When Should I Use (and Avoid) the `new` Operator in C ?

When to Use and Avoid "new" in C

When instantiating objects in C , it's crucial to understand when to use the "new" operator and when not to. This distinction is particularly important for programmers transitioning from C# or Java.

Avoid "new" for Variables with Defined Scope

If you want an object to exist only within a specific scope, such as a function or loop, you don't need to use "new." Instead, declare the object directly, as in this example:

void foo() {
  Point p = Point(0,0);
} // p is destroyed when foo() exits

Use "new" for Objects with Undefined Lifetime

If you want an object to remain in existence until explicitly deleted, use "new." This is the case for objects with an undetermined lifetime, such as:

• Objects allocated dynamically by a function that needs to return them.
• Objects allocated in memory managed by custom allocators.
• Arrays whose size is determined at runtime.

Example:

Point* p1 = new Point(0, 0); // Allocates p1 on the heap
...
delete p1; // Explicitly deallocates p1 when done

Differences between Variables and Pointers

Using "new" for variables (as in Point* p1 = new Point(0, 0);) can be misleading. It doesn't actually allocate the object on the heap; instead, it allocates a pointer to the object. The object itself remains allocated in-place. This is only visible when creating member variables within classes.

In-Place Allocation for Class Members

Class members are automatically allocated when the class instance is created. This is known as "in-place" allocation. For example:

class Foo {
  Point p;
}; // p is allocated within Foo objects

Performance Considerations

Allocating objects with "new" is more expensive than in-place allocation. It's recommended to minimize its use to optimize performance.

Conclusion

Understanding when to use "new" and when not to is crucial for managing memory effectively in C . By following these guidelines, you can avoid memory leaks and performance issues, ensuring the stability and efficiency of your code.

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