Can C Allocate an Empty Array, and If So, Is It Safe to Use?

C 's Memory Allocation: Can You Allocate an Empty Array?

In C , memory allocation for arrays can be done dynamically using the new operator. However, what happens when you allocate an array of size zero?

cout << new int[0] << endl;

Will this allocate memory for an empty block? Let's explore the standard's standpoint.

Standard Interpretation

According to the C standard (5.3.4/7), "When the value of the expression in a direct-new-declarator is zero, the allocation function is called to allocate an array with no elements."

Dereferencing Concerns

However, the standard (3.7.3.1/2) explicitly states that "The effect of dereferencing a pointer returned as a request for zero size is undefined." This means that while it is technically possible to allocate an empty array, attempting to access its elements (e.g., by dereferencing the returned pointer) is undefined behavior.

Additional Notes

Even though the standard permits the allocation of empty arrays, it emphasizes that requests for zero-sized memory can still fail. This is because dynamic memory allocation may rely on external system libraries (such as malloc()) which may have their own handling of such requests.

Implications and Best Practices

In practice, it is generally considered good practice to avoid allocating empty arrays. The behavior is undefined, and it may lead to unexpected results across different platforms and environments. If you need to handle scenarios where an empty container is necessary, consider using alternative approaches such as using a std::vector or std::array with a size of zero.

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