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Showing content from https://en.cppreference.com/w/cpp/language/../types/../string/basic_string/operator_ltltgtgt.html below:

operator<<,>>(std::basic_string) - cppreference.com

(1) (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.

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.

[edit] Exceptions 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.

[edit] Parameters os - a character output stream is - a character input stream str - the string to be inserted or extracted [edit] Return value

1) os

2) is

[edit] Example

#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!

[edit] 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 [edit] See also performs stream output on string views
(function template) [edit]

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