19 Diagnostics library [diagnostics]

19.6 Stacktrace [stacktrace]

19.6.1 General [stacktrace.general]

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.

The invocation sequence of the current evaluation

x_{0}

in the current thread of execution is a sequence

(x_{0}, \dots, x_{n})

of evaluations such that, for i ≥ 0,

x_{i}

is within the function invocation

x_{i + 1}

([intro.execution]).

A stacktrace is an approximate representation of an invocation sequence and consists of stacktrace entries.

A stacktrace entry represents an evaluation in a stacktrace.

19.6.2 Header <stacktrace> synopsis [stacktrace.syn]

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#include <compare> // see [compare.syn] namespace std { // [stacktrace.entry], class stacktrace_entry class stacktrace_entry; // [stacktrace.basic], class template basic_stacktrace template<class Allocator> class basic_stacktrace; // basic_stacktrace typedef-names using stacktrace = basic_stacktrace<allocator<stacktrace_entry>>; // [stacktrace.basic.nonmem], non-member functions template<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], formatting support template<> 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], hash support template<class T> struct hash; template<> struct hash<stacktrace_entry>; template<class Allocator> struct hash<basic_stacktrace<Allocator>>; }

19.6.3 Class stacktrace_entry [stacktrace.entry]

19.6.3.1 Overview [stacktrace.entry.overview]

namespace std { class stacktrace_entry { public: using native_handle_type = implementation-defined; // [stacktrace.entry.cons], constructors constexpr 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], observers constexpr native_handle_type native_handle() const noexcept; constexpr explicit operator bool() const noexcept; // [stacktrace.entry.query], query string description() const; string source_file() const; uint_least32_t source_line() const; // [stacktrace.entry.cmp], comparison friend 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; }; }

An object of type stacktrace_entry is either empty, or represents a stacktrace entry and provides operations for querying information about it.

The class stacktrace_entry models regular ([concepts.object]) and three_way_comparable<strong_ordering> ([cmp.concept]).

19.6.3.2 Constructors [stacktrace.entry.cons]

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constexpr stacktrace_entry() noexcept;

Postconditions: *this is empty.

19.6.3.3 Observers [stacktrace.entry.obs]

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constexpr native_handle_type native_handle() const noexcept;

The semantics of this function are implementation-defined.

Remarks: Successive invocations of the native_handle function for an unchanged stacktrace_entry object return identical values.

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constexpr explicit operator bool() const noexcept;

Returns: false if and only if *this is empty.

19.6.3.4 Query [stacktrace.entry.query]

[Note 1:

All the stacktrace_entry query functions treat errors other than memory allocation errors as “no information available” and do not throw in that case.

— end note]

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string description() const;

Returns: A description of the evaluation represented by *this, or an empty string.

Throws: bad_alloc if memory for the internal data structures or the resulting string cannot be allocated.

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string source_file() const;

Returns: The presumed or actual name of the source file ([cpp.predefined]) that lexically contains the expression or statement whose evaluation is represented by *this, or an empty string.

Throws: bad_alloc if memory for the internal data structures or the resulting string cannot be allocated.

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uint_least32_t source_line() const;

Returns: 0, or a 1-based line number that lexically relates to the evaluation represented by *this.

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.

Throws: bad_alloc if memory for the internal data structures cannot be allocated.

19.6.3.5 Comparison [stacktrace.entry.cmp]

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

Returns: true if and only if x and y represent the same stacktrace entry or both x and y are empty.

19.6.4 Class template basic_stacktrace [stacktrace.basic]

19.6.4.1 Overview [stacktrace.basic.overview]

namespace std { template<class Allocator> class basic_stacktrace { 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] 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], creation and assignment static 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], 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; [[nodiscard]] 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], comparisons template<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], modifiers void 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 }; }

The class template basic_stacktrace satisfies the requirements of a reversible container ([container.rev.reqmts]), of an allocator-aware container ([container.alloc.reqmts]), and of a sequence container ([sequence.reqmts]), except that

(1.1)
only move, assignment, swap, and operations defined for const-qualified sequence containers are supported and,
(1.2)
the semantics of comparison functions are different from those required for a container.

19.6.4.2 Creation and assignment [stacktrace.basic.cons]

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

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.

alloc is passed to the constructor of the frames_ object.

[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.

— end note]

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

Let t be a stacktrace as-if obtained via basic_stacktrace::current(alloc).

Let n be t.size().

Returns: A basic_stacktrace object where frames_ is direct-non-list-initialized from arguments t.begin() + min(n, skip), t.end(), and alloc, or an empty basic_stacktrace object if the initialization of frames_ failed.

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

Let t be a stacktrace as-if obtained via basic_stacktrace::current(alloc).

Let n be t.size().

Preconditions: skip <= skip + max_depth is true.

Returns: A basic_stacktrace object where frames_ is direct-non-list-initialized from arguments t.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.

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basic_stacktrace() noexcept(is_nothrow_default_constructible_v<allocator_type>);

Postconditions: empty() is true.

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explicit basic_stacktrace(const allocator_type& alloc) noexcept;

Effects: alloc is passed to the frames_ constructor.

Postconditions: empty() is true.

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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);

Remarks: Implementations may strengthen the exception specification for these functions ([res.on.exception.handling]) by ensuring that empty() is true on failed allocation.

19.6.4.3 Observers [stacktrace.basic.obs]

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using const_iterator = implementation-defined;

The type models random_access_iterator ([iterator.concept.random.access]) and meets the Cpp17RandomAccessIterator requirements ([random.access.iterators]).

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allocator_type get_allocator() const noexcept;

Returns: frames_.get_allocator().

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

Returns: An iterator referring to the first element in frames_.

If empty() is true, then it returns the same value as end().

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

Returns: The end iterator.

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

Returns: reverse_iterator(cend()).

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

Returns: reverse_iterator(cbegin()).

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[[nodiscard]] bool empty() const noexcept;

Returns: frames_.empty().

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size_type size() const noexcept;

Returns: frames_.size().

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size_type max_size() const noexcept;

Returns: frames_.max_size().

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const_reference operator[](size_type frame_no) const;

Preconditions: frame_no < size() is true.

Returns: frames_[frame_no].

Throws: Nothing.

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const_reference at(size_type frame_no) const;

Returns: frames_[frame_no].

Throws: out_of_range if frame_no >= size().

19.6.4.4 Comparisons [stacktrace.basic.cmp]

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

Returns: equal(x.begin(), x.end(), y.begin(), y.end()).

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

Returns: x.size() <=> y.size() if x.size() != y.size(); lexicographical_compare_three_way(x.begin(), x.end(), y.begin(), y.end()) otherwise.

19.6.4.5 Modifiers [stacktrace.basic.mod]

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

Effects: Exchanges the contents of *this and other.

19.6.4.6 Non-member functions [stacktrace.basic.nonmem]

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

Effects: Equivalent to a.swap(b).

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string to_string(const stacktrace_entry& f);

Returns: A string with a description of f.

Recommended practice: The description should provide information about the contained evaluation, including information from f.source_file() and f.source_line().

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

Returns: A string with a description of st.

[Note 1:

The number of lines is not guaranteed to be equal to st.size().

— end note]

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

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

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

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

19.6.5 Formatting support [stacktrace.format]

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template<> struct formatter<stacktrace_entry>;

formatter<stacktrace_entry> interprets format-spec as a stacktrace-entry-format-spec.

The syntax of format specifications is as follows:

stacktrace-entry-format-spec:
fill-and-align

_{o p t}

width

_{o p t}

[Note 1:

The productions fill-and-align and width are described in [format.string.std].

— end note]

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.

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

For formatter<basic_stacktrace<Allocator>>, format-spec is empty.

A basic_stacktrace<Allocator> object s is formatted as if by copying to_string(s) through the output iterator of the context.

19.6.6 Hash support [stacktrace.basic.hash]

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

The specializations are enabled ([unord.hash]).