Defined in alloca.h, this function allocates local storage in a function. It returns a pointer to size bytes of memory. The default implementation returns an eight-byte aligned block of memory on the stack.

Memory returned from alloca() must never be passed to free(). Instead, the memory is de-allocated automatically when the function that called alloca() returns.

This function is a common nonstandard extension to many C libraries.

void *alloca(size_t size);