buf.c

#include "apue.h"

void	pr_stdio(const char *, FILE *);
int		is_unbuffered(FILE *);
int		is_linebuffered(FILE *);
int		buffer_size(FILE *);

int
main(void)
{
	FILE	*fp;

	fputs("enter any character\n", stdout);
	if (getchar() == EOF)
		err_sys("getchar error");
	fputs("one line to standard error\n", stderr);

	pr_stdio("stdin",  stdin);
	pr_stdio("stdout", stdout);
	pr_stdio("stderr", stderr);

	if ((fp = fopen("/etc/passwd", "r")) == NULL)
		err_sys("fopen error");
	if (getc(fp) == EOF)
		err_sys("getc error");
	pr_stdio("/etc/passwd", fp);
	exit(0);
}

void
pr_stdio(const char *name, FILE *fp)
{
	printf("stream = %s, ", name);
	if (is_unbuffered(fp))
		printf("unbuffered");
	else if (is_linebuffered(fp))
		printf("line buffered");
	else /* if neither of above */
		printf("fully buffered");
	printf(", buffer size = %d\n", buffer_size(fp));
}

/*
 * The following is nonportable.
 */

#if defined(_IO_UNBUFFERED)

int
is_unbuffered(FILE *fp)
{
	return(fp->_flags & _IO_UNBUFFERED);
}

int
is_linebuffered(FILE *fp)
{
	return(fp->_flags & _IO_LINE_BUF);
}

int
buffer_size(FILE *fp)
{
	return(fp->_IO_buf_end - fp->_IO_buf_base);
}

#elif defined(__SNBF)

int
is_unbuffered(FILE *fp)
{
	return(fp->_flags & __SNBF);
}

int
is_linebuffered(FILE *fp)
{
	return(fp->_flags & __SLBF);
}

int
buffer_size(FILE *fp)
{
	return(fp->_bf._size);
}

#elif defined(_IONBF)

#ifdef _LP64
#define _flag __pad[4]
#define _ptr __pad[1]
#define _base __pad[2]
#endif

int
is_unbuffered(FILE *fp)
{
	return(fp->_flag & _IONBF);
}

int
is_linebuffered(FILE *fp)
{
	return(fp->_flag & _IOLBF);
}

int
buffer_size(FILE *fp)
{
#ifdef _LP64
	return(fp->_base - fp->_ptr);
#else
	return(BUFSIZ);	/* just a guess */
#endif
}

#else

#error unknown stdio implementation!

#endif