Hi Oren, On Wed, May 18, 2011 at 07:36:03AM -0700, Foster Boondoggle wrote: > > Hi Adam99 - Did you ever get a reply to this? I have the exact same problem > (indeed, with SqMatrix and Matrix, though I had though I wrote the class > many years ago!) I can't seem to get it to compile in any form with the > latest gcc. Yes, that question was answered by Ian, see e.g. http://old.nabble.com/Re%3A-invalid-cast-of-an-rvalue-expression-p23106343.html The point is: It is illegal C++ :-) Old compilers (like g++ 4.1.2) accepted such constructs, but the new gcc-versions detect it as failure In addition: what this line does, is the following: - take "this", a pointer to a "const SqMatrix" - convert it to a Pointer to a "Matrix" (already problematic: you remove the const-ness here...) - take the element and multiply it with "sm" - convert the pointer to a constant reference to a SqMatrix - create a copy of this reference and return it. that sounds a bit complex to me. In order to propose a solution, we would need more information (e.g. how are the classes defined? is SqMatrix derived from Matrix? are there any Conversion-Operators / Copy-Constructors defined which can be used for this conversions? The easiest solution for this code segment would be to add a new copy-constructor to SqMatrix: class SqMatrix { public: explicit SqMatrix(const Matrix &m) : ...{ assert(m.Rows() == m.Columns()); .... } }; which verifies that m is really square, and then creates a SqMatrix from m (I added "explicit" in order to block implicit type-conversions Matrix -> SqMatrix -- this constructor has to be called directly). With that, you could rewrite your code-segment as SqMatrix operator * (const SqMatrix &sm) const { return SqMatrix(*(const Matrix *)this * sm); } which would be save (the type-conversion is cleanly done) and portable. (however, as I don't know the full code, may be this solution poses other problems?) Axel (I'm not adam99 ;-)) > > adam99 wrote: > > > > > > > > I am getting a following error on g++ 4.1.2 > > > > > > SqMatrix.h: In member function 'SqMatrix SqMatrix::operator*(const > > SqMatrix&) const': > > SqMatrix.h:91: error: invalid cast of an rvalue expression of type > > 'Matrix' to type 'const SqMatrix&' > > > > > > for the following code segment > > > > SqMatrix operator * (const SqMatrix &sm) const { > > return (const SqMatrix &) (*(Matrix *)this * sm); } > > > > > > this error did not seem to appear on g++ 3.4.6. Do you know what could be > > the problem? > > > > Thanks > > > > > > > > > > -- > View this message in context: http://old.nabble.com/invalid-cast-of-an-rvalue-expression-tp23105605p31647448.html > Sent from the gcc - Help mailing list archive at Nabble.com. >
