How are null-terminated strings terminated in C++11?

Question

Maybe it's stupid or obvious but I couldn't google any answer. What character ends a null-terminated string in C++11? NULL (which is in fact 0) or new nullptr? On the one hand, nullptr is supposed to replace NULL. On the other, though, I'm not sure if nullptr is a character at all. Or can be interpreted as one.

Answer 1

NULL and nullptr has little to do with null-terminated strings. Both NULL and nullptr are used to denote a pointer which points to nothing, ie. null.

The null-termination of c-style strings is still (and has always) been denoted by a CharT having the integral value 0; or as it's most often written when talking, through a char-literal; '\0'.

Remember that character types are nothing more than integral types with some special meaning.

Comparing a char to an int (which is the type of literal 0) is allowed, it's also allowed to assign the value 0 to a char, as stated: a character type is an integral type.. and integral types hold integral values.

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Why this confusion?

Back in the days when we didn't have nullptr, instead we had the macro NULL to denote that a certain pointer didn't have anything to point towards. The value of NULL is, and was, implementation-specific but the behaviour was well-defined; it shall not compare equal to any pointer value that is actually pointing to something.

As a result of how the behaviour of NULL was described plenty of compilers used #define NULL 0, or similar construct, resulting in a "feature" where one could easily compare NULL to any integral type (including char) to see if it's relation to the value zero.

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With the previously stated in mind you'd often stumbled upon code such as the below, where the for-condition would be equivalent of having *ptr != 0.

char const * str = "hello world";

for (char const * ptr = str; *ptr != NULL; ++ptr) {
  ...    
}

^{Lesson learned: Just because something works doesn't mean that it is correct...}

Answer 2

NULL and nullptr are completely separate concepts from the "null terminator". They have nothing more in common than the word "null". The null terminator is a character with value 0. It has nothing to do with null pointers.

You can use 0 or '\0' etc.