|
It creates functions which are strictly monolithic. It's not bad but it create impediments in further expansions or refactorizations of the function that uses it.
Goto to code outside the function containing it is problematic for the compilers, breaks modularity in C code as much as global variables do, and is completely undoable in OOP due to context changes.
All in all it may be a good solution but ultimately not worth the delayed troubles if not under very constrained circumstances.
GCS d-- s-/++ a- C++++ U+++ P- L+@ E-- W++ N+ o+ K- w+++ O? M-- V? PS+ PE- Y+ PGP t+ 5? X R+++ tv-- b+(+++) DI+++ D++ G e++ h--- ++>+++ y+++* Weapons extension: ma- k++ F+2 X
|
|
|
|
|
I would say your examples are good examples of misuse, and not problems with goto itself. I don't use goto myself, except in rare cases to short-circuit a function.
|
|
|
|
|
That's a nice spot to use goto, I have used it twice in my life precisely for that: later I ended up removing them due to a refactor that improved every aspect of those functions (performance, readability, debuggability).
That said, I don't discard it out of hand as it is a powerful tool. As TNCaver said "You think goto is evil: try writing Assembly programs without JMP" (it has been in my signature for years... and I do also write Assembly code so it was really appropriate).
GCS d-- s-/++ a- C++++ U+++ P- L+@ E-- W++ N+ o+ K- w+++ O? M-- V? PS+ PE- Y+ PGP t+ 5? X R+++ tv-- b+(+++) DI+++ D++ G e++ h--- ++>+++ y+++* Weapons extension: ma- k++ F+2 X
|
|
|
|
|
You can use goto to short-circuit time-constrained algorithms for academic or scientific purposes.
Don't use it anywhere else, especially not in a professional setting, or people will be strongly compelled to gut, rape and murder your code the first chance they get.
And can you really blame them for it?
|
|
|
|
|
den2k88 wrote: breaks modularity in C code
That is true for C, but not so much for C++. goto is context dependent in C++, it will call appropriate constructors/destructors. When used in local context it will not make the function/method monolithic. So if goto is so bad, you might be using a badly outdated language?
|
|
|
|
|
Plamen Dragiyski wrote: goto is context dependent in C++, it will call appropriate constructors/destructors.
Which is an Access Violation waiting to happen when the code changes.
Plamen Dragiyski wrote: So if goto is so bad, you might be using a badly outdated language?
And that would be?
GCS d-- s-/++ a- C++++ U+++ P- L+@ E-- W++ N+ o+ K- w+++ O? M-- V? PS+ PE- Y+ PGP t+ 5? X R+++ tv-- b+(+++) DI+++ D++ G e++ h--- ++>+++ y+++* Weapons extension: ma- k++ F+2 X
|
|
|
|
|
den2k88 wrote: Which is an Access Violation waiting to happen when the code changes.
How? If jumping outside block can causes access violation, then every "}" is potential access violation.
If you talk about inter-scope goto, that's is entirely different story. You can do that in C using signals. What will be the state in C++ after such goto it is indeed unknown, so that's one possible misuse of goto. But if all affected variables are on the stack (and in C++ they should be - all pointer should be wrapped into appropriate *_ptr object allocated on the stack), jumping outside of scope is completely safe. Jumping inside non-conditional scopes is also safe. Jumping inside anything else is a bad idea.
Jumping outside scope, can be realized by do-while wrapping:
do {
} while(false);
But it cannot be used inside loop/switch statement and it is utterly more ugly than goto.
|
|
|
|
|
den2k88 wrote: Which is an Access Violation waiting to happen when the code changes.
And you are claiming that cannot happen without gotos?
Or if those others occur they can only occur when another feature of the language is used correctly?
|
|
|
|
|
Looking to some MSDN examples, I never saw goto, I only saw things like this (also a kind of goto):
....
while(true)
{
if (!Method_1())
break;
...
if (!Method_N())
break;
...
}
...
It does not solve my Problem, but it answers my question
modified 19-Jan-21 21:04pm.
|
|
|
|
|
There are gotos in the source code for C# in places.
|
|
|
|
|
Hi,
RandyBuchholz wrote: It's a conditioned response.
That's exactly what it is. A few years ago I had to use some goto statements in a device driver written in C where the push/pop function prolog/epilog[^] was causing a performance reduction of between 30% - 40%. I could not find anything that matched the speed of the goto statement and left it in the production code.
High-performance code is almost always ugly.
RandyBuchholz wrote: Or is goto inherently and absolutely evil?
I would say that you do not need a goto statement 99.999% of the time. But I have used it at least ONE time in the past two decades where I feel it was necessary.
Best Wishes,
-David Delaune
|
|
|
|
|
I do not use goto in C++ programs while I use it in C ones. I do abuse of gotos in assembly code.
|
|
|
|
|
RandyBuchholz wrote: Have we developed an irrational fear of
Speak for yourself. 
Just look what I'm working on right now. Every opcode that starts with B is a branch (= goto).
; =========================================================================================
; BIOS Command selection
;
; Parameters:
; ---
;
; Returns:
; ---
; =========================================================================================
BIOS_Command: LDI hi(TxtEnterCommand)
STXD
LDI lo(TxtEnterCommand)
STXD
SEP R4
dw WriteLine
CMD_Repeat: LDI 00FFH ; get RS232 input, max. timeout
STXD
SEP R4
dw RS232InSoftware
IRX ; timeout?
LDX
BZ CMD_Skip
STXD ; echo input
STXD
SEP R4
dw RS232Out
IRX
LDX
SDI 006EH ; test input = n
BZ CMD_Exit
LDX
SDI 0079H
BNZ CMD_Repeat
LDI hi(TxtNewLine) ; announce BIOS CMD
STXD
LDI lo(TxtNewLine)
STXD
SEP R4
dw WriteLine
LDI hi(TxtNewLine)
STXD
LDI lo(TxtNewLine)
STXD
SEP R4
dw WriteLine
LDI hi(TxtCmdTitle)
STXD
LDI lo(TxtCmdTitle)
STXD
SEP R4
dw WriteLine
CMD_Prompt: LDI hi(TxtCmdPrompt) ; output the prompt
STXD
LDI lo(TxtCmdPrompt)
STXD
SEP R4
dw WriteLine
LDI 00H ; get RS232 input, no timeout
STXD
SEP R4
dw RS232InSoftware
LDI TRUE
PLO RF
IRX ; echo input
LDX
STXD
STXD
SEP R4
dw RS232Out
IRX
LDX ; test input = x
SDI 0078H
BZ CMD_Exit
LDX ; test input = X
SDI 0058H
BZ CMD_Exit
LDX ; test input = h
SDI 0068H
BZ CMD_Help
LDX ; test input = H
SDI 0048H
BZ CMD_Help
CMD_Invalid: LDI hi(TxtCmdInvalid) ; error message (invalid command)
STXD
LDI lo(TxtCmdInvalid)
STXD
SEP R4
dw WriteLine
BR CMD_Prompt
CMD_Help: LDI hi(TxtCmdHelp) ; help text
STXD
LDI lo(TxtCmdHelp)
STXD
SEP R4
dw WriteLine
LDI hi(TxtCmdHelp1)
STXD
LDI lo(TxtCmdHelp1)
STXD
SEP R4
dw WriteLine
BR CMD_Prompt
CMD_Skip: LDI hi(TxtSkipped)
STXD
LDI lo(TxtSkipped)
STXD
SEP R4
dw WriteLine
CMD_Exit: SEP R5
;------------------------------------------------------------------------------------------
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
I have no fears! 
My education is EE, and I still see registers (68xx architecture) in my head no matter what language I'm programming in. I don't actually see the code that way, it's just kind of a background image. It's amazing how many developers don't know that the only branching a CPU has is a goto.
|
|
|
|
|
Even one as unconventional as this one here.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
Sacrilege! You will goto hell for such thoughts!
Oh wait. Even hell has been refactored: while (true) burnInHellForever(); 
|
|
|
|
|
Not:
Quote: while (true) burnInHellForever();
while (false) burnInHellForever();
"true" believers go to heaven! 
|
|
|
|
|
I've not used the goto keyword in any of my C/C++/C# code over the last 20 years or so.
I routinely use break (goto's more civilized brother, as it were) to exit for loops early. I do this in cases where expressing the iteration as a for loop is more appropriate for the general case, and the break handles the exceptions. I don't tend to use continue nearly as much in similar situations; I'm not sure why.
I dislike when code uses exceptions as an exotic form of iteration/flow control. My least favorite mechanism would have to be setjmp()/longjmp(), which is a very old C runtime library mechanism that fortunately doesn't see a lot of use today.
Software Zen: delete this;
|
|
|
|
|
Yup, been there. Just after starting my first "real" job in the early PC days (company upgraded the network file server to a bleeding-edge IBM AT just after I started), I had to debug a DOS BASIC program that implemented the equivalent of function/subroutine calls by saving the return line in a variable (all global, single letter optionally followed by a single digit), setting an ON ERROR GOTO for the desired function, then forcing an exception, and using the same mechanism with the saved return line value to return. Written by a nuclear physicist, no REMarks in the code - just the physicist's hand-scrawled notes. I might be mistaken, but I seem to recall that there was a way to set the ON ERROR GOTO for different target lines depending on the exception code generated, and this was used to pick which "function" to "call" at various locations in the code.
Today, he probably would have coded the entire thing as a single Excel macro with just Row-Column cell references and of course, no labels, headings, etc. 
|
|
|
|
|
I think it depends on the context. In C it's not so bad and I can think of a few notable examples where it is used. One instance I found rather humorous and posted in a coding 'hall of fame' page we used to have here, is in the default procedure of Windows v3.0 and the label used was "IcantBelieveIactuallyUsedAgoto." The source code of it was published in an old book by Peter Norton on windows programming.
On the other hand, I think using goto in C++ is a really bad idea. Since objects are automatically deleted when they fall out of scope, a goto could result in memory leaks if not used very carefully. As far as I am concerned this opinion is not based on fear nor is it irrational. YMMV.
|
|
|
|
|
Back in 1988 when I went to university to study computer science we were taught that we were never
to use goto except in one particular circumstance with COBOL.
We were strictly taught structured programming and in the first year had 2 hours of computer time each week. Most of our work was done on paper.
Fast forward to now and I am quite happy to use a return statement in code which in essence is a goto.
I think in principle it's good to learn the rules of structured programming to know when it is ok to break those rules.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
|
|
|
|
|
GuyThiebaut wrote: use a return statement in code which in essence is a goto.
No, it's that other thing, calling and returning from subroutines. A totally different animal, down to the machine code of the processor.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
|
|
|
|
|
GuyThiebaut wrote: Back in 1988
GuyThiebaut wrote: the first year had 2 hours of computer time each week. Most of our work was done on paper.
I remember those days well!...being a CS major from around '87 to '89 when my part-time afternoon job turned into full-time, which meant almost no lab time. I quit school for 10 years and finally went back and finished. During my 10 year hiatus, I had very little contact with computers so coming back to it after a decade I was more than a little pleased to find that I could finally do homework at home...even in the wee hours of the morning!
Somewhere in a box, in a closet, are notebooks with handwritten C, Pascal, and Fortran homework assignments. I also have some greenbar printouts with notes/grade. Deliverables for an assignment were typically handwritten pseudo-code and/or flowchart and the printout which contained source code and results. That junk probably won't make the next move!
It amazes me now to think about how different it was to learn programming back then. Nowadays, an answer to a question is usually just a few clicks away, back then we relied on books, our own wits, and occasionally teachers/aides who sometimes knew little more than we did.
Thanks for the memories!
"Go forth into the source" - Neal Morse
|
|
|
|
|
Thanks for the post!
I am ambivalent as to whether I would rather learn CS now or back in the 80's.
Back in the 80's there was no WWW or everything that came with it(given the internet did exist with JANET being the network we had access to).
In some ways I think people have it harder nowadays because there is so much more to learn.
On the other hand a kid with a laptop and network connection can easily educate themselves, to the same level I was at when I graduated, before they even start their course in CS.
I think we expect more of graduates nowadays than we did back in the 90's when it was a given that your first few years would be on the job training and you understood that when you graduated that you basically knew very little.
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
|
|
|
|
|
For several years programmers have had OOAD and OOP pounded into their heads, and goto is an inherently structured code construct. If you use goto in an object oriented program, you are creating spaghetti code, which is why that particular reflex exists.
"There are three kinds of lies: lies, damned lies and statistics."
- Benjamin Disraeli
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
