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print(std::ostream)

Defined in header `<ostream>`
template< class... Args > void print( std::ostream& os, std::format_string<Args...> fmt, Args&&... args );		(since C++23)

Formats args according to the format string fmt, and inserts the result into os stream.

If the ordinary literal encoding is UTF-8, equivalent to:

std::vprint_unicode(os, fmt.get(), std::make_format_args(std::forward<Args>(args)...));

Otherwise, equivalent to:

std::vprint_nonunicode(os, fmt.get(), std::make_format_args(std::forward<Args>(args)...));

The behavior is undefined if std::formatter<Ti, char> does not meet the BasicFormatter requirements for any Ti in Args (as required by std::make_format_args).

Parameters

os - output stream to insert data into

fmt

an object that represents the format string. The format string consists of

ordinary characters (except { and }), which are copied unchanged to the output,
escape sequences {{ and }}, which are replaced with { and } respectively in the output, and
replacement fields.

Each replacement field has the following format:

`{` arg-id (optional) `}`	(1)
`{` arg-id (optional) `:` format-spec `}`	(2)

1) replacement field without a format specification 2) replacement field with a format specification

arg-id	-	specifies the index of the argument in `args` whose value is to be used for formatting; if it is omitted, the arguments are used in order. The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic indexing is an error.
format-spec	-	the format specification defined by the `std::formatter` specialization for the corresponding argument.

For basic types and standard string types, the format specification is interpreted as standard format specification.
For chrono types, the format specification is interpreted as chrono format specification.
For std::thread::id, the format specification is interpreted as thread id format specification.
For other formattable types, the format specification is determined by user-defined formatter specializations.

args... - arguments to be formatted

Return value

(none).

Exceptions

std::bad_alloc on allocation failure.
Propagate any exception thrown by any formatter, e.g. std::format_error, without regard to the value of os.exceptions() and without turning on ios_base::badbit in the error state of os.
May throw ios_base::failure caused by os.setstate(ios_base::badbit) which is called if an insertion into os fails.

Notes

Feature-test macro	Value	Std	Comment
`__cpp_lib_print`	202207L	(C++23)	Formatted output
`__cpp_lib_format`	202207L	(C++23)	Exposing `std::basic_format_string`

Example

A link to test: Compiler Explorer.

#include <array>
#include <cctype>
#include <format>
#include <ranges>
#include <numbers>
#include <iostream>
 
int main()
{
    std::array<char, 24> buf;
    std::format_to(buf.begin(), "{:.15f}", std::numbers::sqrt2);
 
    unsigned num{}, sum{};
 
    auto v = buf
           | std::views::filter(isdigit)
           | std::views::transform([](char x) { return x - '0'; })
           | std::views::take_while([&sum](char) { return sum < 42; })
           ;
 
    for (auto n : v) {
        sum += n;
        ++num;
    }
 
#ifdef __cpp_lib_print
    std::print(
        std::cout,
        "√2 = {}...\n"
        "The sum of its first {} digits is {}{}\n",
        std::numbers::sqrt2, num, sum, '.'
    );
#else
    std::cout <<
    std::format(
        "√2 = {}...\n"
        "The sum of its first {} digits is {}{}\n",
        std::numbers::sqrt2, num, sum, '.'
    );
#endif
}

Output:

√2 = 1.4142135623730951...
The sum of its first 13 digits is 42.