print(std::ostream)

 

C++

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Named requirements

Feature test macros (C++20)

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Ranges library (C++20)

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Symbols index

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Input/output library

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Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

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basic_spanbuf (C++23)

strstreambuf (deprecated in C++98)

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ios_base

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basic_istream

basic_ostream

basic_iostream

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basic_ifstream

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basic_istringstream

basic_ostringstream

basic_stringstream

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basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

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basic_osyncstream (C++20)

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streamoff

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iostream_category (C++11)

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std::basic_ostream

Global objects
coutwcout	cerrwcerr	clogwclog
Member functions
basic_ostream::basic_ostream
basic_ostream::~basic_ostream
basic_ostream::operator= (C++11)
Formatted output
basic_ostream::operator<<
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basic_ostream::put
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basic_ostream::tellp
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Miscellaneous
basic_ostream::flush
basic_ostream::swap (C++11)
Member classes
basic_ostream::sentry
Non-member functions
operator<<(std::basic_ostream)
print(std::ostream) (C++23)
println(std::ostream) (C++23)
vprint_unicode(std::ostream) (C++23)
vprint_nonunicode(std::ostream) (C++23)

 

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

Run this code

#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.

See also

println(std::ostream) (C++23)	outputs formatted representation of the arguments with appended '\n' (function template)
print (C++23)	prints to stdout or a file stream using formatted representation of the arguments (function template)
format (C++20)	stores formatted representation of the arguments in a new string (function template)