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Section: 22.9.2.2 [bitset.cons] Status: C++11 Submitter: Christopher Jefferson Opened: 2010-03-07 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
As mentioned on the boost mailing list:
The following code, valid in C++03, is broken in C++0x due to ambiguity between the "unsigned long long" and "char*" constructors.
#include <bitset> std::bitset<10> b(0);
[ The proposed resolution has been reviewed by Stephan T. Lavavej. ]
[ Post-Rapperswil ]
The proposed resolution has two problems:
it fails to provide support for non-terminated strings, which could be easily added and constitutes an important use-case. For example, the following code would invoke UB with the current P/R:
because it requires the evaluation (under the as-if rule, to be fair, but it doesn't matter) of basic_string<char>(s)char s[4] = { '0', '1', '0', '1' }; // notice: not null-terminated! bitset<4> b(s, 0, 4);
it promotes a consistency between the two bitset constructors that take a const std::string& and a const char*, respectively, while practice established by std::basic_string would recommend a different set of parameters. In particular, the constructor of std::basic_string that takes a const char* does not have a pos parameter
Moved to Tentatively Ready with revised wording provided by Alberto Ganesh Babati after 5 positive votes on c++std-lib.
[ Adopted at 2010-11 Batavia ]
Proposed resolution:
explicit bitset(const char *str);template <class charT> explicit bitset( const charT *str, typename basic_string<charT>::size_type n = basic_string<charT>::npos, charT zero = charT('0'), charT one = charT('1'));
explicit bitset(const char *str);template <class charT> explicit bitset(const charT *str, typename basic_string<charT>::size_type n = basic_string<charT>::npos, charT zero = charT('0'), charT one = charT('1'));
Effects: Constructs an object of class
bitset<N> as if by
bitset(string(str)).
bitset( n == basic_string<charT>::npos ? basic_string<charT>(str) : basic_string<charT>(str, n), 0, n, zero, one)