[stacktrace]

# 19 Diagnostics library [[diagnostics]](./#diagnostics)

## 19.6 Stacktrace [stacktrace]

### [19.6.1](#general) General [[stacktrace.general]](stacktrace.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1651)

Subclause [stacktrace] describes components
that C++ programs may use to store
the stacktrace of the current thread of execution and
query information about the stored stacktrace at runtime[.](#general-1.sentence-1)

[2](#general-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1657)

The [*invocation sequence*](#def:invocation_sequence "19.6.1 General [stacktrace.general]") of the current evaluation x0 in the current thread of execution
is a sequence (x0,â¦,xn) of evaluations such that, for i â¥ 0,xi is within the function invocation xi+1 ([[intro.execution]](intro.execution "6.10.1 Sequential execution"))[.](#general-2.sentence-1)

[3](#general-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1663)

A [*stacktrace*](#def:stacktrace "19.6.1 General [stacktrace.general]") is an approximate representation of
an invocation sequence and consists of stacktrace entries[.](#general-3.sentence-1)

A [*stacktrace entry*](#def:stacktrace_entry "19.6.1 General [stacktrace.general]") represents an evaluation in a stacktrace[.](#general-3.sentence-2)

### [19.6.2](#syn) Header <stacktrace> synopsis [[stacktrace.syn]](stacktrace.syn)

[ð](#header:%3cstacktrace%3e)

#include <compare> // see [[compare.syn]](compare.syn "17.12.1 Header <compare> synopsis")namespace std {// [[stacktrace.entry]](#entry "19.6.3 Class stacktrace_­entry"), class stacktrace_entryclass stacktrace_entry; // [[stacktrace.basic]](#basic "19.6.4 Class template basic_­stacktrace"), class template basic_stacktracetemplate<class Allocator>class basic_stacktrace; // basic_stacktrace [*typedef-name*](dcl.typedef#nt:typedef-name "9.2.4 The typedef specifier [dcl.typedef]")*s*using stacktrace = basic_stacktrace<allocator<stacktrace_entry>>; // [[stacktrace.basic.nonmem]](#basic.nonmem "19.6.4.6 Non-member functions"), non-member functionstemplate<class Allocator>void swap(basic_stacktrace<Allocator>& a, basic_stacktrace<Allocator>& b)noexcept(noexcept(a.swap(b)));

 string to_string(const stacktrace_entry& f); template<class Allocator> string to_string(const basic_stacktrace<Allocator>& st);

 ostream& operator<<(ostream& os, const stacktrace_entry& f); template<class Allocator> ostream& operator<<(ostream& os, const basic_stacktrace<Allocator>& st); // [[stacktrace.format]](#format "19.6.5 Formatting support"), formatting supporttemplate<> struct formatter<stacktrace_entry>; template<class Allocator> struct formatter<basic_stacktrace<Allocator>>; namespace pmr {using stacktrace = basic_stacktrace<polymorphic_allocator<stacktrace_entry>>; }// [[stacktrace.basic.hash]](#basic.hash "19.6.6 Hash support"), hash supporttemplate<class T> struct hash; template<> struct hash<stacktrace_entry>; template<class Allocator> struct hash<basic_stacktrace<Allocator>>;}

### [19.6.3](#entry) Class stacktrace_entry [[stacktrace.entry]](stacktrace.entry)

#### [19.6.3.1](#entry.overview) Overview [[stacktrace.entry.overview]](stacktrace.entry.overview)

namespace std {class [stacktrace_entry](#lib:stacktrace_entry "19.6.3.1 Overview [stacktrace.entry.overview]") {public:using native_handle_type = *implementation-defined*; // [[stacktrace.entry.cons]](#entry.cons "19.6.3.2 Constructors"), constructorsconstexpr stacktrace_entry() noexcept; constexpr stacktrace_entry(const stacktrace_entry& other) noexcept; constexpr stacktrace_entry& operator=(const stacktrace_entry& other) noexcept; ~stacktrace_entry(); // [[stacktrace.entry.obs]](#entry.obs "19.6.3.3 Observers"), observersconstexpr native_handle_type native_handle() const noexcept; constexpr explicit operator bool() const noexcept; // [[stacktrace.entry.query]](#entry.query "19.6.3.4 Query"), query string description() const;
 string source_file() const;
 uint_least32_t source_line() const; // [[stacktrace.entry.cmp]](#entry.cmp "19.6.3.5 Comparison"), comparisonfriend constexpr bool operator==(const stacktrace_entry& x, const stacktrace_entry& y) noexcept; friend constexpr strong_ordering operator<=>(const stacktrace_entry& x, const stacktrace_entry& y) noexcept; };}

[1](#entry.overview-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1749)

An object of type stacktrace_entry is either empty,
or represents a stacktrace entry and
provides operations for querying information about it[.](#entry.overview-1.sentence-1)

The class stacktrace_entry models[regular](concepts.object#concept:regular "18.6 Object concepts [concepts.object]") ([[concepts.object]](concepts.object "18.6 Object concepts")) and[three_way_comparable](cmp.concept#concept:three_way_comparable "17.12.4 Concept three_­way_­comparable [cmp.concept]")<strong_ordering> ([[cmp.concept]](cmp.concept "17.12.4 Concept three_­way_­comparable"))[.](#entry.overview-1.sentence-2)

#### [19.6.3.2](#entry.cons) Constructors [[stacktrace.entry.cons]](stacktrace.entry.cons)

[ð](#lib:stacktrace_entry,constructor)

`constexpr stacktrace_entry() noexcept;
`

[1](#entry.cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1765)

*Postconditions*: *this is empty[.](#entry.cons-1.sentence-1)

#### [19.6.3.3](#entry.obs) Observers [[stacktrace.entry.obs]](stacktrace.entry.obs)

[ð](#lib:native_handle,stacktrace_entry)

`constexpr native_handle_type native_handle() const noexcept;
`

[1](#entry.obs-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1778)

The semantics of this function areimplementation-defined[.](#entry.obs-1.sentence-1)

[2](#entry.obs-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1782)

*Remarks*: Successive invocations of the native_handle function
for an unchanged stacktrace_entry object return identical values[.](#entry.obs-2.sentence-1)

[ð](#lib:operator_bool,stacktrace_entry)

`constexpr explicit operator bool() const noexcept;
`

[3](#entry.obs-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1794)

*Returns*: false if and only if *this is empty[.](#entry.obs-3.sentence-1)

#### [19.6.3.4](#entry.query) Query [[stacktrace.entry.query]](stacktrace.entry.query)

[1](#entry.query-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1801)

[*Note [1](#entry.query-note-1)*:

All the stacktrace_entry query functions treat
errors other than memory allocation errors
as âno information availableâ and do not throw in that case[.](#entry.query-1.sentence-1)

â *end note*]

[ð](#lib:description,stacktrace_entry)

`string description() const;
`

[2](#entry.query-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1814)

*Returns*: A description of the evaluation represented by *this,
or an empty string[.](#entry.query-2.sentence-1)

[3](#entry.query-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1819)

*Throws*: bad_alloc if memory for
the internal data structures or the resulting string cannot be allocated[.](#entry.query-3.sentence-1)

[ð](#lib:source_file,stacktrace_entry)

`string source_file() const;
`

[4](#entry.query-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1831)

*Returns*: The presumed or actual name of the source file ([[cpp.predefined]](cpp.predefined "15.12 Predefined macro names"))
that lexically contains the expression or statement
whose evaluation is represented by *this, or an empty string[.](#entry.query-4.sentence-1)

[5](#entry.query-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1837)

*Throws*: bad_alloc if memory for
the internal data structures or the resulting string cannot be allocated[.](#entry.query-5.sentence-1)

[ð](#lib:source_line,stacktrace_entry)

`uint_least32_t source_line() const;
`

[6](#entry.query-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1849)

*Returns*: 0, or a 1-based line number that lexically relates to the evaluation
represented by *this[.](#entry.query-6.sentence-1)

If source_file returns the presumed name of the source file,
returns the presumed line number;
if source_file returns the actual name of the source file,
returns the actual line number[.](#entry.query-6.sentence-2)

[7](#entry.query-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1858)

*Throws*: bad_alloc if memory for
the internal data structures cannot be allocated[.](#entry.query-7.sentence-1)

#### [19.6.3.5](#entry.cmp) Comparison [[stacktrace.entry.cmp]](stacktrace.entry.cmp)

[ð](#lib:operator==,stacktrace_entry)

`friend constexpr bool operator==(const stacktrace_entry& x, const stacktrace_entry& y) noexcept;
`

[1](#entry.cmp-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1872)

*Returns*: true if and only if x and y represent
the same stacktrace entry or both x and y are empty[.](#entry.cmp-1.sentence-1)

### [19.6.4](#basic) Class template basic_stacktrace [[stacktrace.basic]](stacktrace.basic)

#### [19.6.4.1](#basic.overview) Overview [[stacktrace.basic.overview]](stacktrace.basic.overview)

namespace std {template<class Allocator>class [basic_stacktrace](#lib:basic_stacktrace "19.6.4.1 Overview [stacktrace.basic.overview]") {public:using value_type = stacktrace_entry; using const_reference = const value_type&; using reference = value_type&; using const_iterator = *implementation-defined*; // see [[stacktrace.basic.obs]](#basic.obs "19.6.4.3 Observers")using iterator = const_iterator; using reverse_iterator = std::reverse_iterator<iterator>; using const_reverse_iterator = std::reverse_iterator<const_iterator>; using difference_type = *implementation-defined*; using size_type = *implementation-defined*; using allocator_type = Allocator; // [[stacktrace.basic.cons]](#basic.cons "19.6.4.2 Creation and assignment"), creation and assignmentstatic basic_stacktrace current(const allocator_type& alloc = allocator_type()) noexcept; static basic_stacktrace current(size_type skip, const allocator_type& alloc = allocator_type()) noexcept; static basic_stacktrace current(size_type skip, size_type max_depth, const allocator_type& alloc = allocator_type()) noexcept;

 basic_stacktrace() noexcept(is_nothrow_default_constructible_v<allocator_type>); explicit basic_stacktrace(const allocator_type& alloc) noexcept;

 basic_stacktrace(const basic_stacktrace& other);
 basic_stacktrace(basic_stacktrace&& other) noexcept;
 basic_stacktrace(const basic_stacktrace& other, const allocator_type& alloc);
 basic_stacktrace(basic_stacktrace&& other, const allocator_type& alloc);
 basic_stacktrace& operator=(const basic_stacktrace& other);
 basic_stacktrace& operator=(basic_stacktrace&& other)noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value || allocator_traits<Allocator>::is_always_equal::value); ~basic_stacktrace(); // [[stacktrace.basic.obs]](#basic.obs "19.6.4.3 Observers"), observers allocator_type get_allocator() const noexcept;

 const_iterator begin() const noexcept;
 const_iterator end() const noexcept;
 const_reverse_iterator rbegin() const noexcept;
 const_reverse_iterator rend() const noexcept;

 const_iterator cbegin() const noexcept;
 const_iterator cend() const noexcept;
 const_reverse_iterator crbegin() const noexcept;
 const_reverse_iterator crend() const noexcept; bool empty() const noexcept;
 size_type size() const noexcept;
 size_type max_size() const noexcept;

 const_reference operator[](size_type) const;
 const_reference at(size_type) const; // [[stacktrace.basic.cmp]](#basic.cmp "19.6.4.4 Comparisons"), comparisonstemplate<class Allocator2>friend bool operator==(const basic_stacktrace& x, const basic_stacktrace<Allocator2>& y) noexcept; template<class Allocator2>friend strong_ordering operator<=>(const basic_stacktrace& x, const basic_stacktrace<Allocator2>& y) noexcept; // [[stacktrace.basic.mod]](#basic.mod "19.6.4.5 Modifiers"), modifiersvoid swap(basic_stacktrace& other)noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value || allocator_traits<Allocator>::is_always_equal::value); private: vector<value_type, allocator_type> *frames_*; // *exposition only*};}

[1](#basic.overview-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1958)

The class template basic_stacktrace satisfies
the requirements
of a reversible container ([[container.rev.reqmts]](container.rev.reqmts "23.2.2.3 Reversible container requirements")),
of an allocator-aware container ([[container.alloc.reqmts]](container.alloc.reqmts "23.2.2.5 Allocator-aware containers")), and
of a sequence container ([[sequence.reqmts]](sequence.reqmts "23.2.4 Sequence containers")),
except that

- [(1.1)](#basic.overview-1.1)

only move, assignment, swap, and
operations defined for const-qualified sequence containers are supported and,

- [(1.2)](#basic.overview-1.2)

the semantics of comparison functions
are different from those required for a container[.](#basic.overview-1.sentence-1)

#### [19.6.4.2](#basic.cons) Creation and assignment [[stacktrace.basic.cons]](stacktrace.basic.cons)

[ð](#lib:current,basic_stacktrace)

`static basic_stacktrace current(const allocator_type& alloc = allocator_type()) noexcept;
`

[1](#basic.cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1982)

*Returns*: A basic_stacktrace object
with *frames_* storing
the stacktrace of the current evaluation in the current thread of execution, or
an empty basic_stacktrace object
if the initialization of *frames_* failed[.](#basic.cons-1.sentence-1)

alloc is passed to the constructor of the *frames_* object[.](#basic.cons-1.sentence-2)

[*Note [1](#basic.cons-note-1)*:

If the stacktrace was successfully obtained,
then *frames_*.front() is the stacktrace_entry representing approximately the current evaluation, and*frames_*.back() is the stacktrace_entry representing approximately the initial function of
the current thread of execution[.](#basic.cons-1.sentence-3)

â *end note*]

[ð](#lib:current,basic_stacktrace_)

`static basic_stacktrace current(size_type skip,
                                const allocator_type& alloc = allocator_type()) noexcept;
`

[2](#basic.cons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2008)

Let t be a stacktrace
as-if obtained via basic_stacktrace​::​current(alloc)[.](#basic.cons-2.sentence-1)

Let n be t.size()[.](#basic.cons-2.sentence-2)

[3](#basic.cons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2013)

*Returns*: A basic_stacktrace object
where *frames_* is direct-non-list-initialized from argumentst.begin() + min(n, skip), t.end(), and alloc,
or an empty basic_stacktrace object
if the initialization of *frames_* failed[.](#basic.cons-3.sentence-1)

[ð](#lib:current,basic_stacktrace__)

`static basic_stacktrace current(size_type skip, size_type max_depth,
                                const allocator_type& alloc = allocator_type()) noexcept;
`

[4](#basic.cons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2029)

Let t be a stacktrace
as-if obtained via basic_stacktrace​::​current(alloc)[.](#basic.cons-4.sentence-1)

Let n be t.size()[.](#basic.cons-4.sentence-2)

[5](#basic.cons-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2034)

*Hardened preconditions*: skip <= skip + max_depth is true[.](#basic.cons-5.sentence-1)

[6](#basic.cons-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2038)

*Returns*: A basic_stacktrace object
where *frames_* is direct-non-list-initialized from argumentst.begin() + min(n, skip), t.begin() + min(n, skip + max_depth),
and alloc,
or an empty basic_stacktrace object
if the initialization of *frames_* failed[.](#basic.cons-6.sentence-1)

[ð](#lib:basic_stacktrace,constructor)

`basic_stacktrace() noexcept(is_nothrow_default_constructible_v<allocator_type>);
`

[7](#basic.cons-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2054)

*Postconditions*: empty() is true[.](#basic.cons-7.sentence-1)

[ð](#lib:basic_stacktrace,constructor_)

`explicit basic_stacktrace(const allocator_type& alloc) noexcept;
`

[8](#basic.cons-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2065)

*Effects*: alloc is passed to the *frames_* constructor[.](#basic.cons-8.sentence-1)

[9](#basic.cons-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2069)

*Postconditions*: empty() is true[.](#basic.cons-9.sentence-1)

[ð](#lib:basic_stacktrace,constructor__)

`basic_stacktrace(const basic_stacktrace& other);
basic_stacktrace(const basic_stacktrace& other, const allocator_type& alloc);
basic_stacktrace(basic_stacktrace&& other, const allocator_type& alloc);
basic_stacktrace& operator=(const basic_stacktrace& other);
basic_stacktrace& operator=(basic_stacktrace&& other)
  noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
    allocator_traits<Allocator>::is_always_equal::value);
`

[10](#basic.cons-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2087)

*Remarks*: Implementations may strengthen the exception specification
for these functions ([[res.on.exception.handling]](res.on.exception.handling "16.4.6.14 Restrictions on exception handling"))
by ensuring that empty() is true on failed allocation[.](#basic.cons-10.sentence-1)

#### [19.6.4.3](#basic.obs) Observers [[stacktrace.basic.obs]](stacktrace.basic.obs)

[ð](#lib:const_iterator,basic_stacktrace)

`using const_iterator = implementation-defined;
`

[1](#basic.obs-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2102)

The type models[random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") ([[iterator.concept.random.access]](iterator.concept.random.access "24.3.4.13 Concept random_­access_­iterator")) and
meets the*Cpp17RandomAccessIterator* requirements ([[random.access.iterators]](random.access.iterators "24.3.5.7 Random access iterators"))[.](#basic.obs-1.sentence-1)

[ð](#lib:get_allocator,basic_stacktrace)

`allocator_type get_allocator() const noexcept;
`

[2](#basic.obs-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2115)

*Returns*: *frames_*.get_allocator()[.](#basic.obs-2.sentence-1)

[ð](#lib:begin,basic_stacktrace)

`const_iterator begin() const noexcept;
const_iterator cbegin() const noexcept;
`

[3](#basic.obs-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2128)

*Returns*: An iterator referring to the first element in *frames_*[.](#basic.obs-3.sentence-1)

If empty() is true,
then it returns the same value as end()[.](#basic.obs-3.sentence-2)

[ð](#lib:end,basic_stacktrace)

`const_iterator end() const noexcept;
const_iterator cend() const noexcept;
`

[4](#basic.obs-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2143)

*Returns*: The end iterator[.](#basic.obs-4.sentence-1)

[ð](#lib:rbegin,basic_stacktrace)

`const_reverse_iterator rbegin() const noexcept;
const_reverse_iterator crbegin() const noexcept;
`

[5](#basic.obs-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2156)

*Returns*: reverse_iterator(cend())[.](#basic.obs-5.sentence-1)

[ð](#lib:rend,basic_stacktrace)

`const_reverse_iterator rend() const noexcept;
const_reverse_iterator crend() const noexcept;
`

[6](#basic.obs-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2169)

*Returns*: reverse_iterator(cbegin())[.](#basic.obs-6.sentence-1)

[ð](#lib:empty,basic_stacktrace)

`bool empty() const noexcept;
`

[7](#basic.obs-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2180)

*Returns*: *frames_*.empty()[.](#basic.obs-7.sentence-1)

[ð](#lib:size,basic_stacktrace)

`size_type size() const noexcept;
`

[8](#basic.obs-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2191)

*Returns*: *frames_*.size()[.](#basic.obs-8.sentence-1)

[ð](#lib:max_size,basic_stacktrace)

`size_type max_size() const noexcept;
`

[9](#basic.obs-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2202)

*Returns*: *frames_*.max_size()[.](#basic.obs-9.sentence-1)

[ð](#lib:operator%5b%5d,basic_stacktrace)

`const_reference operator[](size_type frame_no) const;
`

[10](#basic.obs-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2213)

*Hardened preconditions*: frame_no < size() is true[.](#basic.obs-10.sentence-1)

[11](#basic.obs-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2217)

*Returns*: *frames_*[frame_no][.](#basic.obs-11.sentence-1)

[12](#basic.obs-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2221)

*Throws*: Nothing[.](#basic.obs-12.sentence-1)

[ð](#lib:at,basic_stacktrace)

`const_reference at(size_type frame_no) const;
`

[13](#basic.obs-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2232)

*Returns*: *frames_*[frame_no][.](#basic.obs-13.sentence-1)

[14](#basic.obs-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2236)

*Throws*: out_of_range if frame_no >= size()[.](#basic.obs-14.sentence-1)

#### [19.6.4.4](#basic.cmp) Comparisons [[stacktrace.basic.cmp]](stacktrace.basic.cmp)

[ð](#lib:operator==,basic_stacktrace)

`template<class Allocator2>
friend bool operator==(const basic_stacktrace& x, const basic_stacktrace<Allocator2>& y) noexcept;
`

[1](#basic.cmp-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2250)

*Returns*: equal(x.begin(), x.end(), y.begin(), y.end())[.](#basic.cmp-1.sentence-1)

[ð](#lib:operator%3c=%3e,basic_stacktrace)

`template<class Allocator2>
friend strong_ordering
  operator<=>(const basic_stacktrace& x, const basic_stacktrace<Allocator2>& y) noexcept;
`

[2](#basic.cmp-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2263)

*Returns*: x.size() <=> y.size() if x.size() != y.size();lexicographical_compare_three_way(x.begin(), x.end(), y.begin(), y.end()) otherwise[.](#basic.cmp-2.sentence-1)

#### [19.6.4.5](#basic.mod) Modifiers [[stacktrace.basic.mod]](stacktrace.basic.mod)

[ð](#lib:swap,basic_stacktrace)

`void swap(basic_stacktrace& other)
  noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
    allocator_traits<Allocator>::is_always_equal::value);
`

[1](#basic.mod-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2280)

*Effects*: Exchanges the contents of *this and other[.](#basic.mod-1.sentence-1)

#### [19.6.4.6](#basic.nonmem) Non-member functions [[stacktrace.basic.nonmem]](stacktrace.basic.nonmem)

[ð](#lib:swap,basic_stacktrace_)

`template<class Allocator>
void swap(basic_stacktrace<Allocator>& a, basic_stacktrace<Allocator>& b)
  noexcept(noexcept(a.swap(b)));
`

[1](#basic.nonmem-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2295)

*Effects*: Equivalent to a.swap(b)[.](#basic.nonmem-1.sentence-1)

[ð](#lib:to_string,basic_stacktrace)

`string to_string(const stacktrace_entry& f);
`

[2](#basic.nonmem-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2306)

*Returns*: A string with a description of f[.](#basic.nonmem-2.sentence-1)

[3](#basic.nonmem-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2310)

*Recommended practice*: The description should provide information about the contained evaluation,
including information fromf.source_file() and f.source_line()[.](#basic.nonmem-3.sentence-1)

[ð](#lib:to_string,basic_stacktrace_)

`template<class Allocator>
string to_string(const basic_stacktrace<Allocator>& st);
`

[4](#basic.nonmem-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2324)

*Returns*: A string with a description of st[.](#basic.nonmem-4.sentence-1)

[*Note [1](#basic.nonmem-note-1)*:

The number of lines is not guaranteed to be equal to st.size()[.](#basic.nonmem-4.sentence-2)

â *end note*]

[ð](#lib:operator%3c%3c,stacktrace_entry)

`ostream& operator<<(ostream& os, const stacktrace_entry& f);
`

[5](#basic.nonmem-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2338)

*Effects*: Equivalent to: return os << to_string(f);

[ð](#lib:operator%3c%3c,basic_stacktrace)

`template<class Allocator>
  ostream& operator<<(ostream& os, const basic_stacktrace<Allocator>& st);
`

[6](#basic.nonmem-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2350)

*Effects*: Equivalent to: return os << to_string(st);

### [19.6.5](#format) Formatting support [[stacktrace.format]](stacktrace.format)

[ð](#format-itemdecl:1)

`template<> struct formatter<stacktrace_entry>;
`

[1](#format-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2362)

formatter<stacktrace_entry> interprets *format-spec* as a *stacktrace-entry-format-spec*[.](#format-1.sentence-1)

The syntax of format specifications is as follows:

stacktrace-entry-format-spec :  
fill-and-alignopt widthopt

[*Note [1](#format-note-1)*:

The productions *fill-and-align* and *width* are described in [[format.string.std]](format.string.std "28.5.2.2 Standard format specifiers")[.](#format-1.sentence-3)

â *end note*]

[2](#format-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2377)

A stacktrace_entry object se is formatted as if by
copying to_string(se) through the output iterator of the context
with additional padding and adjustments as specified by the format specifiers[.](#format-2.sentence-1)

[ð](#format-itemdecl:2)

`template<class Allocator> struct formatter<basic_stacktrace<Allocator>>;
`

[3](#format-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2388)

For formatter<basic_stacktrace<Allocator>>,*format-spec* is empty[.](#format-3.sentence-1)

[4](#format-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2392)

A basic_stacktrace<Allocator> object s is formatted as if by
copying to_string(s) through the output iterator of the context[.](#format-4.sentence-1)

### [19.6.6](#basic.hash) Hash support [[stacktrace.basic.hash]](stacktrace.basic.hash)

[ð](#basic.hash-itemdecl:1)

`template<> struct hash<stacktrace_entry>;
template<class Allocator> struct hash<basic_stacktrace<Allocator>>;
`

[1](#basic.hash-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L2405)

The specializations are enabled ([[unord.hash]](unord.hash "22.10.19 Class template hash"))[.](#basic.hash-1.sentence-1)
