std::runtime_format
From cppreference.com
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) | |
1) Initializes
str with s.2) Copy constructor is explicitly deleted. The type is neither copyable nor movable.
3) The assignment is explicitly deleted.
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
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
Run this code
#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 3.14See 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) |