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Jim
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 Posted: Fri Dec 12, 2003 9:52 am Post subject: implicit declaration |
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im very new to c++ and am trying to compile a school project... my
only error is an implicit declartion error. my question is, what
exactly is an implicit declaration? i can't fix it cuz i dunno what
it is. whats worse is it's in code my professor gave to us... i
didn't write it. so debugging her code is twice as hard.
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Francis Glassborow
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| Posted: Fri Dec 12, 2003 7:01 pm Post subject: Re: implicit declaration |
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In article <cd155d8b.0312112138.59163c6d (AT) posting (DOT) google.com>, Jim
<gsmcret3 (AT) Juno (DOT) com> writes
| Quote: | im very new to c++ and am trying to compile a school project... my
only error is an implicit declartion error. my question is, what
exactly is an implicit declaration? i can't fix it cuz i dunno what
it is. whats worse is it's in code my professor gave to us... i
didn't write it. so debugging her code is twice as hard.
|
Did she ask you to debug it or did she give it to you as working code?
The closest thing that C++ has to implicit declarations are for compiler
generated default ctor, copy ctor, copy assignment and dtor for a class.
However I am suspicious that what you actually have been given is pre
C99 C source code because C used to allow the compiler to deduce a
function declaration from a use (I think we removed that from the
current version of C). Such deductions were very error prone because
they most often occur as a consequence of forgetting to #include a
header file.
C++ has never allowed deduced function declarations and has always
required a function declaration in the form that C calls a function
prototype.
The above probably does not make much sense at the moment. However try
compiling her code as C rather than as C++. If that works make a mental
note that your instructor sometimes provides poor quality code (maybe
just to test whether you identify it as such) In addition she may not be
entirely clear as to the difference between C and C++.
--
Francis Glassborow ACCU
Author of 'You Can Do It!' see http://www.spellen.org/youcandoit
or http://www.robinton.demon.co.uk
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Carlos Moreno
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| Posted: Sat Dec 13, 2003 1:55 am Post subject: Re: implicit declaration |
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Jim wrote:
| Quote: | im very new to c++ and am trying to compile a school project... my
only error is an implicit declartion error. my question is, what
exactly is an implicit declaration? i can't fix it cuz i dunno what
it is. whats worse is it's in code my professor gave to us... i
didn't write it. so debugging her code is twice as hard.
|
Without seeing the actual compiler error and the code and/or
some more information, we can't be 100% certain.
But this sounds to me like the code is calling a function
without providing a prototype. This is legal in C (though
good compilers typically issue a warning), but not in C++.
Every function you call must have been declared prior to
the first use.
HTH,
Carlos
--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Ben Hutchings
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| Posted: Sat Dec 13, 2003 2:02 am Post subject: Re: implicit declaration |
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Jim wrote:
| Quote: | im very new to c++ and am trying to compile a school project... my
only error is an implicit declartion error. my question is, what
exactly is an implicit declaration? i can't fix it cuz i dunno what
it is. whats worse is it's in code my professor gave to us... i
didn't write it. so debugging her code is twice as hard.
|
Without seeing the code that produces the error, and the exact error
message, I can only guess at what the error might be.
However, I think the problem is that the code is calling a function
for which no declaration has been given. Perhaps you forgot a
necessary #include directive?
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John Potter
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| Posted: Sat Dec 13, 2003 2:21 am Post subject: Re: implicit declaration |
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On 12 Dec 2003 14:01:04 -0500, Francis Glassborow
<francis (AT) robinton (DOT) demon.co.uk> wrote:
| Quote: | However I am suspicious that what you actually have been given is pre
C99 C source code because C used to allow the compiler to deduce a
function declaration from a use (I think we removed that from the
current version of C). Such deductions were very error prone because
they most often occur as a consequence of forgetting to #include a
header file.
C++ has never allowed deduced function declarations and has always
required a function declaration in the form that C calls a function
prototype.
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Good guess. That is a gcc-2.95 error message.
int main () {
f();
}
g++ junk.cpp
junk.cpp:2: implicit declaration of function `int f(...)'
John
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