Initializing array of structures

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

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It s a designated initializer  introduced with the C99 standard  it allows you to initialize specific members of a struct or union object by name   my data is obviously a typedef for a struct type that has a member name of type char   or char  N

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There s no  step-by-step  here  When initialization is performed with constant expressions  the process is essentially performed at compile time  Of course  if the array is declared as a local object  it is allocated locally and initialized at run-time  but that can be still thought of as a single-step process that cannot be meaningfully subdivided   Designated initializers allow you to supply an initializer for a specific member of struct object  or a specific element of an array   All other members get zero-initialized  So  if my data is declared as  typedef struct my data     int a    const char  name    double x    my data    then your  my data data            name    Peter            name    James            name    John            name    Mike         is simply a more compact form of   my data data 4          0   Peter   0          0   James   0          0   John   0          0   Mike   0        I hope you know what the latter does

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There are only two syntaxes at play here    Plain old array initialisation   int x      0  0      x 0    0  x 1    0  A designated initialiser  See the accepted answer to this question  How to initialize a struct in accordance with C programming language standards  The syntax is pretty self-explanatory though  You can initialise like this   struct X       int a      int b    struct X foo     0  1       a   0  b   1   or to use any ordering   struct X foo      b   0   a   1       a   1  b   0

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It s called designated initializer which is introduced in C99  It s used to initialize struct or arrays  in this example  struct   Given  struct point        int x  y       the following initialization  struct point p      y   2   x   1      is equivalent to the C89-style  struct point p     1  2

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This is quite simple  my data is a before defined structure type  So you want to declare an my data-array of some elements  as you would do with   char a        a    b    c    d       So the array would have 4 elements and you initialise them as   a 0     a   a 1     b   a 1     c   a 1    d     This is called a designated initializer  as i remember right    and it just indicates that data has to be of type my dat and has to be an array that needs to store so many my data structures that there is a structure with each type member name Peter  James  John and  Mike

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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    quot Peter quot            name    quot James quot            name    quot John quot            name    quot Mike quot        as  my data data            0       name    quot Peter quot          1       name    quot James quot          2       name    quot John quot          3       name    quot Mike quot         or  my data data            0  name    quot Peter quot        1  name    quot James quot        2  name    quot John quot        3  name    quot Mike quot       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    quot Mike quot        1  name    quot James quot        0  name    quot Peter quot        2  name    quot John quot       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    quot Mike quot        2  age   40       1  name    quot James quot        3  age   23       0  name    quot Peter quot        2  name    quot John quot       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

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