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<html><!-- Mirrored from c-faq.com/misc/cplusplus.nr.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 08:02:55 GMT --><head><title></title></head><body>From: Noone Really <nooneatnowhere@earthlink.net><br>Newsgroups: comp.lang.c<br>Subject: Re: FAQ 20.27: Is C++ a superset of C? Can I use a C++ compiler to compile C code?<br>Date: Sun, 31 Jan 1999 17:47:25 -0700<br>Message-ID: <36B4F99D.97D84E5D@earthlink.net><p>Larry Weiss wrote:<br>> FAQ 20.27 promises that there are "some legal C constructs which<br>> are not legal C++". I would like to see some examples of this.<br><p>By C, the FAQ meant, and I guess we still mean, the current language,not proposals for C9x. <p>There are a number of these. I once worked out a pretty big list, butdo not remember it now. However, you just asked for examples:<p>1) auto conversion from <TT>void *</TT> to any object/incomplete type:<pre> void *one; char *two =one;</pre><p>2) new keywords (a number of these)<pre> int new;</pre><p>3) due to structs becoming scoped<pre> struct x { struct y { int z; } w; }; struct y v;</pre><p>4) due to struct tags becoming typedefs:<pre> struct y {int z;}; int f(int(y)); f(3);</pre><p>5) due to prototypes being required<pre> int f(); f(3);</pre><p>6) implicit int rules<pre> main(){}</pre><p>7) Recursive call to main<p>8) Due to // comments<pre> int x = 2//*why???*/2; int y;</pre><p>> FAQ 20.27 also promised that "the two also define the meaning<br>> of some common constructs differently". I would like to see<br>> some examples of that.<p>A few examples which come to mind immediately:<p>1) Due to // comments:<pre> int x = 2//*why???*/2 ;</pre><p>2) due to character literals being type <TT>char</TT> and not <TT>int</TT> etc.<br>So, if sizeof(int) != 1, <pre> sizeof('a')</pre>differs in the two languages<p>3) Due to struct scopes<pre> struct y {int z;}; { struct x { struct y { char z; } w; }; struct y v; return sizeof v.z; }</pre><p>In addition, there are many cases where C compilers need to issue adiagnostic, but which do not require diagnostic because they are validC++ code. That is kind of obvious, and hence I do not provide examples.</body><!-- Mirrored from c-faq.com/misc/cplusplus.nr.html by HTTrack Website Copier/3.x [XR&CO'2008], Sat, 14 Mar 2009 08:02:55 GMT --></html>⌨️ 快捷键说明
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