BSD 1 development

[unix-history] / portlib / ungetc.c

# include       "iodec.h"

/**
**     return a single character to the io buffer
**/

ungetc(c, fn)
char    c;
int     fn;
{
       register struct fileps  *fp;
       extern int              __backup;
       extern int              f_log, cin;

       if (fn < 0 || fn >= MAXFILES)
               __error("ungetc: illegal file number %d", fn);
       fp = &__filehdr[fn];
       if (fp->wrflag == 2)
               __error("ungetc: file %d not open for reading", fn);
       if (fp->wrflag == 0)
               __makbuf(fn, 0);
       if (fp->bptr == fp->pbuff)
               __error("ungetc: file %d: peek buffer full", fn);
       if (f_log > 0 && fn == cin)
               __backup++;
       *--fp->bptr = c;
       fp->nchars++;
       return (c);
}