.\" $Header$ .TH LIBPC VII .ad .SH NAME libpc \- library of external routines for Pascal programs .SH SYNOPSIS .ta 11 const bufsize = ?; .br type br1 = 1..bufsize; .br br2 = 0..bufsize; .br br3 = -1..bufsize; .br ok = -1..0; .br buf = packed array[br1] of char; .br alfa = packed array[1..8] of char; .br string = ^packed array[1..?] of char; .br filetype = file of ?; .br long = record high,low:integer end; {all routines must be declared extern} function argc:integer; .br function argv(i:integer):string; .br function environ(i:integer):string; .br procedure argshift; procedure buff(var f:filetype); .br procedure nobuff(var f:filetype); .br procedure notext(var f:text); .br procedure diag(var f:text); .br procedure pcreat(var f:text; s:string); .br procedure popen(var f:text; s:string); .br procedure pclose(var f:filetype); procedure trap(err:integer); .br procedure encaps(procedure p; procedure q(n:integer)); function perrno:integer; .br function uread(fd:integer; var b:buf; len:br1):br3; .br function uwrite(fd:integer; var b:buf; len:br1):br3; function strbuf(var b:buf):string; .br function strtobuf(s:string; var b:buf; len:br1):br2; .br function strlen(s:string):integer; .br function strfetch(s:string; i:integer):char; .br procedure strstore(s:string; i:integer; c:char); function clock:integer; .SH DESCRIPTION This library contains some often used external routines for Pascal programs. Two versions exist: one for the EM interpreter and another one that is used when programs are translated into PDP-11 code. The routines can be divided into several categories: .PP Argument control: .RS .IP argc 10 Gives the number of arguments provided when the program is called. .PD 0 .IP argv Selects the specified argument from the argument list and returns a pointer to it. This pointer is nil if the index is out of bounds (<0 or >=argc). .IP environ Returns a pointer to the i-th environment string (i>=0). Returns nil if i is beyond the end of the environment list (UNIX version 7). .IP argshift Effectively deletes the first argument from the argument list. Its function is equivalent to 'shift' in the UNIX shell: argv[2] becomes argv[1], argv[3] becomes argv[2], etc. It is a useful procedure to skip optional flag arguments. Note that the matching of arguments and files is done at the time a file is opened by a call to reset or rewrite. .PD .PP .RE Additional file handling routines: .RS .IP buff 10 Turn on buffering of a file. Not very useful, because all files are buffered except standard output to a terminal and diagnostic output. Input files are always buffered. .PD 0 .IP nobuff Turn off buffering of an output file. It causes the current contents of the buffer to be flushed. .IP notext Only useful for input files. End of line characters are not replaced by a space and character codes out of the ASCII range (0..127) do not cause an error message. .IP diag Initialize a file for output on the diagnostic output stream (fd=2). Output is not buffered. .IP pcreat The same as rewrite(f), except that you must provide the filename yourself. The name must be zero terminated. Only text files are allowed. .IP popen The same as reset(f), except that you must provide the filename yourself. The name must be zero terminated. Only text files are allowed. .IP pclose Gives you the opportunity to close files hidden in records or arrays. All other files are closed automatically. .PD .PP .RE String handling: .RS .IP strbuf 10 Type conversion from character array to string. It is your own responsibility that the string is zero terminated. .PD 0 .IP strtobuf Copy string into buffer until the string terminating zero byte is found or until the buffer if full, whatever comes first. The zero byte is also copied. The number of copied characters, excluding the zero byte, is returned. So if the result is equal to the buffer length, then the end of buffer is reached before the end of string. .IP strlen Returns the string length excluding the terminating zero byte. .IP strfetch Fetches the i-th character from a string. There is no check against the string length. .IP strstore Stores a character in a string. There is no check against string length, so this is a dangerous procedure. .PD .PP .RE Trap handling: .RS These routines allow you to handle almost all the possible error situations yourself. You may define your own trap handler, written in Pascal, instead of the default handler that produces an error message and quits. You may also generate traps yourself. .IP trap 10 Trap generates the trap passed as argument (0..252). The trap numbers 128..252 may be used freely. The others are reserved. .PD 0 .IP encaps Encapsulate the execution of 'p' with the trap handler 'q'. Encaps replaces the previous trap handler by 'q', calls 'p' and restores the previous handler when 'p' returns. If, during the execution of 'p', a trap occurs, then 'q' is called with the trap number as parameter. For the duration of 'q' the previous trap handler is restored, so that you may handle only some of the errors in 'q'. All the other errors must then be raised again by a call to 'trap'. .br Encapsulations may be nested: you may encapsulate a procedure while executing an encapsulated routine. .br Jumping out of an encapsulated procedure (non-local goto) is dangerous, because the previous trap handler must be restored. Therefore, you may only jump out of procedure 'p' from inside 'q' and you may only jump out of one level of encapsulation. If you want to exit several levels of encapsulation, use traps. See pc_emlib(VII) and pc_prlib(VII) for lists of trap numbers for EM machine errors and Pascal run time system errors. Note that 'p' may not have parameters. .PD .PP .RE UNIX system calls: .RS The routines of this category require global variables or routines of the monitor library libmon(VII). .IP uread 10 Equal to the read system call. Its normal name is blocked by the standard Pascal routine read. .PD 0 .IP uwrite As above but for write(II). .IP perrno Because external data references are not possible in Pascal, this routine returns the global variable errno, indicating the result of the last system call. .PD .PP .RE Miscellaneous: .RS .IP clock 10 Return the number of ticks of user and system time consumed by the program. .PD .PP .RE The following program presents an example of how these routines can be used. This program is equivalent to the UNIX command cat(I). .nf {$c+} program cat(input,inp,output); var inp:text; s:string; function argc:integer; extern; function argv(i:integer):string; extern; procedure argshift; extern; function strlen(s:string):integer; extern; function strfetch(s:string; i:integer):char; extern; procedure copy(var fi:text); var c:char; begin reset(fi); while not eof(fi) do begin while not eoln(fi) do begin read(fi,c); write(c) end; readln(fi); writeln end end; begin {main} if argc = 1 then copy(input) else repeat s := argv(1); if (strlen(s) = 1) and (strfetch(s,1) = '-') then copy(input) else copy(inp); argshift; until argc <= 1; end. .fi .PP Another example gives some idea of the way to manage trap handling: .nf program bigreal(output); const EFOVFL=4; var trapped:boolean; procedure encaps(procedure p; procedure q(n:integer)); extern; procedure trap(n:integer); extern; procedure traphandler(n:integer); begin if n=EFOVFL then trapped:=true else trap(n) end; procedure work; var i,j:real; begin trapped:=false; i:=1; while not trapped do begin j:=i; i:=i*2 end; writeln('bigreal = ',j); end; begin encaps(work,traphandler); end. .fi .SH FILES .IP /usr/em/mach/*/lib/tail_pc 20 .PD .SH "SEE ALSO" ack(I), pc_pem(VI), pc_prlib(VII), libmon(VII) .SH DIAGNOSTICS Two routines may cause fatal error messages to be generated. These are: .IP pcreat 10 Rewrite error (trap 77) if the file cannot be created. .PD 0 .IP popen Reset error (trap 76) if the file cannot be opened for reading .PD .SH AUTHOR Johan Stevenson, Vrije Universiteit. .br encaps: Ed Keizer, Vrije Universiteit.