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Initializers

So now you're probably wondering: "Hey TJ, so... how do we actually make an instance of a struct"? You may have noticed in the previous lesson all we did was define the struct type.

Unfortunately, there are a few different ways to initialize a struct, I'll give you an example of each using this struct:

struct City {
  char *name;
  int lat;
  int lon;
};

Zero Initializer

int main() {
  struct City c = {0};
}

This sets all the fields to 0 values.

Positional Initializer

int main() {
  struct City c = {"San Francisco", 37, -122};
}

Designated Initializer

This is my (generally) preferred way to initialize a struct. Why?

It's easier to read (has the field names)
If the fields change, you don't have to worry about breaking the ordering

int main() {
  struct City c = {
    .name = "San Francisco",
    .lat = 37,
    .lon = -122
  };
}

Remember, it's .name not name. If this trips you up, just remember it's .name and not name because that's how you access the field, e.g. c.name.

Accessing Fields

Accessing a field in a struct is done using the . operator. For example:

struct City c;
c.lat = 41; // Set the latitude
printf("Latitude: %d", c.lat); // Print the latitude

There's another way to do this for pointers that we'll get to later.

Assignment

Complete the new_coord function. It accepts 3 integers and returns a Coordinate.

Use the "designated initializer" syntax... because I said so.

Tip

The easiest way to return a struct is to initialize it in a variable first. If you want to skip the variable assignment, you can write something like this:

struct City new_city(char *name, int lat, int lon) {
    return (struct City){.name = name, .lat = lat, .lon = lon};
}