
       Never  use  gets().  Because it is impossible to tell without knowing the data in advance
       how many characters gets() will read, and because gets() will continue to  store  charac‐
       ters  past  the end of the buffer, it is extremely dangerous to use.  It has been used to
       break computer security.  Use fgets() instead.

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ferror系列、fdopen、sscanf/sprintf系列。
*/