Is an empty initializer list valid C code?

c gcc struct standards initializer
Marcus Ahlberg picture Marcus Ahlberg · Jul 11, 2013 · Viewed 17.3k times · Source

It is common to use {0} to initialize a struct or an array but consider the case when the first field isn't a scalar type. If the first field of struct Person is another struct or array, then this line will result in an error (error: missing braces around initializer).

struct Person person = {0};

At least GCC allows me to use an empty initializer list to accomplish the same thing

struct Person person = {};

But is this valid C code?

Also: Is this line guaranteed to give the same behavior, i.e. a zero-initialized struct?

struct Person person;

Answer

interjay picture interjay · Jul 11, 2013

No, an empty initializer list is not allowed. This can also be shown by GCC when compiling with -std=c99 -pedantic:

a.c:4: warning: ISO C forbids empty initializer braces

The reason is the way the grammar is defined in §6.7.9 of the 2011 ISO C Standard:

initializer:
         assignment-expression
         { initializer-list }
         { initializer-list , }
initializer-list:
         designation(opt) initializer
         initializer-list , designation(opt) initializer

According to that definition, an initializer-list must contain at least one initializer.

Related questions

Anonymous union within struct not in c99?

here is very simplified code of problem I have: enum node_type { t_int, t_double }; struct int_node { int value; }; struct double_node { double value; }; struct node { enum node_type type; union { struct int_node int_n; struct double_…

Read More
Packed bit fields in c structures - GCC

I am working with structs in c on linux. I started using bit fields and the "packed" attribute and I came across a wierd behavior: struct t1 { int a:12; int b:32; int c:4; }__attribute__((packed)); struct t2 { int a:12; int …

Read More
How to remove the warning in gcc 4.6: missing initializer [-Wmissing-field-initializers]?

The code: GValue value = { 0 }; Give the following warning: missing initializer [-Wmissing-field-initializers] I know that's a gcc's BUG; but is there some trick to remove it? really not nice see such unreal warnings. But I don't want power off the warning …

Read More