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 in the current thread of execution is a sequence of evaluations such that, for i  β‰₯ 0, is within the function invocation ([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]

#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]

constexpr stacktrace_entry() noexcept;
Postconditions: *this is empty.

19.6.3.3 Observers [stacktrace.entry.obs]

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.
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 β€œno information available” and do not throw in that case.
β€” end note]
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.
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.
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]

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

19.6.4.2 Creation and assignment [stacktrace.basic.cons]

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.
β€” end note]
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.
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.
basic_stacktrace() noexcept(is_nothrow_default_constructible_v<allocator_type>);
Postconditions: empty() is true.
explicit basic_stacktrace(const allocator_type& alloc) noexcept;
Effects: alloc is passed to the frames_ constructor.
Postconditions: empty() is true.
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]

using const_iterator = implementation-defined;
The type models random_access_iterator ([iterator.concept.random.access]) and meets the Cpp17RandomAccessIterator requirements ([random.access.iterators]).
allocator_type get_allocator() const noexcept;
Returns: frames_.get_allocator().
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().
const_iterator end() const noexcept; const_iterator cend() const noexcept;
Returns: The end iterator.
const_reverse_iterator rbegin() const noexcept; const_reverse_iterator crbegin() const noexcept;
Returns: reverse_iterator(cend()).
const_reverse_iterator rend() const noexcept; const_reverse_iterator crend() const noexcept;
Returns: reverse_iterator(cbegin()).
[[nodiscard]] bool empty() const noexcept;
Returns: frames_.empty().
size_type size() const noexcept;
Returns: frames_.size().
size_type max_size() const noexcept;
Returns: frames_.max_size().
const_reference operator[](size_type frame_no) const;
Preconditions: frame_no < size() is true.
Returns: frames_[frame_no].
Throws: Nothing.
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]

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()).
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]

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]

template<class Allocator> void swap(basic_stacktrace<Allocator>& a, basic_stacktrace<Allocator>& b) noexcept(noexcept(a.swap(b)));
Effects: Equivalent to a.swap(b).
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().
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().
β€” end note]
ostream& operator<<(ostream& os, const stacktrace_entry& f);
Effects: Equivalent to: return os << to_string(f);
template<class Allocator> ostream& operator<<(ostream& os, const basic_stacktrace<Allocator>& st);
Effects: Equivalent to: return os << to_string(st);

19.6.4.7 Formatting support [stacktrace.format]

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 width
[Note 1: 
The productions fill-and-align and width are described in [format.string.std].
β€” 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.
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.

19.6.4.8 Hash support [stacktrace.basic.hash]

template<> struct hash<stacktrace_entry>; template<class Allocator> struct hash<basic_stacktrace<Allocator>>;
The specializations are enabled ([unord.hash]).