Example: sample PL/I program for debugging
The program below is used in various topics to demonstrate debugging tasks.
This program is a simple calculator that reads its input from a character buffer. If integers are read, they are pushed on a stack. If one of the operators (+ - * /) is read, the top two elements are popped off the stack, the operation is performed on them and the result is pushed on the stack. The = operator writes out the value of the top element of the stack to a buffer.
Before running PLICALC, you need to allocate SYSPRINT
to the terminal by entering the following command:
ALLOC FI(SYSPRINT) DA(*) REUSEMain program PLICALC
plicalc: proc options(main);
/*------------------------------------------------------------------*/
/* */
/* A simple calculator that does operations on integers that */
/* are pushed and popped on a stack */
/* */
/*------------------------------------------------------------------*/
dcl index builtin;
dcl length builtin;
dcl substr builtin;
/* */
dcl 1 stack,
2 stkptr fixed bin(15,0) init(0),
2 stknum(50) fixed bin(31,0);
dcl 1 bufin,
2 bufptr fixed bin(15,0) init(0),
2 bufchr char (100) varying;
dcl 1 tok char (100) varying;
dcl 1 tstop char(1) init ('s');
dcl 1 ndx fixed bin(15,0);
dcl num fixed bin(31,0);
dcl i fixed bin(31,0);
dcl push entry external;
dcl pop entry returns (fixed bin(31,0)) external;
dcl readtok entry returns (char (100) varying) external;
/*------------------------------------------------------------------*/
/* input action: */
/* 2 push 2 on stack */
/* 18 push 18 */
/* + pop 2, pop 18, add, push result (20) */
/* = output value on the top of the stack (20) */
/* 5 push 5 */
/* / pop 5, pop 20, divide, push result (4) */
/* = output value on the top of the stack (4) */
/*------------------------------------------------------------------*/
bufchr = '2 18 + = 5 / =';
do while (tok ^= tstop);
tok = readtok(bufin); /* get next 'token' */
select (tok);
when (tstop)
leave;
when ('+') do;
num = pop(stack);
call push(stack,num); /* CALC1 statement */
end;
when ('-') do;
num = pop(stack);
call push(stack,pop(stack)-num);
end;
when ('*')
call push(stack,pop(stack)*pop(stack));
when ('/') do;
num = pop(stack);
call push(stack,pop(stack)/num); /* CALC2 statement */
end;
when ('=') do;
num = pop(stack);
put list ('PLICALC: ', num) skip;
call push(stack,num);
end;
otherwise do;/* must be an integer */
num = atoi(tok);
call push(stack,num);
end;
end;
end;
return;TOK function
atoi: procedure(tok) returns (fixed bin(31,0));
/*------------------------------------------------------------------*/
/* */
/* convert character string to number */
/* (note: string validated by readtok) */
/* */
/*------------------------------------------------------------------*/
dcl 1 tok char (100) varying;
dcl 1 num fixed bin (31,0);
dcl 1 j fixed bin(15,0);
num = 0;
do j = 1 to length(tok);
num = (10 * num) + (index('0123456789',substr(tok,j,1))-1);
end;
return (num);
end atoi;
end plicalc;PUSH function
push: procedure(stack,num);
/*------------------------------------------------------------------*/
/* */
/* a simple push function for a stack of integers */
/* */
/*------------------------------------------------------------------*/
dcl 1 stack connected,
2 stkptr fixed bin(15,0),
2 stknum(50) fixed bin(31,0);
dcl num fixed bin(31,0);
stkptr = stkptr + 1;
stknum(stkptr) = num; /* PUSH1 statement */
return;
end push;POP function
pop: procedure(stack) returns (fixed bin(31,0));
/*------------------------------------------------------------------*/
/* */
/* a simple pop function for a stack of integers */
/* */
/*------------------------------------------------------------------*/
dcl 1 stack connected,
2 stkptr fixed bin(15,0),
2 stknum(50) fixed bin(31,0);
stkptr = stkptr - 1;
return (stknum(stkptr+1));
end pop;READTOK function
readtok: procedure(bufin) returns (char (100) varying);
/*------------------------------------------------------------------*/
/* */
/* a function to read input and tokenize it for a simple calculator */
/* */
/* action: get next input char, update index for next call */
/* return: next input char(s) */
/*------------------------------------------------------------------*/
dcl length builtin;
dcl substr builtin;
dcl verify builtin;
dcl 1 bufin connected,
2 bufptr fixed bin(15,0),
2 bufchr char (100) varying;
dcl 1 tok char (100) varying;
dcl 1 tstop char(1) init ('s');
dcl 1 j fixed bin(15,0);
/* start of processing */
if bufptr > length(bufchr) then do;
tok = tstop;
return ( tok );
end;
bufptr = bufptr + 1;
do while (substr(bufchr,bufptr,1) = ' ');
bufptr = bufptr + 1;
if bufptr > length(bufchr) then do;
tok = tstop;
return ( tok );
end;
end;
tok = substr(bufchr,bufptr,1); /* get ready to return single char */
select (tok);
when ('+','-','/','*','=')
bufptr = bufptr;
otherwise do; /* possibly an integer */
tok = '';
do j = bufptr to length(bufchr);
if verify(substr(bufchr,j,1),'0123456789') ^= 0 then
leave;
end;
if j > bufptr then do;
j = j - 1;
tok = substr(bufchr,bufptr,(j-bufptr+1));
bufptr = j;
end;
else
tok = tstop;
end;
end;
return (tok);
end readtok;Refer to the following topics for more information related to the material discussed in this topic.
- Related tasks
- Debugging a PL/I program in full-screen mode