9.8 KiB
[support.srcloc]
17 Language support library [support]
17.8 Source location [support.srcloc]
17.8.1 Header <source_location> synopsis [source.location.syn]
The header <source_location> defines the class source_location that provides a means to obtain source location information.
// all freestandingnamespace std {struct source_location;}
17.8.2 Class source_location [support.srcloc.class]
17.8.2.1 General [support.srcloc.class.general]
namespace std {struct source_location {// source location constructionstatic consteval source_location current() noexcept; constexpr source_location() noexcept; // source location field accessconstexpr uint_least32_t line() const noexcept; constexpr uint_least32_t column() const noexcept; constexpr const char* file_name() const noexcept; constexpr const char* function_name() const noexcept; private: uint_least32_t line_; // exposition only uint_least32_t column_; // exposition onlyconst char* file_name_; // exposition onlyconst char* function_name_; // exposition only};}
The type source_location meets theCpp17DefaultConstructible,Cpp17CopyConstructible,Cpp17CopyAssignable,Cpp17Swappable, andCpp17Destructible requirements ([utility.arg.requirements], [swappable.requirements]).
All of the following conditions are true:
is_nothrow_move_constructible_v<source_location>
is_nothrow_move_assignable_v<source_location>
is_nothrow_swappable_v<source_location>
[Note 1:
The intent of source_location is to have a small size and efficient copying.
It is unspecified whether the copy/move constructors and the copy/move assignment operators are trivial and/or constexpr.
â end note]
The data members file_name_ and function_name_ always each refer to an ntbs.
The copy/move constructors and the copy/move assignment operators ofsource_location meet the following postconditions: Given two objects lhs and rhs of type source_location, where lhs is a copy/move result of rhs, and where rhs_p is a value denoting the state of rhs before the corresponding copy/move operation, then each of the following conditions is true:
strcmp(lhs.file_name(), rhs_p.file_name()) == 0
strcmp(lhs.function_name(), rhs_p.function_name()) == 0
lhs.line() == rhs_p.line()
lhs.column() == rhs_p.column()
17.8.2.2 Creation [support.srcloc.cons]
static consteval source_location current() noexcept;
Returns:
-
When invoked by a function call whose postfix-expression is a (possibly parenthesized) id-expression naming current, returns a source_location with an implementation-defined value. The value should be affected by #line ([cpp.line]) in the same manner as for LINE and FILE. The values of the exposition-only data members of the returned source_location object are indicated in Table 43. Table 43 — Value of object returned by current [tab:support.srcloc.current]
| ð Element |
Value |
|---|---|
| ð line_ |
A presumed line number ([cpp.predefined]). Line numbers are presumed to be 1-indexed; however, an implementation is encouraged to use 0 when the line number is unknown. |
| ð column_ |
An implementation-defined value denoting some offset from the start of the line denoted by line_. Column numbers are presumed to be 1-indexed; however, an implementation is encouraged to use 0 when the column number is unknown. |
| ð file_name_ |
A presumed name of the current source file ([cpp.predefined]) as an ntbs. |
| ð function_name_ |
A name of the current function such as in func ([dcl.fct.def.general]) if any, an empty string otherwise. |
-
Otherwise, when invoked in some other way, returns a source_location whose data members are initialized with valid but unspecified values.
Remarks: Any call to current that appears as a default member initializer ([class.mem.general]), or as a subexpression thereof, should correspond to the location of the constructor definition or aggregate initialization that uses the default member initializer.
Any call to current that appears as a default argument ([dcl.fct.default]), or as a subexpression thereof, should correspond to the location of the invocation of the function that uses the default argument ([expr.call]).
[Example 1: struct s { source_location member = source_location::current(); int other_member; s(source_location loc = source_location::current()): member(loc) // values of member refer to the location of the calling function ([dcl.fct.default]){} s(int blather) : // values of member refer to this location other_member(blather){} s(double) // values of member refer to this location{}};void f(source_location a = source_location::current()) { source_location b = source_location::current(); // values in b refer to this line}void g() { f(); // f's first argument corresponds to this line of code source_location c = source_location::current(); f(c); // f's first argument gets the same values as c, above} â end example]
constexpr source_location() noexcept;
Effects: The data members are initialized with valid but unspecified values.
17.8.2.3 Observers [support.srcloc.obs]
constexpr uint_least32_t line() const noexcept;
Returns: line_.
constexpr uint_least32_t column() const noexcept;
Returns: column_.
constexpr const char* file_name() const noexcept;
Returns: file_name_.
constexpr const char* function_name() const noexcept;
Returns: function_name_.