Bug 36750

A related thread: http://gcc.gnu.org/ml/gcc-bugs/1998-07/msg00031.html

I think this is reasonable. Have you tried what clang does in these cases?

But the mail that you link talks about C++ not C...

Author: amonakov
Date: Fri Apr 22 11:53:01 2011
New Revision: 172857

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=172857
Log:
	PR c/36750
	* c-typeck.c (pop_init_level): Do not warn about initializing
	with ` = {0}'.

testsuite:
	* gcc.dg/missing-field-init-2.c: Update testcase.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-typeck.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/missing-field-init-2.c

The above patch suppresses the warning in C regardless of whether the trailing comma is present.  Closing as fixed.

This is still an issue in C++

Nightstrike, is there a particular reason you want C++ warning behavior be adjusted?  Note that unlike C, in C++ you get zero-initialization by default, so you don't need to write ' = {0};' to zero-initialize a structure in the first place.  Thus I don't see if adjusting the warning is desirable for C++.  I might be wrong; in that case I'd recommend you to open a new bug and reference the new bug from here.

Are you sure C++ works like that?  I thought that member variables in a struct would get default initialized to indeterminate values, as seen here:

http://en.cppreference.com/w/cpp/language/default_initialization

Surely, the C++ syntax of saying MyType x = {}; should be supported, as seen here:

http://en.cppreference.com/w/cpp/language/aggregate_initialization

where for instance:

struct S {
    int a;
    float b;
    std::string str;
};

S s = {}; // identical to S s = {0, 0.0, std::string};

That shouldn't warn for the reasons stated in earlier comments.

My statement about zero-initialization was inaccurate (thanks), but the general point still stands: in C you have to write ' = {0}' since empty-braces initializer is not supported by the language (you get a warning with -pedantic); in C++, you can write ' = {}' or 'T foo = T();', but you don't need to write ' = {0}' specifically.

So should I open a new PR for not warning in C++?  Because even the "= {0}" case warns there.

Created attachment 33627 [details]
Test case showing overly strict warning

This still produces false positives in C++11.

I attached a test case with several false positives. The compilation should be clean as there are no uninitialized members. Repros with g++ 4.9.1

Compile with "g++ test.cpp -std=c++11 -Wmissing-field-initializers`"

Produces:

dcsommer@dcsommer-ThinkPad-T440s:~/src/proxygen-oss-test/proxygen$ g++ test.cpp -Wmissing-field-initializers -std=c++11
test.cpp: In function ‘int main()’:
test.cpp:7:10: warning: missing initializer for member ‘Foo::bar’ [-Wmissing-field-initializers]
   Foo f1{};
          ^
test.cpp:7:10: warning: missing initializer for member ‘Foo::baz’ [-Wmissing-field-initializers]
test.cpp:8:11: warning: missing initializer for member ‘Foo::baz’ [-Wmissing-field-initializers]
   Foo f2{0};
           ^
test.cpp:9:14: warning: missing initializer for member ‘Foo::baz’ [-Wmissing-field-initializers]
   Foo f3 = {0};
              ^
test.cpp:10:15: warning: missing initializer for member ‘Foo::baz’ [-Wmissing-field-initializers]
   Foo f4 = {0,};
               ^

(In reply to Daniel Sommermann from comment #11)
> Created attachment 33627 [details]
> Test case showing overly strict warning
> 
> This still produces false positives in C++11.
> 
> I attached a test case with several false positives. The compilation should
> be clean as there are no uninitialized members. Repros with g++ 4.9.1
> 
> Compile with "g++ test.cpp -std=c++11 -Wmissing-field-initializers`"
> 
> Produces:
> 
> dcsommer@dcsommer-ThinkPad-T440s:~/src/proxygen-oss-test/proxygen$ g++
> test.cpp -Wmissing-field-initializers -std=c++11
> test.cpp: In function ‘int main()’:
> test.cpp:7:10: warning: missing initializer for member ‘Foo::bar’
> [-Wmissing-field-initializers]
>    Foo f1{};
>           ^
> test.cpp:7:10: warning: missing initializer for member ‘Foo::baz’
> [-Wmissing-field-initializers]
> test.cpp:8:11: warning: missing initializer for member ‘Foo::baz’
> [-Wmissing-field-initializers]
>    Foo f2{0};
>            ^
> test.cpp:9:14: warning: missing initializer for member ‘Foo::baz’
> [-Wmissing-field-initializers]
>    Foo f3 = {0};
>               ^
> test.cpp:10:15: warning: missing initializer for member ‘Foo::baz’
> [-Wmissing-field-initializers]
>    Foo f4 = {0,};
>                ^


This reproduces with 4.9.2 as well.  Request reopen.

Apparently, this got fixed for C++ somewhere inbetween GCC 4.9.2 and 5.1.1.
```
int main() {
struct S {
    int a;
    float b;
};

S s = {}; // identical to S s = {0, 0.0, std::string};
}
```
Compiled with `-Wextra`, the warning isn't present anymore for GCC 5.1.1.

I think PR 61489 changed the behaviour for GCC 5.