8324155@max.u.washington.edu (08/30/90)
I'm hoping someone can help me with this (hopefully) easy question
about C++, and specifically Turbo C++. I have been learning C++ and using
the book "C++ Techniques and Applications" by Scott Robert Ladd, and when
I tried to compile one of his example programs with Turbo C++ I got a
"cannot overload 'main'" error message. It seems the compiler choked on
the author prototyping main (with the line: int main();
Is this a problem with Turbo C++, or is it not allowed in C++ and the
compiler that the author used just accepted it ? It works fine in Turbo
if I remove the prototype.
Thanks ahead of time, Mark Freybp@swamp.cis.ufl.edu (Brian Pane) (09/17/90)
In article <14227.26dc5b2f@max.u.washington.edu>, 8324155@max.u.washington.edu writes: |> |> |> |> I'm hoping someone can help me with this (hopefully) easy question |> about C++, and specifically Turbo C++. I have been learning C++ and using |> the book "C++ Techniques and Applications" by Scott Robert Ladd, and when |> I tried to compile one of his example programs with Turbo C++ I got a |> "cannot overload 'main'" error message. It seems the compiler choked on |> the author prototyping main (with the line: int main(); |> Is this a problem with Turbo C++, or is it not allowed in C++ and the |> compiler that the author used just accepted it ? It works fine in Turbo |> if I remove the prototype. |> |> Thanks ahead of time, Mark Frey Actually, main is "int main (int, char**)." If you declare main without argc or argv, the compiler realizes that you must be talking about some *other* main. Perhaps the author was using a machine without an operating system? :-) -Brian Pane ------------------------------------------------------------------------- Brian Pane University of Florida Department of Computer Science bp@swamp.cis.ufl.edu Class of 1991 "If you can keep your expectations |#ifdef OFFENDED_ANYONE tiny, you'll go through life |# include "disclaimer.h" without being so whiny" - Matt Groening |#endif -------------------------------------------------------------------------
saustin@bbn.com (Steve Austin) (09/17/90)
bp@swamp.cis.ufl.edu (Brian Pane) writes: >|> I tried to compile one of his example programs with Turbo C++ I got a >|> "cannot overload 'main'" error message. It seems the compiler choked on >|> the author prototyping main (with the line: int main(); >|> Is this a problem with Turbo C++, or is it not allowed in C++ and the >|> compiler that the author used just accepted it ? It works fine in Turbo >|> if I remove the prototype. >|> > >Actually, main is "int main (int, char**)." If you declare main without >argc or argv, the compiler realizes that you must be talking about some >*other* main. Perhaps the author was using a machine without an operating >system? :-) I don't think it make much sense at all to prototype main. You prototype a function in order to call it - I don't know what you would get if you tried to call main, but I bet it wouldn't be good. Also, if you do manage to prototye main, you will be asking for its name to be mangled, which will not please your linker. Other things wrong with the above definition "int main(int, char **)" are that main does not return a value (again, I'm not sure what would happen if you tried to return someting from main, but I bet it wouldn't be very meaningful). Also, main can have a third argument (at least on some systems) which is a "char **" and conatins the environment. Steve Austin
daniel@terra.ucsc.edu (Daniel Edelson) (09/17/90)
In article <59517@bbn.BBN.COM> saustin@bbn.com (Steve Austin) writes: >bp@swamp.cis.ufl.edu (Brian Pane) writes: > >>|> I tried to compile one of his example programs with Turbo C++ I got a >>|> "cannot overload 'main'" error message. It seems the compiler choked on >>|> the author prototyping main (with the line: int main(); >>Actually, main is "int main (int, char**)." .... From the 2.1 reference manual, section 3.4: ``The function main() may be defined as: int main() { /* ... */ } or int main(int argc, char * argv[]) { /* ... */ }'' From these two possible definitions it follows that main may have either or two prototypes: int main(); or int main(int argc, char * argv[]); Of course, if you prototyped main() to have no arguments and then defined it with two you must get an error. In C++ if your prototype and definition differ in a way that is significant to the overloading mechanism then you are declaring an overloaded function. (There may be exceptions to this rule, I'm probably just over-generalizing.) >> If you declare main without >>argc or argv, the compiler realizes that you must be talking about some >>*other* main. Perhaps the author was using a machine without an operating >>system? :-) You can certainly define main as ``int main() { /* ... */ }'' regardless of the operating system you're using. You simply can't access the invocation arguments. >I don't think it make much sense at all to prototype main. You prototype a >function in order to call it - I don't know what you would get if you tried to >call main, Again from section 3.4, ``The function main() may not be called from within a program.'' > but I bet it wouldn't be good. Also, if you do manage to prototye >main, you will be asking for its name to be mangled, which will not please >your linker. Not a problem. The compiler (to be useful) must be able to set the program's entry point. >Other things wrong with the above definition "int main(int, char **)" are that >main does not return a value (again, I'm not sure what would happen if you >tried to return someting from main, but I bet it wouldn't be very meaningful). Again, from section 3.4, ``A return statement in main() has the effect of calling exit() with the return value as the argument.'' >Also, main can have a third argument (at least on some systems) which is a >"char **" and conatins the environment. This is nonstandard, though prevalent. According to ANSI C freestanding systems need not support the environment. > Steve Austin Daniel Edelson | C++ virtual garbage recycler: daniel@cis.ucsc.edu, or | ``Recycle your garbage. Please ....!sun!practic!peren!daniel | don't make me clean up after you.''
leo@atcmp.nl (Leo Willems) (09/17/90)
From article <14227.26dc5b2f@max.u.washington.edu>, by 8324155@max.u.washington.edu: > > > > I'm hoping someone can help me with this (hopefully) easy question > about C++, and specifically Turbo C++. I have been learning C++ and using > the book "C++ Techniques and Applications" by Scott Robert Ladd, and when > I tried to compile one of his example programs with Turbo C++ I got a > "cannot overload 'main'" error message. It seems the compiler choked on > the author prototyping main (with the line: int main(); > Is this a problem with Turbo C++, or is it not allowed in C++ and the > compiler that the author used just accepted it ? It works fine in Turbo > if I remove the prototype. > > Thanks ahead of time, Mark Frey The annotated C++ ref man (E&S) is very explicit about main, amongst others it states: main() can not be overloaded and its calling conventions are implementation dependent, but two forms are recommended: main() and main(int, *char[]) So, however not stated explicitlly, as I see it you are not allowed to give a prototype for main. Hope this helps. Leo
enag@ifi.uio.no (Erik Naggum) (09/18/90)
Sorry for barging in -- I just started reading this newsgroup.
In article <659@atcmpe.atcmp.nl> leo@atcmp.nl (Leo Willems) writes:
The annotated C++ ref man (E&S) is very explicit about main, amongst
others it states: main() can not be overloaded and its calling conventions
are implementation dependent, but two forms are recommended:
main() and main(int, *char[])
Isn't also a third parameter, char *envp[], supported, so that the
list should read
main()
main(int, *char[])
main(int, *char[], *char[])
?
--
[Erik Naggum] Naggum Software; Gaustadalleen 21; 0371 OSLO; NORWAY
I disclaim, <erik@naggum.uu.no>, <enag@ifi.uio.no>
therefore I post. +47-295-8622, +47-256-7822, (fax) +47-260-4427william@syacus.acus.oz (William Mason) (09/19/90)
saustin@bbn.com (Steve Austin) writes: >bp@swamp.cis.ufl.edu (Brian Pane) writes: >I don't think it make much sense at all to prototype main. You prototype a >function in order to call it - I don't know what you would get if you tried to >call main, but I bet it wouldn't be good. Also, if you do manage to prototye >main, you will be asking for its name to be mangled, which will not please your >linker. While agreeing with the practical sentiment of this statement, I would like to suggest that there is a place for "prototyped main()-s" out there some where. Visualise an object oriented operating system ... (pretend it looks like a Mac or OS/2-PM, i.e. WIMPS-ish). Now in this environment I have a program "display.c" with overloaded and proto-typed main()-s. Each main() represents a different input for the display tool. For example: int main( postscript ){...} int main( troff ) {... } int main( GIFF ){...} Now, the actual implementation need not be one executable with multiple entry points (shades of FORTRAN). I would expect the compiler or pre-processor to generate a normal argc and argv style for the real main() and inside this the appropriate overloaded main() could be called. What is happening is that the (possibly GUI) shell is co-operating with the compiler to supply the correct switches so the real main() gets the correct information. The supposed shell could be primitive and only look at file type or it could use some resource file, etc. to effect the desired behaviour from "display". The important thing is that a lot of operating system interface messyness is done away with. Extensions to the model would allow environmental variables as main() parameters or defaults. E.g.: int main( Postscript_File pf, Device_type dt = $(TERM), ){ ... } Some of this functionality was part of the Pascal language, but only file parameters were allowed. The Microsoft Pascal extended this other types (it does prompt but I can't remember if it takes 'things' from an MS-DOS command line). Thanks for your time, William Mason ACUS Sydney.
rfg@NCD.COM (Ron Guilmette) (09/21/90)
In article <6932@darkstar.ucsc.edu> daniel@cis.ucsc.edu (Daniel Edelson) writes: >In article <59517@bbn.BBN.COM> saustin@bbn.com (Steve Austin) writes: >>I don't think it make much sense at all to prototype main. You prototype a >>function in order to call it - I don't know what you would get if you tried to >>call main, > >Again from section 3.4, ``The function main() may not be called from within a >program.'' Hummm... This looks like yet another one of these little C incompatabilities which didn't quite make it into the list of the incompatabilities in chapter 18. My favorite one is illustrated by the following example: void foobar (int irritating) { int irritating; } Put that in your C++ compiler! Then look for this in chapter 18. It ain't there. -- // Ron Guilmette - C++ Entomologist // Internet: rfg@ncd.com uucp: ...uunet!lupine!rfg // Motto: If it sticks, force it. If it breaks, it needed replacing anyway.
steve@taumet.com (Stephen Clamage) (09/21/90)
rfg@NCD.COM (Ron Guilmette) writes: > void foobar (int irritating) > { > int irritating; > } >Put that in your C++ compiler! Then look for this in chapter 18. It ain't >there. Try putting it in your ANSI C compiler. It won't work there either. "irritating" is defined twice in the same scope, which is illegal. If your C compiler allows this, report it to the vendor as a bug! -- Steve Clamage, TauMetric Corp, steve@taumet.com
hardin@hpindda.cup.hp.com (John Hardin) (09/22/90)
> Hummm... This looks like yet another one of these little C incompatabilities > which didn't quite make it into the list of the incompatabilities in > chapter 18. > > My favorite one is illustrated by the following example: > > void foobar (int irritating) > { > int irritating; > } > > Put that in your C++ compiler! Then look for this in chapter 18. It ain't > there. > > // Ron Guilmette - C++ Entomologist ---------- Sorry, perhaps I'm just being dense today, but I don't get your point. When I put the above code through an ANSI C compiler I get "x.c", line 3: warning: redeclaration of 'irritating' hides formal parameter while I get the following when I put it through my C++ compiler: CC: "x.C", line 3: error 1031: two declarations of irritating Could you please clarify? Thanks. John Hardin hardin@hpindgh.hp.com -----------
rfg@NCD.COM (Ron Guilmette) (09/22/90)
In article <461@taumet.com> steve@taumet.com (Stephen Clamage) writes: <rfg@NCD.COM (Ron Guilmette) writes: < <> void foobar (int irritating) <> { <> int irritating; <> } < <>Put that in your C++ compiler! Then look for this in chapter 18. It ain't <>there. < <Try putting it in your ANSI C compiler. It won't work there either. <"irritating" is defined twice in the same scope, which is illegal. ACK! I stand corrected. I though that was legal ANSI C. Apparently I was wrong. Sorry. <If your C compiler allows this, report it to the vendor as a bug! I just did. Thanks Steve. -- // Ron Guilmette - C++ Entomologist // Internet: rfg@ncd.com uucp: ...uunet!lupine!rfg // Motto: If it sticks, force it. If it breaks, it needed replacing anyway.