No -Wc++-compat warning on uninitialized const field in struct #19297
Comments
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This also happens to global const variable. $: cat s.c |
Quuxplusone
added
clang:diagnostics
Unlike C++, C allows the definition of an uninitialized `const` object. If the object has static or thread storage duration, it is still zero-initialized, otherwise, the object is left uninitialized. In either case, the code is not compatible with C++. This adds a new diagnostic group, `-Wdefault-const-init-unsafe`, which is on by default and diagnoses any definition of a `const` object which remains uninitialized. It also adds another new diagnostic group, `-Wdefault-const-init` (which also enabled the `unsafe` variant) that diagnoses any definition of a `const` object (including ones which are zero-initialized). This diagnostic is off by default. Finally, it adds `-Wdefault-const-init` to `-Wc++-compat`. GCC diagnoses these situations under this flag. Fixes llvm#19297
Unlike C++, C allows the definition of an uninitialized `const` object. If the object has static or thread storage duration, it is still zero-initialized, otherwise, the object is left uninitialized. In either case, the code is not compatible with C++. This adds a new diagnostic group, `-Wdefault-const-init-unsafe`, which is on by default and diagnoses any definition of a `const` object which remains uninitialized. It also adds another new diagnostic group, `-Wdefault-const-init` (which also enabled the `unsafe` variant) that diagnoses any definition of a `const` object (including ones which are zero-initialized). This diagnostic is off by default. Finally, it adds `-Wdefault-const-init` to `-Wc++-compat`. GCC diagnoses these situations under this flag. Fixes llvm#19297
Unlike C++, C allows the definition of an uninitialized `const` object. If the object has static or thread storage duration, it is still zero-initialized, otherwise, the object is left uninitialized. In either case, the code is not compatible with C++. This adds a new diagnostic group, `-Wdefault-const-init-unsafe`, which is on by default and diagnoses any definition of a `const` object which remains uninitialized. It also adds another new diagnostic group, `-Wdefault-const-init` (which also enabled the `unsafe` variant) that diagnoses any definition of a `const` object (including ones which are zero-initialized). This diagnostic is off by default. Finally, it adds `-Wdefault-const-init` to `-Wc++-compat`. GCC diagnoses these situations under this flag. Fixes llvm#19297
Extended Description
At trunk 201801. I am not sure whether clang support the warning flag -Wc++-compat. Currently it does not warn on the uninitialized field in a struct.
$: cat s.c
struct S{const int i;};
void f() {struct S s;}
$: clang-trunk -Wc++-compat -c s.c
$: clang++ -c s.c
clang: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated
s.c:1:8: error: implicit default constructor for 'S' must explicitly initialize the const member 'i'
struct S{const int i;};
^
s.c:1:20: note: declared here
struct S{const int i;};
^
s.c:2:20: note: implicit default constructor for 'S' first required here
void f() {struct S s;}
^
1 error generated.
$:
$: gcc-trunk -Wc++-compat -c s.c
s.c: In function ‘f’:
s.c:2:20: warning: uninitialized const member in ‘struct S’ is invalid in C++ [-Wc++-compat]
void f() {struct S s;}
^
s.c:1:20: note: ‘i’ should be initialized
struct S{const int i;};
^
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