std::basic_ispanstream<CharT,Traits>::span

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

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Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

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basic_ifstream

basic_ofstream

basic_fstream

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basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::basic_ispanstream

Member functions

basic_ispanstream::basic_ispanstream (C++23)

basic_ispanstream::operator= (C++23)

basic_ispanstream::swap (C++23)

basic_ispanstream::rdbuf (C++23)

Underlying buffer operations

basic_ispanstream::span (C++23)

Non-member functions

swap(std::basic_ipanstream) (C++23)

 

std::span<const CharT> span() const noexcept;	(1)	(since C++23)
void span( std::span<CharT> s ) noexcept;	(2)	(since C++23)
template< class SpanLike > void span( SpanLike&& r ) noexcept;	(3)	(since C++23)

1) Gets a span referencing the written area if std::ios_base::out is set in the open mode of the wrapped std::basic_spanbuf, or a span referencing the underlying buffer otherwise.

2) Makes the wrapped std::basic_spanbuf perform I/O on the buffer referenced by s.

3) Same as (2), except that s is obtained as if by
std::span<const CharT> cs{std::forward<SpanLike>(r)};
std::span<CharT> s{const_cast<CharT*>(cs.data()), cs.size()};
. This overload participates in overload resolution only if SpanLike models borrowed_range, std::convertible_to<SpanLike, std::span<CharT>> is false, and std::convertible_to<SpanLike, std::span<const CharT>> is true.

Parameters

s	-	std::span referencing the storage to be use as the new underlying buffer of stream
r	-	borrowed_range to be use as the new underlying buffer of stream

Return value

1) A std::span referencing the underlying buffer or written area, depending on the open mode of the wrapped std::basic_spanbuf.

2,3) (none)

Example

Run this code

#include <cassert>
#include <iostream>
#include <span>
#include <spanstream>
 
int main()
{
    char out_buf[16];
    std::ospanstream ost{std::span<char>{out_buf}};
    ost << "C++" << ' ' << 23 << '\0'; // note explicit null-termination
    auto sp = ost.span();
    assert(
        sp[0] == 'C' && sp[1] == '+' && sp[2] == '+' &&
        sp[3] == ' ' && sp[4] == '2' && sp[5] == '3' &&
        sp[6] == '\0'
    );
    std::cout << "sp.data(): [" << sp.data() << "]\n";
    std::cout << "out_buf: [" << out_buf << "]\n";
    // spanstream uses out_buf as internal storage, no allocations
    assert(static_cast<char*>(out_buf) == sp.data());
 
    const char in_buf[] = "X Y 42";
    std::ispanstream ist{std::span<const char>{in_buf}};
    assert(static_cast<const char*>(in_buf) == ist.span().data());
    char c;
    ist >> c;
    assert(c == 'X');
    ist >> c;
    assert(c == 'Y');
    int i;
    ist >> i;
    assert(i == 42);
    ist >> i; // buffer is exhausted
    assert(!ist);
}

Output:

sp.data(): [C++ 23]
out_buf: [C++ 23]

See also

span	obtains or initializes an underlying buffer according to mode (public member function of std::basic_spanbuf<CharT,Traits>)