https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65673
Bug ID: 65673 Summary: Compound literal with initializer for zero-sized array drops other initializers Product: gcc Version: 4.9.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: stilor at att dot net I am seeing a strange behavior when a compound initializer is used in a structure initialization. A test case: [[[ struct s { int y; unsigned long *x; }; struct s foo = { .y = 25, .x = (unsigned long [SZ]){}, }; ]]] If SZ is defined to non-zero, the expected output is produced: [[[ /tmp$ gcc -S -o- 1.c -Wall -DSZ=1 .file "1.c" .local __compound_literal.0 .comm __compound_literal.0,8,8 .globl foo .data .align 16 .type foo, @object .size foo, 16 foo: .long 25 .zero 4 .quad __compound_literal.0 .ident "GCC: (Ubuntu 4.9.1-16ubuntu6) 4.9.1" .section .note.GNU-stack,"",@progbits ]]] If SZ is zero, the initializer for .y (".y = 25") member is dropped as well: [[[ /tmp$ gcc -S -o- 1.c -Wall -DSZ=0 .file "1.c" .globl foo .bss .align 16 .type foo, @object .size foo, 16 foo: .zero 16 .ident "GCC: (Ubuntu 4.9.1-16ubuntu6) 4.9.1" .section .note.GNU-stack,"",@progbits ]]] Tested with GCC 4.6.3 and 4.9.1, both exhibit the same behavior. With -Wextra, the code rightfully complains that the initializer for .x is missing - but why the .y initializer is dropped even if there is no initializer for .x? In the mailing list, this was some discussion of this issue: [[[ But in this case, the code attempts to create an unnanmed temporary array of zero elements which, IMO, makes no sense. At the same time, I wouldn't expect gcc to simply omit the initialization for foo.x. I suggest to open a gcc bug for it. ]]] I'd add that this was a reduced test case from a bigger aggregate type - which was an array of such structures. When one of the elements became unused and the size of the bitmap (which was the purpose of the compound literal initializer) was set to zero, the whole array lost its initializers - i.e., even other 'struct s' members of the array, not just the member with a zero-sized array compound literal.