Defining structure variable after structure type

Question

#include 

struct people 
{
    int id;
} person; // that part

int main()
{
    person = {3};   
    std::cout << person.id;

    return 0;
}
         


        

Answer 1

You can't use the structure initialization syntax in a normal assignment, it has to be done when you declare your variable:

struct people 
{
    int id;
} person = { 3 };

If you have a C++11 compatible compiler, you can use the uniform initialization syntax to copy later though:

person = people { 3 };

Answer 2

Once I've seen some keyword after structure, like the "person" here.

It's not a keyword, it's a name. You're allowed to declare variables of a class type in the same statement that defines the type, if you like. It's equivalent to two separate declarations:

struct people 
{
    int id;
};
people person;

However, my code I posted above doesn't compile

It sounds like either your compiler doesn't support C++11 (specifically, assignment from a braced list), or you're compiling with it disabled.

If you can't use C++11, then you'll have to assign each member separately:

// person = {3};   // C++11 only
person.id = 3;

or declare and initialise a local object and assign from that:

people temp = {3};
person = temp;

or initialise it in its declaration, rather than deferring until main:

struct people
{
    int id;
} person = {3};

Answer 3

struct people 
{
    int id;
} person; // that part

person is the global object of type people.

person = {3};

Is incorrect in C++03 and correct in C++11, since {3} will be treated like people{3}