How Do I Properly Initialize C Struct Members?

Initialization of C Struct Members

In C , members of a struct are not automatically initialized to 0 or any specific value when declared without an initializer list. This means that the values of uninitialized struct members are indeterminate. To ensure that members are initialized to the desired values, you must explicitly initialize them.

Initialization Methods

There are several ways to initialize members of a struct:

1. Initializer List: Using an initializer list in the struct declaration is the simplest way to initialize members. For example:

struct Snapshot {
    double x = 0;
    int y = 0;
};

2. Default Initialization: The default initialization syntax ({}) initializes all members to their default values. In the case of primitive types (such as double and int), this is 0.

Snapshot s = {};

3. Value Initialization: When initializing a struct with an empty initializer list (i.e., {}), value initialization occurs. This initializes each member to its default value or invokes the default constructor if the member is a user-defined type.
4. Constructor with Initialization List: If the struct has a constructor, you can use an initialization list within the constructor to initialize its members.

struct Snapshot {
    int x;
    double y;
    Snapshot(): x(0), y(0) { }
};

5. Assignment Operator: You can also assign values to struct members using the assignment operator (=).

Snapshot s;
s.x = 0;
s.y = 0;

It is important to note that if your struct has user-declared constructors, you cannot use aggregate initialization lists (e.g., {}). In such cases, explicit initialization must be done in the constructors.

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