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noexcept issues inbasic_stringSection: 27.4.3[basic.string]Status:C++14Submitter: Howard HinnantOpened: 2011-05-29Last modified: 2016-11-12
Priority:Not Prioritized
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Discussion:
The following inconsistencies regardingnoexcept forbasic_string are noted.
noexcept:void swap(basic_string& str);
But the global swap is markednoexcept:
template<class charT, class traits, class Allocator>void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>& rhs)noexcept;But only in the definition, not in the synopsis.
All comparison operators are markednoexcept in their definitions, but not in the synopsis.The compare function that takes a pointer:int compare(const charT *s) const;
is not markednoexcept. But some of the comparison functions which are markednoexcept (only in their definition) are specified to call the throwing compare operator:
template<class charT, class traits, class Allocator>bool operator==(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;Returns:
lhs.compare(rhs) == 0.
All functions with a narrow contract should not be declared asnoexcept according tothe guidelines presented inn3279.Among these narrow contract functions are theswap functions (23.2.2[container.requirements.general] p. 8) and functions with non-NULLconst charT* parameters.
[2011-06-08 Daniel provides wording]
[Bloomington, 2011]
Move to Ready
Proposed resolution:
This wording is relative to the FDIS. Both move-assignment operator and the movingassignfunction are not touched by this issue, because they are handled separately by issue2063(i).
Modify the header<string> synopsis in 27.4[string.classes] as indicated (Rationale: Addingnoexcept to these specific overloads is in sync withapplying the same rule to specific overloads of the member functionsfind,compare, etc.This approach deviates from that taken inn3279,but seems more consistent given similar application for comparable member functions):
#include <initializer_list>namespace std { […] template<class charT, class traits, class Allocator> bool operator==(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept; […] template<class charT, class traits, class Allocator> bool operator!=(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept; […] template<class charT, class traits, class Allocator> bool operator<(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept; […] template<class charT, class traits, class Allocator> bool operator>(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept; […] template<class charT, class traits, class Allocator> bool operator<=(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept; […] template<class charT, class traits, class Allocator> bool operator>=(const basic_string<charT,traits,Allocator>& lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept; […]}Modify the class templatebasic_string synopsis in 27.4.3[basic.string] as indicated (Remark 1: Thenoexcept at the move-constructor is fine, because even for asmall-object optimization there is no problem here, becausebasic_string::value_typeis required to be a non-array POD as of 27.1[strings.general] p1, Remark 2: Thisproposal removes thenoexcept at single character overloads offind,rfind,etc. because they are defined in terms of potentially allocating functions. It seems likean additional issue to me to change the semantics in terms of non-allocating functions andaddingnoexcept instead):
namespace std { template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> > class basic_string { public: […]// [string.ops], string operations: […] size_type find (charT c, size_type pos = 0) constnoexcept; […] size_type rfind(charT c, size_type pos = npos) constnoexcept; […] size_type find_first_of(charT c, size_type pos = 0) constnoexcept; […] size_type find_last_of (charT c, size_type pos = npos) constnoexcept; […] size_type find_first_not_of(charT c, size_type pos = 0) constnoexcept; […] size_type find_last_not_of (charT c, size_type pos = npos) constnoexcept; […] };}Modify 27.4.3.8.2[string.find] before p5 and before p7 as indicated:
size_type find(const charT* s, size_type pos = 0) constnoexcept;[…]size_type find(charT c, size_type pos = 0) constnoexcept;-7-Returns:
find(basic_string<charT,traits,Allocator>(1,c), pos).
Modify [string.rfind] before p7 as indicated:
size_type rfind(charT c, size_type pos = npos) constnoexcept;-7-Returns:
rfind(basic_string<charT,traits,Allocator>(1,c),pos).
Modify [string.find.first.of] before p7 as indicated:
size_type find_first_of(charT c, size_type pos = 0) constnoexcept;-7-Returns:
find_first_of(basic_string<charT,traits,Allocator>(1,c), pos).
Modify [string.find.last.of] before p7 as indicated:
size_type find_last_of(charT c, size_type pos = npos) constnoexcept;-7-Returns:
find_last_of(basic_string<charT,traits,Allocator>(1,c),pos).
Modify [string.find.first.not.of] before p7 as indicated:
size_type find_first_not_of(charT c, size_type pos = 0) constnoexcept;-7-Returns:
find_first_not_of(basic_string(1, c), pos).
Modify [string.find.last.not.of] before p7 as indicated:
size_type find_last_not_of(charT c, size_type pos = npos) constnoexcept;-7-Returns:
find_last_not_of(basic_string(1, c), pos).
Modify [string.operator==] before p2+p3 as indicated:
template<class charT, class traits, class Allocator>bool operator==(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept;[…]template<class charT, class traits, class Allocator>bool operator==(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;
Modify [string.op!=] before p2+p3 as indicated:
template<class charT, class traits, class Allocator>bool operator!=(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept;[…]template<class charT, class traits, class Allocator>bool operator!=(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;
Modify [string.op<] before p2+p3 as indicated:
template<class charT, class traits, class Allocator>bool operator<(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept;[…]template<class charT, class traits, class Allocator>bool operator<(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;
Modify [string.op>] before p2+p3 as indicated:
template<class charT, class traits, class Allocator>bool operator>(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept;[…]template<class charT, class traits, class Allocator>bool operator>(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;
Modify [string.op<=] before p2+p3 as indicated:
template<class charT, class traits, class Allocator>bool operator<=(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept;[…]template<class charT, class traits, class Allocator>bool operator<=(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;
Modify [string.op>=] before p2+p3 as indicated:
template<class charT, class traits, class Allocator>bool operator>=(const charT* lhs, const basic_string<charT,traits,Allocator>& rhs)noexcept;[…]template<class charT, class traits, class Allocator>bool operator>=(const basic_string<charT,traits,Allocator>& lhs, const charT* rhs)noexcept;
Modify 27.4.4.3[string.special] as indicated (Remark: The change ofthe semantics guarantees as of 16.3.2.4[structure.specifications] p4 that the "Throws: Nothing" element of member swap is implied):
template<class charT, class traits, class Allocator> void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>& rhs)noexcept;-1- Effects:Equivalent to
lhs.swap(rhs);