如何一次初始化几个struct变量？

Question

For a struct like

struct data{
   int a;
   int b;
   int c;
};

how can I initialize several instances of that struct with identical values at once?

Instead of:

struct data object1 = {0,0,0}, object2 = {0,0,0}, object3 = {0,0,0};

Answer 1

You can take an array of the struct s and use a single brace-enclosed initializer, like

 struct data object [3] = {0};

go have multiple variables of that structure type, all initialized to 0 (or equivalent).

This makes use of a special property of initialization, quoting C11 , chapter

The initialization shall occur in initializer list order, each initializer provided for a particular subobject overriding any previously listed initializer for the same subobject; ¹⁵¹⁾ all subobjects that are not initialized explicitly shall be initialized implicitly the same as objects that have static storage duration.

and, initialization for objects having static storage,

[...] If an object that has static or thread storage duration is not initialized explicitly, then:

— if it has pointer type, it is initialized to a null pointer;

— if it has arithmetic type, it is initialized to (positive or unsigned) zero;

— if it is an aggregate, every member is initialized (recursively) according to these rules, and any padding is initialized to zero bits;

— if it is a union, the first named member is initialized (recursively) according to these rules, and any padding is initialized to zero bits;

That said, in case you don't want all the values to be initialized to 0 , there are alternate ways. As mentioned in the other answer by Mr. Jonathon Reinhart, you can make use of designated initializers.

Answer 2

First off, I tend to favor the Linux kernel style and strongly prefer designated initializers .

I would do what they do, and create a macro for initializing your struct. That makes it easy to add elements and control how they are initialized.

struct data {
   int a;
   int b;
   int c;
};

#define INIT_DATA { \
    .a = 0, \
    .b = 0, \
    .c = 0, \
}

And use it like this:

struct data mydata = INIT_DATA;

Continuing with the Linux style, you wouldn't have more than one of these variables on a line anyway. It makes different easier to look at when variables are added/removed. What is wrong with:

struct data old_data = INIT_DATA;
struct data new_data = INIT_DATA;

If you have more than a couple, should they be individual variables or should they be an array? If so, you can take advantage of a GNU extension to initialize a range:

struct data datas[N] = {
    [0 ... N-1] = INIT_DATA,
};

Otherwise, you will need to use a regular old loop to initialize your data at run-time.

Answer 3

how can I initialize several instances of that struct with identical values at once?

Not really " at once ", whatever this is meant to mean, but at least without repeating yourself (that is following the DRY-principal ) you could do:

int main(void)
{
  struct data object1 = {1, 2, 3}, object2 = object1, object3 = object1;

  ...
}

or with each definition on a separate line:

int main(void)
{
  struct data object1 = {1, 2, 3};
  struct data object2 = object1;
  struct data object3 = object1;

  ...
}

Answer 4

Create an array of structures and initialize them in a loop.

struct data array[N_ITEMS];

for(i=0; i<N_ITEMS; i++)
{
    array[i].a=a;
    array[i].b=b;
    array[i].c=c;
}

If you want to initialize all fields to 0, you can use memset:

 memset(array, 0, sizeof(array));