一：
1_3: (1) DIR *opendir(const char *name); <dirent.h>
(2) DIR *fdopendir(int fd);
On error, NULL is returned;
(3) struct dirent *readdir( DIR *dp) <dirent.h>
On error, NULL is returned;
(4) int closedir(DIR *dp); <dirent.h>
0 on success, -1 on error.
1_4: (1) ssize_t read(int fd, void *buf, size_t count);
On success, return the number of bytes read, maybe smaller than count, and the file position is advanced by the number.
On error, -1 returned.
(2) ssize_t write(int fd, void *buf, size_t count);
On success, return the number of bytes writetten, maybe bigger than count.
1_5: (1) int getc(FILE *stream); <stdio.h>
On success, return the charactor read as an unsigned char cast to an int, or EOF end of file.
(2) int putc(int c, FILE *stream) <stdio.h>
On success, return the haractor read as an unsigned char cast to an int.
On error, return EOF.
1_6: (1) pid_t getpid(void); <unistd.h>
return the process ID of the calling process.
pid_t getppid(void);
return the process ID of the parent of the calling process.
1_7: (1) char *fgets(char *s, int size, FILE *stream);
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.
On success, return s.
Return NULL, on error or shen EOF occurs while no charactor have been read.