C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  delete [] followed by expression with commas          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Andrew Marlow Guest Posted: Tue May 22, 2007 12:11 am    Post subject: delete [] followed by expression with commas I have just come across some code like this: delete [] a, b, c; Is it the same as: delete [] a; delete [] b; delete [] c; I am not sure. I am wondering if maybe the [] only gets applied to the 'a' and the 'b' and 'c' are deleted without the '[]'. Or maybe the 'a, b, c' bit is evaluated to just 'a' and the 'b' and 'c' don't get deleted at all. Can someone shed some light for me please? -- Andrew Marlow http://www.andrewpetermarlow.co.uk There is an emerald here the size of a plover's egg! Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Daniel T. Guest Posted: Tue May 22, 2007 3:35 am    Post subject: Re: delete [] followed by expression with commas On May 21, 8:11 pm, Andrew Marlow <use...@marlowa.plus.com> wrote: Quote: I have just come across some code like this: delete [] a, b, c; Is it the same as: delete [] a; delete [] b; delete [] c; No. It's the same as: a; b; delete [] c; Unless the comma operator has been messed with. -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Alberto Ganesh Barbati Guest Posted: Tue May 22, 2007 3:36 am    Post subject: Re: delete [] followed by expression with commas Andrew Marlow ha scritto: Quote: I have just come across some code like this: delete [] a, b, c; Is it the same as: delete [] a; delete [] b; delete [] c; I am not sure. I am wondering if maybe the [] only gets applied to the 'a' and the 'b' and 'c' are deleted without the '[]'. Or maybe the 'a, b, c' bit is evaluated to just 'a' and the 'b' and 'c' don't get deleted at all. Can someone shed some light for me please? The comma up there is a comma operator, which is parsed with a precedence lower than delete[]. According to C++ grammar rules, "delete[] a, b, c" is thus evaluated as "((delete[] a), b), c". So 'a' gets deleted, the result of the delete-expression (which has type void) is discarded, 'b' is also discarded and the entire expression evaluates to 'c'. HTH, Ganesh -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Erik Max Francis Guest Posted: Tue May 22, 2007 3:40 am    Post subject: Re: delete [] followed by expression with commas Andrew Marlow wrote: Quote: I have just come across some code like this: delete [] a, b, c; Is it the same as: delete [] a; delete [] b; delete [] c; I am not sure. I am wondering if maybe the [] only gets applied to the 'a' and the 'b' and 'c' are deleted without the '[]'. Or maybe the 'a, b, c' bit is evaluated to just 'a' and the 'b' and 'c' don't get deleted at all. Can someone shed some light for me please? No. There is only one argument deleted in a delete/delete [] statement. When you write delete[] a, b, c; you're using the comma operator. This is the same thing as delete[] (a, b, c); The comma operator expression evaluates to the last sub-expression, so this is the same as delete[] c; Don't use commas at all; use delete[] a; delete[] b; delete[] c; -- Erik Max Francis && max (AT) alcyone (DOT) com && http://www.alcyone.com/max/ San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis If love is the answer, could you rephrase the question? -- Lily Tomlin [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Matt Messina Guest Posted: Tue May 22, 2007 3:42 am    Post subject: Re: delete [] followed by expression with commas Andrew Marlow <usenet (AT) marlowa (DOT) plus.com> wrote: Quote: I have just come across some code like this: delete [] a, b, c; Hopefully presented as an example of what not to do. :-) Quote: Is it the same as: delete [] a; delete [] b; delete [] c; delete and delete[] have very high precedence (same as pre-increment and dereference). Comma has the lowest precedence. But if you didn't happen to know that, you could ask your compiler: int main() { int a; int* b; delete a, b; } If you don't trust your compiler, ask Comeau tryitout. -- Matt Messina messina (AT) yahoo (DOT) com -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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