Working with the Unix OS

C Libraries
}
if ((fp->flag&( _READ|_EOF|_ERR)) != _READ)
return EOF;
bufsize = (fp->flag & _UNBUF) ? 1: BUFSIZ;
if (fp->base == NULL) /* no buffer yet */
if ((fp->base = (char *) malloc(bufsize) == NULL)
return EOF; /* can't get buffer
fp->ptr = fp->base;
fp->cnt = read(fp->fd, fp->ptr, bufsize);
if (--fp->cnt < 0)
{
if (fp->cnt == -1)
fp->flag |= _EOF;
else
fp->flag |= _ERR;
fp->cnt = 0;
return EOF;
}
return (unsigned char) *fp->ptr++;
Initialization of array _iob:
FILE _iob[OPEN_MAX] = { /* stdin, stdout, stderr */
{ 0, (char *) 0, (char *) 0, _READ, 0 },
{ 0, (char *) 0, (char *) 0, _WRITE, 1 },
{ 0, (char *) 0, (char *) 0, _WRITE | _UNBUF, 2 },
};
Reading Directories
A directory is a list of filenames and an indication of where they are located. The inode for a file is where all
information about a file except its name is kept.
To show a list of files lets write a fsize program (1s), using three routines "opendir", "readdir" and "closedir" to
provide system independent access to the name and inode number in a directory entry.
/* dirent.h */
#define NAME_MAX 14 /* longest filename component */
typedef struct{ /* portable directory entry */
long ino; /* inode number */
char name[NAME_MAX+1); /* name + '\0' terminator */
}Dirent;
typedef struct{ /* minimal DIR: no buffering, etc */
int fd; /* file descriptor for directory */
Dirent d; /* the directory entry */
}DIR;
DIR *opendir(char *dirname);/* prototypes */
Dirent *readdir(DIR *dfd);
void closedir(DIR *dfd);
The system call "stat" takes a filename and returns all of the information in the inode for that file, or -1 for an error.
char *name;
struct stat stbuf;
int stat(char *, struct stat *);
stat(name, &stbuf);
Fills the structure "stbuf" with the inode information for the file name. This structure is described in
.
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