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This might look like a smart way to assign the return value of malloc to ptr and check if it is NULL in one step, but the malloc call and the assignment to ptr is a side effect of evaluating the expression that forms the assert condition.
In computer programming, lazy initialization is the tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.
A null pointer has a value reserved for indicating that the pointer does not refer to a valid object. Null pointers are routinely used to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.
Another frequent source of dangling pointers is a jumbled combination of malloc() and free() library calls: a pointer becomes dangling when the block of memory it points to is freed. As with the previous example one way to avoid this is to make sure to reset the pointer to null after freeing its reference—as demonstrated below.
For example, the standard way to allocate memory on the heap is to invoke a memory allocation function, such as malloc, with an argument indicating how many bytes are required. The function returns an untyped pointer (type void * ), which the calling code must explicitly or implicitly cast to the appropriate pointer type.
Used in FreeBSD's PHK malloc(3) for debugging when /etc/malloc.conf is symlinked to "-J" to initialize all newly allocated memory as this value is not a NULL pointer or ASCII NUL character. ABABABAB: Used by Microsoft's debug HeapAlloc() to mark "no man's land" guard bytes after allocated heap memory. [26] ABADBABE
For example, the padding to add to offset 0x59d for a 4-byte aligned structure is 3. The structure will then start at 0x5a0, which is a multiple of 4. However, when the alignment of offset is already equal to that of align, the second modulo in (align - (offset mod align)) mod align will return zero, therefore the original value is left unchanged.
In C, the library function malloc is used to allocate a block of memory on the heap. The program accesses this block of memory via a pointer that malloc returns. When the memory is no longer needed, the pointer is passed to free which deallocates the memory so that it can be used for other purposes.