_iob
#define STDIOP(iop) ((iop) >= &_iob[0] && (iop) < &_iob[_NFILE])
#define IOPIND(iop) ((iop) - &_iob[0])
FILE _iob[_NFILE] = {
FILE *_lastbuf = &_iob[_NFILE];
FILE _iob[_NFILE] = {
&_iob[0],
fp = &xfp->_iob;
fp = x##fp ? &x##fp->_iob : &_iob[0]
#define NEXTFP(fp) (x##fp ? fp = &(++x##fp)->_iob : ++fp)
FILE _iob; /* must be first! */