In C++, function pointers can be converted into function objects through the std::function template: use std::function to wrap function pointers into function objects. Use the std::function::target member function to convert a function object to a function pointer. This transformation is useful in scenarios such as event handling, function callbacks, and generic algorithms, providing greater flexibility and code reusability.

In C++, a closure is a lambda expression that can access external variables. To create a closure, capture the outer variable in the lambda expression. Closures provide advantages such as reusability, information hiding, and delayed evaluation. They are useful in real-world situations such as event handlers, where the closure can still access the outer variables even if they are destroyed.

Symbols, including functions, variables, and classes, are exported in C++ through the extern "C" keyword. Exported symbols are extracted and used according to C language rules between compilation units or when interacting with other languages.

Can. C++ allows nested function definitions and calls. External functions can define built-in functions, and internal functions can be called directly within the scope. Nested functions enhance encapsulation, reusability, and scope control. However, internal functions cannot directly access local variables of external functions, and the return value type must be consistent with the external function declaration. Internal functions cannot be self-recursive.

Implementing a custom comparator can be accomplished by creating a class that overloads operator(), which accepts two parameters and indicates the result of the comparison. For example, the StringLengthComparator class sorts strings by comparing their lengths: Create a class and overload operator(), returning a Boolean value indicating the comparison result. Using custom comparators for sorting in container algorithms. Custom comparators allow us to sort or compare data based on custom criteria, even if we need to use custom comparison criteria.

C++ lambda expressions bring advantages to functional programming, including: Simplicity: Anonymous inline functions improve code readability. Code reuse: Lambda expressions can be passed or stored to facilitate code reuse. Encapsulation: Provides a way to encapsulate a piece of code without creating a separate function. Practical case: filtering odd numbers in the list. Calculate the sum of elements in a list. Lambda expressions achieve the simplicity, reusability, and encapsulation of functional programming.

The methods for handling C++STL hash conflicts are: chain address method: using linked lists to store conflicting elements, which has good applicability. Open addressing method: Find available locations in the bucket to store elements. The sub-methods are: Linear detection: Find the next available location in sequence. Quadratic Detection: Search by skipping positions in quadratic form.

Best practice for access modifiers for Java functions: Use the most restrictive modifier, which is set to private by default. Inner classes use the private modifier. Protected methods use the protected modifier to allow access by subclasses. All properties in the immutable class are set to private and accessed through getter methods. Public APIs use the public modifier so that they can be accessed by external classes.