Final answer:
In many programming languages, when instantiating a struct, all fields must be initialized before the object can be used to ensure well-defined values and prevent unpredictable behavior.
Step-by-step explanation:
When you instantiate a struct in many programming languages, it is indeed required that all fields are initialized before the object can be used. This ensures that each field has a well-defined value and that the program can rely on each struct field having been explicitly set to a value. In languages like C and C++, a struct can be partially initialized, but the uninitialized fields will typically contain garbage data. Designed to be a collection of variables grouped together, initializing a struct prevents unpredictable behavior caused by this uninitialized data. However, some modern languages, like Swift, enforce rules where all properties of a struct must be initialized before an instance of that struct can be used unless you are using specific language features that allow otherwise (such as optionals or explicit initialization methods).