https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105370
Bug ID: 105370
Summary: Improved diagnostics for code from statement
expressions documentation [C++ component]
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: diagnostic, documentation
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: egallager at gcc dot gnu.org
Target Milestone: ---
This is the C++ counterpart to bug 105369. Code is taken from GCC documentation
on Statement Expressions here:
https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs
Testcase:
$ cat stmt_exprsxx.cc
class A
{
public:
int Foo(void);
};
int decay(void)
{
A a;
return ({a;}).Foo();
}
#define X decay
#define macro(a) ({__typeof__(a) b = (a); b + 3; })
template<typename T> T function(T a) { T b = a; return b + 3; }
void foobar()
{
macro(X());
function(X());
}
$
The documentation says that there might be surprising behavior about
temporaries and construction and destruction, which lead the documentation to
the conclusion that "[t]hese considerations mean that it is probably a bad idea
to use statement expressions of this form in header files that are designed to
work with C++." Perhaps there should be some warning about this (current code
doesn't print any warnings with -Wall -Wextra -Weffc++ -pedantic).
