Initializing array of structures [duplicate]

Question

Here's initialization I just found in somebody else's question.

my_data data[]={     { .name = "Peter" },     { .name = "James" },     { .name = "John" },     { .name = "Mike" } }; 

I never saw something like this before and can't find explanation how is .name possible to be correct.
What I'm looking for is how step by step this process goes.

It looks like it gets:

1. data;
2. *data;
3. (*data).name;
4. (*data).name="Peter";

Or am I totally wrong?

Answer 1

my_data is a struct with name as a field and data[] is arry of structs, you are initializing each index. read following:

5.20 Designated Initializers:

In a structure initializer, specify the name of a field to initialize with .fieldname =' before the element value. For example, given the following structure,

struct point { int x, y; }; 

the following initialization

struct point p = { .y = yvalue, .x = xvalue }; 

is equivalent to

struct point p = { xvalue, yvalue }; 

Another syntax which has the same meaning, obsolete since GCC 2.5, is fieldname:', as shown here:

struct point p = { y: yvalue, x: xvalue }; 

You can also write:

my_data data[] = {     { .name = "Peter" },     { .name = "James" },     { .name = "John" },     { .name = "Mike" } }; 

as:

my_data data[] = {     [0] = { .name = "Peter" },     [1] = { .name = "James" },     [2] = { .name = "John" },     [3] = { .name = "Mike" } };  

or:

my_data data[] = {     [0].name = "Peter",     [1].name = "James",     [2].name = "John",     [3].name = "Mike" };  

Second and third forms may be convenient as you don't need to write in order for example all of the above example are equivalent to:

my_data data[] = {     [3].name = "Mike",     [1].name = "James",     [0].name = "Peter",     [2].name = "John" };  

If you have multiple fields in your struct (for example, an int age), you can initialize all of them at once using the following:

my_data data[] = {     [3].name = "Mike",     [2].age = 40,     [1].name = "James",     [3].age = 23,     [0].name = "Peter",     [2].name = "John" };  

To understand array initialization read Strange initializer expression?

Additionally, you may also like to read @Shafik Yaghmour's answer for switch case: What is “…” in switch-case in C code