Can You Determine the Size of an Array Allocated with `new` in C ?

Determining Array Size Allocated with new

Can you obtain the size of an array allocated with new T[]?

This question explores the challenge of programmatically determining the size of a C array allocated on the heap using the new operator.

Why is this Challenging?

Unlike arrays declared on the stack (int arr[256];), which have a fixed size known during compilation, arrays allocated with new have their size determined dynamically at runtime. This means that the compiler cannot know the size of such arrays during compilation, and the sizeof operator only returns the size of the pointer itself.

Compiler Limitations

sizeof is evaluated statically by the compiler, meaning it cannot be used for dynamically allocated arrays. Additionally, C arrays are not first-class objects and decay into pointers, making it difficult for the compiler or program to distinguish between pointers to the start of an allocated array and pointers to single objects or arbitrary memory locations.

Runtime Knowledge

delete [] knows the allocated size, but this knowledge resides in the runtime or operating system's memory manager and is not accessible during compilation.

Memory Management Considerations

C and C leave memory management to the programmer and operating system. As a result, implementing new and delete is platform-dependent and may not involve keeping track of allocated array sizes. This approach allows for efficient and flexible memory management on various systems, but it sacrifices the ability to programmatically obtain array sizes.

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