User guide

78 CHAPTER 3. THE LIBRARY

returns TRUE if successful, and FALSE otherwise. A call of unrdch will alway s succeeds

the ﬁrst time after a call of rdch. It is useful in functions such as readn where singl e

character lookahead is necessary. See Section 3.3.1 for more detailed information.

wrch(ch) CIN:y, POS:y, NAT:y

This routine wri t e s the character ch to the currently selected output stream. If

output is to the screen, ch is transmitted immediately. It aborts (with code 189) if

there is a write failure.

writed(n, d) CIN:y, POS:y, NAT:y

writeu(n, d) CIN:y, POS:y, NAT:y

writen(n) CIN:y, POS:y, NAT:y

These rout i ne s output the integer n in decimal to the currently selected output

stream. For writed and writeu, the output is padded with leading spaces to ﬁll a ﬁeld

width of d characters. If writen is used or if d is to o small , the number is written

without padding. If writeu is used, n is regarded as an unsigned integer.

writehex(n, d) CIN:y, POS:y, NAT:y

writeoct(n, d) CIN:y, POS:y, NAT:y

writebin(n, d) CIN:y, POS:y, NAT:y

These routines output, repectively, the least signiﬁcant d hexadeci mal , octal or

binary digits of the integer n to the currently selected output st re am.

writes(str) CIN:y, POS:y, NAT:y

writet(str, d) CIN:y, POS:y, NAT:y

These routines out put the string str to the curr e ntly selected output stream. If

writet is use d, trailing spaces are added to ﬁll a ﬁeld width of d characters.

writef(format,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z)

CIN:y, POS:y, NAT:y

The ﬁr st argument (format) is a string that is c opi ed character by character to

the currently selected output stream until a substitution item such as %s or %i5 is

encountered when a value (usually the ne x t argument) is output in the speciﬁed format.

The substitution items are given in table 3.6.

When a ﬁel d width (denoted by n in the table) is r e q ui r ed , it is speciﬁed by a

single character, with 0 to 9 being represented by the corresponding digit and 10 to

35 represented by the letter s A to Z. Format characters are case insensitive but ﬁeld

width characters are not. A recent entension allows the ﬁeld width to be speciﬁed as a

decimal integer immediately following the percent, as in %12i meaning %iB.

Some examples of the %n.md substitution item are given below.

writef("%9.2d", 1234567) writes 12345.67

writef("%9.2d", -1234567) writes -12345.67

writef("%9.0d", 1234567) writes 1234567

writef("%9d", 1234567) writes 1234567

As an e x ampl e of how the %p substitution it em can be used, the following code: