7 ms·

The first sentence: "The C programming language defines a string as char* ." No, it doesn't. A string is by definition "a contiguous sequence of characters te

by _kst_ 8y ago

The first sentence: "The C programming language defines a string as char* ." No, it doesn't. A string is by definition "a contiguous sequence of characters terminated by and including the first null character". A char* value may or may not be a pointer to a string. (Confusing arrays and pointers is perhaps the most common mistake people make when talking about C.)

bergesenha 8y ago
And in C++, the type of a string literal expression is not const char* , but in fact const char (&)[], ie a reference to an array of chars. I was surprised to learn this as I always assigned a literal to a const char* , relying on pointer decay without knowing it.
- _kst_ 8y ago
  In C, the type of a string literal is char[n] where n is the length of the literal plus 1. In C++, it's "array of n const char", or const char[n] It's not of a reference type. See the ISO C++11 standard, 2.4.15 [lex.string]. (In both C and C++, array expressions "decay" to pointer expressions in most contexts. But for example sizeof "hello" is 6 (the size of the string), not the size of a char* pointer.
CodeArtisan 8y ago
A string in C is an implicit type; it's a specialization[1] of an array of characters. Another example of implicit type are Lists in Lisp (specialization of nested pairs). [1] https://en.wikipedia.org/wiki/Specialization_(logic) https://en.wikipedia.org/wiki/Specialization_(logic)
- kazinator 8y ago
  A string in C is entirely built upon convention; it exists in the words of a document only. Common Lisp has a list class that you can specialize a CLOS method on. Also: [1]> (typep nil 'list) T [2]> (typep '(a) 'list) T [3]> (typep 3 'list) NIL And: [4]> (subtypep 'cons 'list) T ; T [5]> (subtypep 'null 'list) T ; T So, kind of apples and oranges.
  - CodeArtisan 8y ago
    I was referring to John McCarthy's definition of a list. IIRC, Common lisp's list type includes both proper and unproper lists. (typep (cons 1 2) 'list) evaluates to true but (length (cons 1 2)) throws a type error (not a list).
- _kst_ 8y ago
  I guess you could think of it as an "implicit type". I prefer to think of it as a data format rather than a data type. (It doesn't satisfy the meaning of "type" as C defines the word.) char[n] (for constant n) is an array type. An object of type char[n] may or may not contain a string.

by _kst_ 8y ago

bergesenha 8y ago

And in C++, the type of a string literal expression is not const char* , but in fact const char (&)[], ie a reference to an array of chars. I was surprised to learn this as I always assigned a literal to a const char* , relying on pointer decay without knowing it.

_kst_ 8y ago
In C, the type of a string literal is char[n] where n is the length of the literal plus 1. In C++, it's "array of n const char", or const char[n] It's not of a reference type. See the ISO C++11 standard, 2.4.15 [lex.string]. (In both C and C++, array expressions "decay" to pointer expressions in most contexts. But for example sizeof "hello" is 6 (the size of the string), not the size of a char* pointer.

CodeArtisan 8y ago

A string in C is an implicit type; it's a specialization[1] of an array of characters. Another example of implicit type are Lists in Lisp (specialization of nested pairs). [1] https://en.wikipedia.org/wiki/Specialization_(logic) https://en.wikipedia.org/wiki/Specialization_(logic)

kazinator 8y ago
A string in C is entirely built upon convention; it exists in the words of a document only. Common Lisp has a list class that you can specialize a CLOS method on. Also: [1]> (typep nil 'list) T [2]> (typep '(a) 'list) T [3]> (typep 3 'list) NIL And: [4]> (subtypep 'cons 'list) T ; T [5]> (subtypep 'null 'list) T ; T So, kind of apples and oranges.
- CodeArtisan 8y ago
  I was referring to John McCarthy's definition of a list. IIRC, Common lisp's list type includes both proper and unproper lists. (typep (cons 1 2) 'list) evaluates to true but (length (cons 1 2)) throws a type error (not a list).
_kst_ 8y ago
I guess you could think of it as an "implicit type". I prefer to think of it as a data format rather than a data type. (It doesn't satisfy the meaning of "type" as C defines the word.) char[n] (for constant n) is an array type. An object of type char[n] may or may not contain a string.