I'm working on some legacy code in which there are a lot of WriteLn(F, '...') commands scattered pretty much all over the place. There is some useful information in these commands (what information variables contain, etc), so I'd prefer not to delete it or comment it out, but I want to stop the program from writing the file.
Is there any way that I can assign the F variable so that anything written to it is ignored? We use the console output, so that's not an option.
Going back a long long time to the good old days of DOS - If you assign 'f' to the device 'nul', then there should be no output.
assign (f, 'nul')
I don't know whether this still works in Windows.
Edit:
You could also assign 'f' to a file - assignfile (f, 'c:\1.txt') - for example.
Opening the null device and letting output go there would probably work. Under DOS, the performance of the NUL device was astonishingly bad IIRC (from what I understand, it wasn't buffered, so the system had to look up NUL in the device table when processing each byte) but I would not be at all surprised if it's improved under newer systems. In any case, that's probably the easiest thing you can do unless you really need to maximize performance. If performance is critical, it might in theory be possible to override the WriteLn function so it does nothing for certain files, but unfortunately I believe it allows syntax forms that were not permissible for any user-defined functions.
Otherwise, I would suggest doing a regular-expression find/replace to comment out the WriteLn statements in a fashion that can be mechanically restored.
Related
What is the benefit of using paragraphs and sections for executing pieces of code, instead of using a subprogram instead? As far as I can see paragraphs and sections are dangerous because they have an non intuitive control flow, its easy to fall through and execute stuff you never meant to execute, and there is no variable (item) scoping, therefore it encourages a style of programming where everything is visible to everything else. Its a slippery soup.
I read a lot, but I could not find anything related to the comparative benefit of paragraphs/sections vs a subprogram. I also asked online some people in some COBOL forum, but their answers were along the lines of "is this a joke" or "go learn programming"(!!!).
I do not wish to engage in a discussion of stylistic preferences, everyone writes the way that their brain works, I only want to know, is there any benefit to using paragraphs/sections for flow control? As in, are there any COBOL operations that can be done only by using paragraphs/sections? Or is it just a remnant of an early way of thinking about code?
Because no other language I know of has mimicked that, so it either has some mechanical concrete essential reason to exist in COBOL, or it is a stylistic preference of the COBOL people. Can someone illuminate me on what is happening?
These are multiple questions... the two most important ones:
Are there any COBOL operations that can be done only by using paragraphs/sections?
Yes. A likely not complete list:
USE statements in DECLARATIVES can only apply to a paragraph or a section. These are used for handling file errors and exceptions. Not all compilers support this COBOL standard feature in full.
Segmentation (primary: a program that is only partially loaded in memory) is only possible with sections; but that is to be considered a "legacy feature" (at least I don't know of people actually using it this way explicitly); see the comment of Gilbert Le Blanc for more details on this
fall-through, many other languages have this feature with a kind of a switch statement (COBOL's EVALUATE, which is not the same as a common switch but can be used similar has an explicit break and no fall-through)
GO TO DEPENDING ON (could be recoded to achieve something similar with EVALUATE and then either PERFORM, if the paragraphs are expected to fall-through, which is not uncommon, then that creates a lot of extra code)
GO TO in general and especially nice - the old obsolete ALTER statement
PERFORM statement, format 1 "out-of-line"
file state is only shared between programs when you define it as EXTERNAL, and you often want to have a file state being limited to a single program
up to COBOL85: EXIT statement (plain without anything else, actually doing nothing else then a CONTINUE would)
What is the benefit of using paragraphs and sections for executing pieces of code, instead of using a subprogram instead?
shared data (I guess you know of programs with static data or otherwise (module)global data that is shared between functions/methods and also different source code files)
much less overhead than a CALL is
consistency:
you know what's in your code, you don't know what another program does (or at least: you cannot guarantee that it will do the same some years later exactly the same)
easier to extend/change: adding another variable (and also removing part of it, change its size) to a CALL USING means that you also have to adjust the called program - and all programs that call this, even when you place the complete definition in a copybook, which is very reasonable, this means you have to recompile all programs that use this
a section/paragraph is always available (it is already loaded when the program runs), a CALLed program may not be available or lead to an exception, for example because it cannot be loaded as its parameters have changed
less stuff to code
Note: While not all compilers support this you can work around nearly all of the runtime overhead and consistency issue when you use one source files with multiple program definitions in (possibly nested) and using a static call-convention. This likely gives you the "modern" view you aim for with scope-limitation of variables, within the programs either persistent (like local-static) when defined in WORKING-STORAGE or always passed when in LINKAGE or "local-temporary" when in LOCAL-STORAGE.
Should all code of an application be in one program?
[I've added this one to not lead to bad assumptions] Of course not!
Using sub-programs and also user-defined functions (possibly even nested providing the option for "scoped" and "shared" data) is a good thing where you have a "feature boundary" (for example: access to data, user-interface, ...) or with "modern" COBOL where you have a "language boundary" (for example: direct CALLs of C/Java/whatever), but it isn't "jut for limiting a counter to a section" - in this case: either define a variable which state is not guaranteed to be available after any PERFORM or define one for the section/paragraph; in both cases it would be reasonable to use a prefix telling you this.
Using that "separate by boundary" approach also takes care of the "bad habit of everything being seen by everyone" issue (which is in any case only true for "all sections/paragraphs in the same program).
Personal side note: I would only use paragraphs where it is a "shop/team rule" (it is better to stay consistent then to do things different "just because they are better" [still providing an option to possibly change the common rule]) or for GO TO, which I normally not use.
SECTIONs and EXIT SECTION + EXIT PERFORM [CYCLE] (and very rarely GOBACK/EXIT PROGRAM) make paragraphs nearly unnecessary.
very short answer. subroutines!!
Subroutines execute in the context of the calling routine. Two virtues: no parameter passing, easy to create. In some languages, subroutines are private to (and are part of) the calling (invoking) routine (see various dialects of BASIC).
direct answer: Section and Paragraph support a different way of thinking about programming. Higher performance than call subprogram. Supports overlays. The "fall thru" aspect can be quite useful, a feature rather than a vice. They may be necessary depending on what you are doing with a specific COBOL compiler.
See also PL/1, BAL/360, architecture 360/370/...
As a veteran Cobol dinosaur, I would say asking about the benefit is not the right question. I used paragraph (or section) differently than a subprogram. The right question in my opinion is when to use them logically. If I can make an analogy, if you have a Dog java class, you will write Dog-appropriate methods within it. If there's a cat involved, you may need a helper class. In this case the helper class is the subprogram. Though, you can instead code the helper class methods inside the Dog class, but that will be bad coding.
In any other language I would recommend putting self contained functions into subroutines.
However in COBOL not so much. If the code is very likely to be used in other programs then a subroutine is a good idea. Otherwise not!
The reason being the total lack of any checks on the number type or existence of passed parameters at compile time. Small errors in call statements lead to program crashes at run time. Limiting the use of sub-routines and carefully checking the calling code for errors makes for a more reliable program.
Using paragraphs any type mismatch will be flagged at compile time, or, an automatic conversion will occur.
I am responsible for converting an old UNIX based COBOL batch application that was developed by a consultant back in the 1990s to a Windows environment but still in COBOL using Microfocus (Eclipse, etc).
This is a pretty straight-forward task except for one little glitch.
The old application never did any explicit file handling within the COBOL. That is there are no FDs, OPENs, READs, WRITEs or CLOSE commands in the COBOL programs. Instead they wrote a C program that would do one of those different functions based on parameters passed to it (including, but not limited to file name, rec length, and the function desired.)
I would like to rewrite that subroutine in COBOL, which would require very little modifications to the COBOL main programs being converted. That is, it would still call that subroutine, but it would now be in COBOL instead of C.
But the challenge is how to write that subroutine so that it is able to act on most any file. I would think I have to go the route of variable length records because they could literally be any length up to to-be-determined maximum size, but seems like it would be vulnerable to error (as it tries to open different types of files).
Does anybody have any experience on this or ideas on a task like this? If not,l I may have to go the blunt force route of replacing each call statement to that subroutine with the specific COBOL command (Open, Read, etc) that needs to be performed and obviously FD and SELECT for every file would need to be added to the main program.
Thanks in advance.
You might be able to
CALL "subprogram" USING fd-name
where fd-name is
FD fd-name.
...
So, yes? maybe?, you might be able to pull off a subprogram that can take generic COBOL files. But, then you get into matching record layouts and other fun things, so, be wary. This might not work COBOL to COBOL, but it does work COBOL to C and back, as you end up passing a reference to the file control block.
You'll likely be better off looking into stock system libraries. Things like CBL_OPEN_FILE and CBL_READ_FILE if they are available. This will give you a much closer match to streaming IO that will be assumed in the current C subprogram.
Or, as Bill is suggesting in the comments, try and figure out why C was used and if you don't want the foreign functions, just dig in and write new COBOL procedures, as that will likely read better in the end.
The goto statement is taboo at my work.
So the following question is born...
Is there a situation possible where a goto is the only valid solution?
Originally GOTO was added to Pascal for error handling, including inter procedural forms that Borland(/Embarcadero) never implemented (example: GOTOing from a inner procedure to the parent), just like Borland never implemented other inner function functionality like passing inner functions to procedure-typed parameters.(*)
In that way GOTO can be considered the precursor to exceptions.
There still some practical uses: The last time I checked, jumping out of a nested IF statement with goto was still faster in Delphi then letting the code exit from a nested if naturally.
Optimizations like these are sometimes used in e.g. compression code, and other complex tree processing code with deeply nested loops or conditional statements.
Such routines often still use goto for errorhandling, because it is faster. (exceptions are not only slow, but their border conditions inhibit some optimizations).
One could see this as part of the plain Pascal level of Object Pascal, just like C++ still allows plain C nearly completely.
(of course, since the optimized compression code in Delphi is only delivered in .o form, it is hard to find examples in the Delphi codebase. The JPEG code has some, but that is a C translation)
(*) Original pascal, and IIRC even Turbo Pascal doesn't allow prematurely exiting a procedure with EXIT. Same for CONTINUE and BREAK.
Is there a situation possible where a GOTO is the only valid solution?
I suppose it depends on what you mean by valid. I suppose you are asking if there exists a program that can only be written with the use of the goto statement. In which case the answer is that there is no such program. Delphi is Turing complete with or without the goto statement.
However, if we are prepared to widen the discussion to include other languages, there are situations where goto is a good solution, even the best solution. The scenario that most commonly comes to mind is implementing tidy-up and error handling in languages without structured exception handling. If you peruse the Linux source code you will find that goto is widely used. I expect that the same is true of the Windows source code.
Goto is very old. It predates sub-routines like functions and procedures! It is also very dangerous and can make your code less readable (to others, or to yourself a few months later).
In theory it's not possible to have a situation where goto is required. I won't repeat the theory about Turing tape machines here, but using selection and iteration, you can re-order the code so in all possible input values the same output comes about.
In practice though, it's sometimes 'handy' and 'better readable' to 'jump away' from the flow of code in certain conditions, and that's where Exceptions come in. raise breaks away from the current execution, and jump to the closest finally or except section. This is safer because they work cascaded, and provide a better way to handle the context in case of one of these border conditions. (And there's also breakand abort and exit)
GOTO is never necessary. Any computable algorithm can be expressed with assignment and the combination of IF...THEN, BEGIN...END, and your choice of WHILE...DO...END or REPEAT...UNTIL. You don't even need subroutines. :)
This is known as the structured program theorem.
For a proof, see the 1966 paper, Flow Diagrams, Turing Machines and Languages with Only Two Formation Rules (PDF) by Corrado Böhm and Giuseppe Jacopini.
Something like 15 years ago I used the goto statement in Delphi to convert one of Bob Jenkins's hash functions from C to Pascal. The C function has a switch() statement without breaks after each case, and you can't do that with Pascal's case statement. So I converted it into a bunch of Pascal labels and gotos. I guess you would still have to do it the same way with the newest Delphi versions.
Edit: I guess using gotos would still be a reasonable way to do this. Gets the job done, easy to understand, limited to a short block of code, not dangerous.
I'm developing an application that parses Cobol programs. In these programs some respect the traditional coding style (programm text from column 8 to 72), and some are newer and don't follow this style.
In my application I need to determine the coding style in order to know if I should parse content after column 72.
I've been able to determine if the program start at column 1 or 8, but prog that start at column 1 can also follow the rule of comments after column 72.
So I'm trying to find rules that will allow me to determine if texts after column 72 are comments or valid code.
I've find some but it's hard to tell if it will work everytime :
dot after column 72, determine the end of sentence but I fear that dot can be in comments too
find the close character of a statement after column 72 : " ' ) }
look for char at columns 71 - 72 - 73, if there is not space then find the whole word, and check if it's a key word or a var. Problem, it can be a var from a COPY or a replacement etc...
I'd like to know what do you think of these rules and if you have any ideas to help me determine the coding style of a Cobol program.
I don't need an API or something just solid rules that I will be able to rely on.
I think you need to know the COBOL compiler for each program. Its documentation should tell you what conventions/configurations/switches it uses to decide if the source code ends at column 72 or not.
So.... which compiler(s)?
And if you think the column 72 issue is a pain, wait till you get around to actually parsing the COBOL itself. If you are not well prepared to handle the lexical issues of the language, you are probably very badly prepared to handle the syntactic ones.
There is no absolutely reliable way to determine if a COBOL program
is in fixed or free format based only on the source code. Heck it is sometimes difficult to identify
the programming language based only on source code. Check out
this classic polyglot - it is valid under 8 different language compilers. That
said, you could try a few heuristics that might yield
the correct answer more often than not.
Compiler directives imbedded in source code
Watch for certain compiler directives that determine code format.
Unfortunately, every compiler vendor uses their own flavour of directive.
For example, Microfocus COBOL uses the
SOURCEFORMAT directive. This directive will appear near the top of the program so a short pre-scan
could be used to find it. On the other hand, OpenCobol uses >>SOURCE FORMAT IS FREE and
>>SOURCE FORMAT IS FIXED to toggle between free and fixed format, different parts of the same program
could be formatted differently!
The bottom line here is that you will have to support the conventions of multiple COBOL compilers.
Compiler switches
Source code format can be also be specified using a compiler switch. In this case, there are no concrete
clues to go on. However, you can be reasonably sure that the entire source program will be either
fixed or free. All you can do here is guess. Unless the programmer is out to "mess with
your head" (and some will), a program in free format will have the keywords IDENTIFICATION DIVISION or ID DIVISION, starting before column 8.
Every COBOL program will begin with these keywords so you can use them as the anchor point for determining code format in the
absence of imbedded compiler directives.
Warning - this is far from fool proof, but might be a good start.
There won't be an algorithm to do this with 100% certainty, because if comments can be anything, they can also be compilable COBOL code. So you could theoretically write a program that means one thing if the comments are ignored, and something else entirely if the comments are treated as part of the COBOL.
But that's extremely unlikely. What's most likely to happen is that if you try to compile the code under the wrong convention, it will simply fail. So the only accurate way to do this is to try compiling/parsing the program one way, and if you come to a line that can't make sense, switch to the other style. You could also support passing an argument to the compiler when the style is already known.
You can try using heuristics like what you've described, but that will never be totally accurate. The most they can give you is a probability that the code is one or the other style, which will increase as they examine more and more lines of code. They could be useful for helping you guess the style before you start compiling, or for figuring out when the problem is really just a typo in the code.
EDIT:
Regarding ideas for heuristics, it's hard to say. If there were a standard comment sigil like // or # in other languages, this would be a lot easier (actually, there is, but it sounds like your code doesn't follow this convention). The only thing I can think of would be to check whether every line (or maybe 99% of lines, and not counting empty lines or lines commented with *) has a period somewhere before position 72.
One thing you DON'T want to do is apply any heuristics to the part after position 72. That is, you don't want to be checking the comments to see if they're valid COBOL. You want to check what you know is COBOL first, and see if that works by itself. There are several reasons for this:
Comments written in English are likely to have periods and quotes in them, so your first and second bullet points are out.
Natural languages are WAY harder to parse than something like COBOL.
The comments could easily have COBOL in them (maybe someone commented out the previous version of the line).
An important rule for comments is that they should never affect what the program does. If changing the comments can change how the program is compiled, you violate that.
All that in mind, my opinion is that you shouldn't use heuristics at all. You should always try to compile the program under both conventions unless one is explicitly specified. There's a chance that code will compile successfully under both conventions, and then you'll have two different programs and no way to tell which one is correct.
If that happens, you need to compare the two results (perhaps with a hash or something) to see if they're the same program. If they're the same, great, but if not, you'll need to force the user to explicitly choose a convention.
Most COBOL compilers will allow you to generate and analyze the post text manipulation phase.
The text preprocessor output can be seen (using OpenCOBOL for the example)
cobc -E program.cob
The text manipulation processor deals with any COPY ... REPLACING compiler directives, as well as converting SOURCE FORMAT IS FIXED (with line continuations, string literal concatenations, comment line removal, among other things) to the actual free format that the compiler lexical analyzer needs. A lot of the OpenCOBOL toolkits (Cross referencer and Animator, to name two) use source code AFTER the preprocessor pass. I don't think you'll lose any street cred if your parser program relies on post processed source code files.
can any one please say what is use of inline keyword in delphi
It is a hint to the compiler that the function/procedure should be (if possible) inlined, ie when you call it it should be expanded like a macro instead of being called.
This is an optimization for (very) small functions where the overhead of a call would be significant. You will find many examples in for example windows.pas
What actually happens depends on the complexity of the function, public/private access and your Delphi version.
It tells the compiler to generate code for the inline; routine on the place where it is called, instead of jumping to the routine and back.
For procedures that translate to very short assembler, this can be a benefit to performance, because the actual code is relatively short compared to the parameter preparation, the actual calling and the procedure prologue/epilogue.
If the procedure is too long, it can be a brake on performance though, and blow up your code gigantically. The "Auto" setting should make this decision for you, but in specific cases, you can locally set {$inline to on to force it. (e.g. for C macros translated to pascal functions, like the zlib functions to work with bitstreams )
Others have answered what inline does, but I just wanted to point out that there is a Compiler option to set inline on, off, or auto. Check out "Calling Procedures and Functions" in the D2009 docs for a very good explanation of the mechanics of inline. Here's the link to the online docs:
Delphi Online Docs for inline
It's borrowed from C in that it tells the compiler that this is a short routine that is frequently called and it recommends that the compiler treats the function as a macro and integrates the function code directly into the program at the point called rather than use a function call.
This gives faster code because there is no function call overhead, but at the expense of a larger program. Note too that like in C this is a recommendation to the compiler, it doesn't actually have to do so and the optimiser may override you.
Where to do this? Well like loop unwinding it's a technique that is very rarely of use nowadays. The classic place to use this is deep in a nested structure that is real-time critical, such as rendering code in a graphics application where a few machine calls shaved on each iteration can increase your screen refresh rate.
Press Ctrl + Alt + C (Entire CPU debug window) while debugging in Delphi, before call your inline function. And you will see that inline functions starts without "call" and wo jumping to another address. It's optimization feature.