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

 

C++

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Feature test macros(C++20)

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Technical specifications

Symbols index

External libraries

 

Strings library

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23)   basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) 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) 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

Modifiers basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)  basic_string::swap Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Operations basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr

Constants basic_string::npos Non-member functions operator+ swap(std::basic_string) 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 conversions 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) Literals operator""s (C++14) Helper classes hash<std::basic_string> (C++11) Deduction guides(C++17)

 

Defined in header <string>
template<class CharT, class Traits, class Allocator > std::basic_ostream<CharT, Traits>&     operator<<(std::basic_ostream<CharT, Traits>& os,                 conststd::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.

Then inserts each character from the resulting sequence seq (the contents of str plus padding) to the output stream os as if by calling os.rdbuf()->sputn(seq, n), where n is std::max(os.width(), str.size()) Finally, calls os.width(0) to cancel the effects of std::setw, if any.

Equivalent to return os <<std::basic_string_view<CharT, Traits>(str);.

(since C++17)

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, or
• 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 <sstream>#include <string>   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!

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 25	C++98	n was the smaller of os.width() and str.size()	n is the larger of them
LWG 90	C++98	std::isspace(c, getloc()) was used to check for spaces, but getloc is not declared in <string>	replaced getloc() with is.getloc()
LWG 91	C++98	operator>> did not behave as a FormattedInputFunction	behaves as a FormattedInputFunction
LWG 211	C++98	operator>> did not set failbit if no character is extracted	sets failbit
LWG 435	C++98	characters were inserted by os.rdbuf()->sputn(str.data(), n), and the resolution of LWG issue 25 made the behavior undefined if os.width() is larger than str.size()	determines the padding first and inserts the padded character sequence instead
LWG 586	C++98	operator<< did not behave as a FormattedOutputFunction	behaves as a FormattedOutputFunction

See also

operator<< (C++17)

performs stream output on string views (function template)