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 an FormattedOutputFunction
. After constructing and checking the sentry object, determines the output format padding as follows:
- a) If
str.size()
is not less thanos.width()
, uses the range[str.begin(), str.end())
as-is - b) Otherwise, if
(os.flags() & ios_base::adjustfield) == ios_base::left
, placesos.width()-str.size()
copies of theos.fill()
character after the character sequence - c) Otherwise, places
os.width()-str.size()
copies of theos.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 an 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, whereN
isis.width()
ifis.width() > 0
, otherwiseN
isstr.max_size()
- the end-of-file condition occurs in the stream
is
-
std::isspace(c,is.getloc())
is true for the next characterc
inis
(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 os.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
#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,
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