CODEWITHSUNDEEP
cc99designated-initializer
Josh Petitt
Josh Petitt

Reputation: 9579

C struct initialization with C99 - Is mixing named and unnamed members valid?

Given the following:

struct example_struct
{
  char c;
  int i;
};

Is any the following initializer syntax valid in C99?

Syntax example #1

struct example_struct example = { 'a', .i = 1};

Syntax example #2

struct example_struct example = { .c = 'a', 1};

I am writing a simple struct parser and in my testing, this does not cause a compiler error using XCode 4.2. I would like my parser to be C99 compliant. My understanding (without a standard reference) is that a struct initializer should either have all unnamed or named (i.e. designated) members.

Should syntax example #1 and #2 be compiler errors?

If the examples are valid, what are the rules for the initialization syntax?

UPDATED QUESTION EXAMPLES

struct example_struct_3
{
  char c;
  int i;
  float f;
};

struct example_struct_3 example = { .i = 1, 1.0};

In the same main question, how would example three work? I'm mainly confused about the arbitrary ordering of designated initializers with standard initializers.

Upvotes: 5

Views: 1739

Answers (1)

ouah
ouah

Reputation: 145859

Both your initializations example 1 and 2 are valid C99/C11 initializations. You can mix designation initializers and non-designation initializers in an initializer list.

EDIT: regarding your new example 3, the initialization is also valid. After initialization, example.c has value 0, example.i has value 1 and example.f has value (float) 1.0.

Upvotes: 7

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