[Bug c/56647] New: use return value of malloc() as initializer

[Bug c/56647] New: use return value of malloc() as initializer

[zhabgyuan1993 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56647

             Bug #: 56647
           Summary: use return value of  malloc() as initializer
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zhabgyuan1993@gmail.com


Created attachment 29687
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29687
the preprocessed file for r.c

$:cat r.c
------------------------------------------------------
#include<stdio.h>
#include<stdlib.h>
int *c;
c = (int *)malloc(sizeof(int));
int main(void)
{
return 0;
}

error or warning
-------------------------------------------------------
r.c:4:1: warning: data definition has no type or storage class [enabled by
default]
r.c:4:1: error: conflicting types for ‘c’
r.c:3:6: note: previous declaration of ‘c’ was here
r.c:4:5: warning: initialization makes integer from pointer without a cast
[enabled by default]
r.c:4:1: error: initializer element is not constant


$: gcc -v -save-temps r.c
-------------------------------------------------------
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.7/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.7.2-2ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs
--enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.7 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.7.2 (Ubuntu/Linaro 4.7.2-2ubuntu1) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/4.7/cc1 -E -quiet -v -imultiarch
x86_64-linux-gnu r.c -mtune=generic -march=x86-64 -fpch-preprocess
-fstack-protector -o r.i
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-linux-gnu/4.7/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/4.7/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/4.7/cc1 -fpreprocessed r.i -quiet -dumpbase r.c
-mtune=generic -march=x86-64 -auxbase r -version -fstack-protector -o r.s
GNU C (Ubuntu/Linaro 4.7.2-2ubuntu1) version 4.7.2 (x86_64-linux-gnu)
    compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C (Ubuntu/Linaro 4.7.2-2ubuntu1) version 4.7.2 (x86_64-linux-gnu)
    compiled by GNU C version 4.7.2, GMP version 5.0.2, MPFR version 3.1.0-p3,
MPC version 0.9
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: efa32fef7aa241fa03ac6d7ad2a4a2cf
r.c:4:1: warning: data definition has no type or storage class [enabled by
default]
r.c:4:1: error: conflicting types for ‘c’
r.c:3:6: note: previous declaration of ‘c’ was here
r.c:4:5: warning: initialization makes integer from pointer without a cast
[enabled by default]
r.c:4:1: error: initializer element is not constant

[Bug c/56647] use return value of malloc() as initializer

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56647

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-03-18 05:48:41 UTC ---
The diagnostic seems correct for me.

[Bug c/56647] use return value of malloc() as initializer

[zhabgyuan1993 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56647

--- Comment #2 from shia <zhabgyuan1993 at gmail dot com> 2013-03-18 05:54:54 UTC ---
I think maybe only this one is right:
r.c:4:1: error: initializer element is not constant
the other part may cause little confused.

[Bug c/56647] use return value of malloc() as initializer

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56647

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-03-18 06:11:55 UTC ---
(In reply to comment #0)
> -------------------------------------------------------
> r.c:4:1: warning: data definition has no type or storage class [enabled by
> default]
> r.c:4:1: error: conflicting types for ‘c’
> r.c:3:6: note: previous declaration of ‘c’ was here
> r.c:4:5: warning: initialization makes integer from pointer without a cast
> [enabled by default]
> r.c:4:1: error: initializer element is not constant
> 


Since this is at the top level, only definitions are allowed which is what GCC
is assuming.  GCC has an extension of not needing a type or storage class for
some variable and assume int as the type.  That comes to the second error
message of the conflicting types.
The next warning is due to the int of c now being int from the extension.
And the last error message is saying the initializer element is not constant as
this is the top level.

That explains exactly what is going on and why GCC's warnings/error messages
are correct.
The trunk gives:
t1.c:4:1: warning: data definition has no type or storage class [enabled by
default]
 c = (int *)malloc(sizeof(int));
 ^
t1.c:4:1: error: conflicting types for ‘c’
t1.c:3:6: note: previous declaration of ‘c’ was here
 int *c;
      ^
t1.c:4:5: warning: initialization makes integer from pointer without a cast
[enabled by default]
 c = (int *)malloc(sizeof(int));
     ^
t1.c:4:1: error: initializer element is not constant
 c = (int *)malloc(sizeof(int));
 ^

Which should better explain what is going on here.

[Bug c/56647] use return value of malloc() as initializer

[zhabgyuan1993 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56647

shia <zhabgyuan1993 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED

--- Comment #4 from shia <zhabgyuan1993 at gmail dot com> 2013-03-18 06:34:54 UTC ---
Thank you.It's clear after your clarifying patiently

[Bug c/56647] use return value of malloc() as initializer

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56647

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|FIXED                       |INVALID

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-18 09:38:41 UTC ---
.