2013-07-08 10:46, Reece Dunn skrev:
On 8 July 2013 08:49, Murray Cumming <[email protected]
<mailto:[email protected]>> wrote:
It would be nice to have some general fix for this warning when using
--std=c++11 with g++:
optiongroup.cc: In member function 'void
Glib::OptionGroup::add_entry(const Glib::OptionEntry&)':
optiongroup.cc:320:3: error: missing initializer for member
'_GOptionEntry::short_name' [-Werror=missing-field-initializers]
optiongroup.cc:320:3: error: missing initializer for member
'_GOptionEntry::flags' [-Werror=missing-field-initializers]
optiongroup.cc:320:3: error: missing initializer for member
'_GOptionEntry::arg' [-Werror=missing-field-initializers]
optiongroup.cc:320:3: error: missing initializer for member
'_GOptionEntry::arg_data' [-Werror=missing-field-initializers]
optiongroup.cc:320:3: error: missing initializer for member
'_GOptionEntry::description' [-Werror=missing-field-initializers]
optiongroup.cc:320:3: error: missing initializer for member
'_GOptionEntry::arg_description' [-Werror=missing-field-initializers]
It's caused by the GLIBMM_INITIALIZE_STRUCT macro definition using the
second possibility rather than the first, because __STRICT_ANSI__
is not
defined, but I don't know why that would have been defined before, but
not with C++11.
https://git.gnome.org/browse/glibmm/tree/glib/glibmm/utility.h#n28
I found
http://stackoverflow.com/questions/5580921/how-can-i-make-c0x-and-strict-ansi-get-along.
It looks like -- from this and other websites -- that gcc defines
__STRICT_ANSI__ if --std=c++11 is defined.
With:
$ g++ --version
g++ (Debian 4.7.3-4) 4.7.3
and:
$ touch empty.c
$ touch empty.cpp
I get:
$ gcc -std=c99 -E -dM empty.c | grep -P "(__STRICT|__cplusplus)"
#define __STRICT_ANSI__ 1
$ gcc -std=gnu99 -E -dM empty.c | grep -P "(__STRICT|__cplusplus)"
$ gcc -std=c++98 -E -dM empty.cpp | grep -P "(__STRICT|__cplusplus)"
#define __STRICT_ANSI__ 1
#define __cplusplus 199711L
$ gcc -std=gnu++98 -E -dM empty.cpp | grep -P "(__STRICT|__cplusplus)"
#define __cplusplus 199711L
$ gcc -std=c++11 -E -dM empty.cpp | grep -P "(__STRICT|__cplusplus)"
#define __STRICT_ANSI__ 1
#define __cplusplus 201103L
$ gcc -std=gnu++11 -E -dM empty.cpp | grep -P "(__STRICT|__cplusplus)"
#define __cplusplus 201103L
$ gcc -std=c++0x -E -dM empty.cpp | grep -P "(__STRICT|__cplusplus)"
#define __STRICT_ANSI__ 1
#define __cplusplus 201103L
$ gcc-4.4 -std=c++0x -E -dM empty.cpp | grep -P
"(__STRICT|__cplusplus)"
#define __STRICT_ANSI__ 1
#define __cplusplus 1
So:
__STRICT_ANSI__ checks for ISO/ANSI compliance vs GNU extensions (C or
C++).
__cplusplus checks for C++ vs C (with 199711L for C++98, 1 for C++0x
(pre-standardisation) and 201103L for C++11).
HTH,
- Reece
Some info copied from the description of gcc 4.7.0:
-Wmissing-field-initializers
This warning is included in '-Wextra'. To get other '-Wextra'
warnings without
this one, use '-Wextra -Wno-missing-field-initializers'.
GCC normally defines __STDC__ to be 1, and in addition defines
__STRICT_ANSI__ if
you specify the '-ansi' option, or a '-std' option for strict
conformance to some version
of ISO C.
-----------------
GLIBMM_INITIALIZE_STRUCT chooses the second alternative when
__STRICT_ANSI__ *is* defined.
More tests with gcc:
$ gcc-4.7 -E -dM empty.cpp | grep STRICT
$ gcc-4.7 -std=c++11 -E -dM empty.cpp | grep STRICT
#define __STRICT_ANSI__ 1
$ gcc-4.7 -pedantic -Wextra -E -dM empty.cpp | grep STRICT
$ gcc-4.7 -pedantic -Wextra -std=c++11 -E -dM empty.cpp | grep STRICT
#define __STRICT_ANSI__ 1
$ gcc-4.7 -pedantic -Wextra -std=gnu++11 -E -dM empty.cpp | grep STRICT
When no -std option is given, __STRICT_ANSI__ is not defined, and
GLIBMM_INITIALIZE_STRUCT
chooses the first alternative. The default value is -std=gnu++98.
Solution? Why not use std::memset() in GLIBMM_INITIALIZE_STRUCT?
Probable answer: Because it requires #include <cstring>.
The glib macros G_GNUC_BEGIN_IGNORE_DEPRECATIONS and
G_GNUC_END_IGNORE_DEPRECATIONS contain a trick that temporarily
suppresses a particular warning.
#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
#define G_GNUC_BEGIN_IGNORE_DEPRECATIONS \
_Pragma ("GCC diagnostic push") \
_Pragma ("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
#define G_GNUC_END_IGNORE_DEPRECATIONS \
_Pragma ("GCC diagnostic pop")
#else
#define G_GNUC_BEGIN_IGNORE_DEPRECATIONS
#define G_GNUC_END_IGNORE_DEPRECATIONS
#endif
I don't know exactly what kind of preprocessor directive _Pragma is. It
might be useful in GLIBMM_INITIALIZE_STRUCT.
Do we really need GLIBMM_INITIALIZE_STRUCT? There are 3 uses in glibmm
and 6 in gtkmm. They can easily be replaced by std::memset().
Kjell
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