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

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 is(greeting);
    std::string hello_comma;
    is >> hello_comma;
    std::cout << greeting << '\n' << hello_comma << '\n';
}

Output:

Hello, whirled!
Hello,

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

Null-terminated strings
Byte strings
Multibyte strings
Wide strings
Classes
basic_string
basic_string_view (C++17)
char_traits