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I was recently faced with a line of code and four options:
char fullName[30] = {NULL};
A) First element is assigned a NULL character.
B) Every element of the array is assigned 0 ( Zeroes )
C) Every element of the array is assigned NULL
D) The array is empty.
The answer we selected was option C, as, while the array is only initialized with a single NULL, C++ populates the rest of the array with NULL.
However, our professor disagreed, stating that the answer is A, he said:
So the very first element is
NULL, and when you display it, it's displaying the first element, which isNULL.
The quote shows the question in its entirety; there was no other information provided. I'm curious to which one is correct, and if someone could explain why said answer would be correct.
306
You can't initialise a char array with NULL , arrays can never be NULL . You seem to be mixing up pointers and arrays. A pointer could be initialised with NULL . char str[5] = {0};
Array elements are initialized to 0 if they are a numeric type ( int or double ), false if they are of type boolean , or null if they are an object type like String .
the null character is used for the termination of array. it is at the end of the array and shows that the array is end at that point. the array automatically make last character as null character so that the compiler can easily understand that the array is ended.
We can use \u0000 value to create an empty char in Java. The Java compiler uses this value to set as char initial default value. It represents null that shows empty char. See the example below.
To initialise an array of char* to all NULL s: char* array [10] = { NULL }; /* The remaining elements are implicitly NULL. */ char* array [10] = { "/usr/bin/ls", "-l" }; /* Again, remaining elements NULL.
When you initialize an array of characters with a string, the number of characters in the string — including the terminating '\0' — must not exceed the number of elements in the array. Listing the values of all elements you want to initialize, in the order that the compiler assigns the values.
A) First element is assigned a NULL character. D) The array is empty. The answer we selected was option C, as, while the array is only initialized with a single NULL, C++ populates the rest of the array with NULL. However, our professor disagreed, stating that the answer is A, he said:
Since there’s a null byte character guaranteed to be stored at the end of valid characters, then the printf function can be efficiently utilized with the %s format string specifier to output the array’s content. Another useful method to initialize a char array is to assign a string value in the declaration statement.
The question is ill-defined, but Option B seems like the most correct answer.
The result depends on how exactly NULL is defined, which depends on the compiler (more precisely, on the standard library implementation). If it's defined as nullptr, the code will not compile. (I don't think any major implementation does that, but still.)
Assuming NULL is not defined as nullptr, then it must be defined as an integer literal with value 0 (which is 0, or 0L, or something similar), which makes your code equivalent to char fullName[30] = {0};.
This fills the array with zeroes, so Option B is the right answer.
In general, when you initialize an array with a brace-enclosed list, every element is initialized with something. If you provide fewer initializers than the number of elements, the remaining elements are zeroed.
Regarding the remaining options:
Option C is unclear, because if the code compiles, then NULL is equivalent to 0, so option C can be considered equivalent to Option B.
Option A can be valid depending on how you interpret it. If it means than the remaining elements are uninitialized, then it's wrong. If it doesn't specify what happens to the remaining elements, then it's a valid answer.
Option D is outright wrong, because arrays can't be "empty".
116
char fullName[30] = {NULL};
This is something that should never be written.
NULL is a macro that expands to a null pointer constant. A character - not a pointer - is being initialised here, so it makes no sense to use NULL.
It just so happens that some null pointer constants are also integer literals with value 0 (i.e. 0 or 0L for example), and if NULL expands to such literal, then the shown program is technically well-formed despite the abuse of NULL. What the macro expands to exactly is defined by the language implementation.
If NULLinstead expands to a null pointer constant that is not an integer literal such as nullptr - which is entirely possible - then the program is ill-formed.
NULL shouldn't be written in C++ at all, even to initialise pointers. It exists for backwards compatibility with C to make it easier to port C programs to C++.
Now, let us assume that NULL happens to expand to an integer literal on this particular implementation of C++.
Nothing in the example is assigned. Assignment is something that is done to pre-existing object. Here, and array is being initialised.
The first element of the array is initialised with the zero literal. The rest of the elements are value initialised. Both result in the null character. As such, the entire array will be filled with null characters.
A simple and correct way to write the same is:
char fullName[30] = {};
B and C are equally close to being correct, except for wording regarding "assignment". They fail to mention value initialisation, but at least the outcome is the same. A is not wrong either, although it is not as complete because it fails to describe how the rest of the elements are initialised.
If "empty" is interpreted as "contains no elements", then D is incorrect because the array contains 30 elements. If it is interpreted as "contains the empty string", then D would be a correct answer.
22
You are almost correct.
The professor is incorrect. It is true that display finishes at the first NULL (when some approaches are used), but that says nothing about the values of the remainder of the array, which could be trivially examined regardless.
[dcl.init/17.5]:: [..] the ith array element is copy-initialized with xi for each 1 ≤ i ≤ k, and value-initialized for each k < i ≤ n. [..]
However, none of the options is strictly correct and well-worded.
What happens is that NULL is used to initialise the first element, and the other elements are zero-initialised. The end result is effectively Option B.
Thing is, if NULL were defined as an expression of type std::nullptr_t on your platform (which it isn't, but it is permitted to be), the example won't even compile!
NULL is a pointer, not a number. Historically it has been possible to mix and match the two things to some degree, but C++ has tried to tighten that up in recent years, and you should avoid blurring the line.
A better approach is:
char fullName[30] = {};
And the best approach is:
std::string fullName;
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