一：

    1_3:  (1) DIR *opendir(const char *name);

         (2) DIR *fdopendir(int fd);

        On error, NULL is returned;

         (3) struct dirent *readdir( DIR *dp)

        On error, NULL is returned;

        (4) int closedir(DIR *dp);

         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>

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