c++ explicit keyword for function without arguments
Possible Duplicate:
What does the explicit keyword in C++ mean?
Is there a reason to use the explicit keyword for a function that doesn't take any arguments? Does it have any effect? I'm wondering because I just came across the line
explicit char_separator()
near the end of the page documenting boost::char_separator ( http://www.boost.org/doc/libs/1_47_0/libs/tokenizer/char_separator.htm ), but it's not explained any further there.
Reading explanation of members :
explicit char_separator(const Char* dropped_delims,
const Char* kept_delims = "",
empty_token_policy empty_tokens = drop_empty_tokens)
explicit char_separator()
The explicit keyword for the 1st constructor requires explicit creation of objects of char_separator type. What does the explicit keyword mean in C++? covers the explicit keyword very well.
The explicit keyword for the 2nd constructor is a noise and is ignored.
EDIT
From the c++ standard :
7.1.2 p6 tells :
The explicit specifier shall be used only in declarations of constructors within a class declaration; see 12.3.1.
12.3.1 p2 tells :
An explicit constructor constructs objects just like non-explicit constructors, but does so only where direct-initialization syntax (8.5) or where casts (5.2.9, 5.4) are explicitly used. A default constructor may be an explicit constructor; such a constructor will be used to perform default-initialization or value-initialization (8.5). [Example:
class Z {
public:
explicit Z();
explicit Z(int);
// ...
};
Z a; // OK: default-initialization performed
Z a1 = 1; // error: no implicit conversion
Z a3 = Z(1); // OK: direct initialization syntax used
Z a2(1); // OK: direct initialization syntax used
Z* p = new Z(1); // OK: direct initialization syntax used
Z a4 = (Z)1; // OK: explicit cast used
Z a5 = static_cast<Z>(1); // OK: explicit cast used
—end example]
So, the default constructor with the explicit keyword is the same as without this keyword.
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