std:: runtime_format
|
Defined in header
<format>
|
||
|
/*runtime-format-string*/
<
char
>
runtime_format
(
std::
string_view
fmt
)
noexcept
;
|
(1) | (since C++26) |
|
/*runtime-format-string*/
<
wchar_t
>
runtime_format
(
std::
wstring_view
fmt
)
noexcept
;
|
(2) | (since C++26) |
Returns an object that stores a runtime format string directly usable in user-oriented formatting functions and can be implicitly converted to
std::basic_format_string
.
Parameters
| fmt | - | a string view |
Return value
An object holding the runtime format string of the exposition-only type:
Class template
runtime-format-string
<CharT>
|
template
<
class
CharT
>
struct /*runtime-format-string*/ ; |
( exposition only* ) | |
Member objects
The returned object contains an exposition-only non-static data member
str
of type
std::basic_string_view<CharT>
.
Constructors and assignments
|
/*runtime-format-string*/
(
std::
basic_string_view
<
CharT
>
s
)
noexcept
;
|
(1) | |
|
/*runtime-format-string*/
(
const
/*runtime-format-string*/
&
)
=
delete
;
|
(2) | |
|
/*runtime-format-string*/
&
operator
=
(
const
/*runtime-format-string*/
&
)
=
delete
;
|
(3) | |
str
with
s
.
Notes
Since the return type of
runtime_format
is neither copyable nor movable, an attempt of passing
runtime_fmt
as glvalue inhibits the construction of
std::basic_format_string
which results in program ill-formed. To construct
std::basic_format_string
with
runtime_format
, the returned value of
runtime_format
is passed directly on
std::basic_format_string
as prvalue where copy elision is guaranteed.
auto runtime_fmt = std::runtime_format("{}"); auto s0 = std::format(runtime_fmt, 1); // error auto s1 = std::format(std::move(runtime_fmt), 1); // still error auto s2 = std::format(std::runtime_format("{}"), 1); // ok
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_format
|
202311L | (C++26) | Runtime format strings |
Example
#include <format> #include <print> #include <string> #include <string_view> int main() { std::print("Hello {}!\n", "world"); std::string fmt; for (int i{}; i != 3; ++i) { fmt += "{} "; // constructs the formatting string std::print("{} : ", fmt); std::println(std::runtime_format(fmt), "alpha", 'Z', 3.14, "unused"); } }
Output:
Hello world!
{} : alpha
{} {} : alpha Z
{} {} {} : alpha Z 3.14
See also
|
(C++20)
|
stores formatted representation of the arguments in a new string
(function template) |
|
(C++20)
|
non-template variant of
std::format
using type-erased argument representation
(function) |
|
(C++20)
(C++20)
(C++20)
|
class template that performs compile-time format string checks at construction time
(class template) |