operator<<,>>(std::basic_string)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)   Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::starts_with (C++20)   basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23) basic_string::swap

Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos Deduction guides (C++17) Non-member functions operator+ swap(std::basic_string) operator""s (C++14) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) Numeric conversion stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string>hash<std::u8string> (C++11)  (C++11)(C++11)(C++11)(C++20) hash<std::pmr::string>hash<std::pmr::wstring>hash<std::pmr::u32string>hash<std::pmr::u16string>hash<std::pmr::u8string> (C++17)(C++17)(C++17)(C++17)(C++20)

 

Defined in header <string>
template< class CharT, class Traits, class Allocator > std::basic_ostream<CharT, Traits>&     operator<<( std::basic_ostream<CharT, Traits>& os,                 const std::basic_string<CharT, Traits, Allocator>& str );	(1)
template< class CharT, class Traits, class Allocator > std::basic_istream<CharT, Traits>&     operator>>( std::basic_istream<CharT, Traits>& is,                 std::basic_string<CharT, Traits, Allocator>& str );	(2)

1) Behaves as a FormattedOutputFunction. After constructing and checking the sentry object, determines the output format padding as follows:

a) If str.size() is not less than os.width(), uses the range [str.begin(), str.end()) as-is

b) Otherwise, if (os.flags() & ios_base::adjustfield) == ios_base::left, places os.width()-str.size() copies of the os.fill() character after the character sequence

c) Otherwise, places os.width()-str.size() copies of the os.fill() character before the character sequence.

Then stores each character from the resulting sequence (the contents of str plus padding) to the output stream os as if by calling os.rdbuf()->sputn(seq, n), where n=std::max(os.width(), str.size())

Finally, calls os.width(0) to cancel the effects of std::setw, if any.

2) Behaves as a FormattedInputFunction. After constructing and checking the sentry object, which may skip leading whitespace, first clears str with str.erase(), then reads characters from is and appends them to str as if by str.append(1, c), until one of the following conditions becomes true:

• N characters are read, where N is is.width() if is.width() > 0, otherwise N is str.max_size()
• the end-of-file condition occurs in the stream is
• std::isspace(c,is.getloc()) is true for the next character c in is (this whitespace character remains in the input stream).

If no characters are extracted then std::ios::failbit is set on is, which may throw std::ios_base::failure.

Finally, calls is.width(0) to cancel the effects of std::setw, if any.

Exceptions

1) may throw std::ios_base::failure if an exception is thrown during output.

2) may throw std::ios_base::failure if no characters are extracted from is (e.g the stream is at end of file, or consists of whitespace only), or if an exception is thrown during input.

Parameters

os	-	a character output stream
is	-	a character input stream
str	-	the string to be inserted or extracted

Return value

1) os

2) is

Example

Run this code

#include <iostream>
#include <string>
#include <sstream>
 
int main()
{
    std::string greeting = "Hello, whirled!";
    std::istringstream iss(greeting);
 
    std::string hello_comma, whirled, word;
 
    iss >> hello_comma;
    iss >> whirled;
 
    std::cout << greeting << '\n'
              << hello_comma << '\n' << whirled << '\n';
 
    //Reset the stream
    iss.clear();
    iss.seekg(0);
 
    while (iss >> word)
        std::cout << '+' << word << '\n';
}

Output:

Hello, whirled!
Hello,
whirled!
+Hello,
+whirled!

See also

operator<< (C++17)

performs stream output on string views (function template)