C++ named requirements: UnformattedInputFunction
Requirements
An UnformattedInputFunction is a stream input function that performs the following:
-
Constructs an object of type basic_istream::sentry with automatic storage duration and with the noskipws argument set to true, which performs the following:
- If eofbit or badbit are set on the input stream, sets the failbit as well,
and if exceptions on failbit are enabled in this input stream's exception mask
((exceptions() & failbit) != 0)
, throws ios_base::failure. - Flushes the tie()'d output stream, if applicable.
- If eofbit or badbit are set on the input stream, sets the failbit as well,
and if exceptions on failbit are enabled in this input stream's exception mask
-
Checks the status of the sentry by calling sentry::operator bool(), which is equivalent to basic_ios::good.
- If the operator returns
false
or sentry's constructor throws an exception:- Sets the number of extracted characters (gcount) in the input stream to zero.
- If the function was called to write to an array of CharT, writes CharT() (the null character) to the first location of the array.
- If the operator returns true, performs the input as if by calling
rdbuf()->sbumpc()
orrdbuf()->sgetc()
.- If the end of the stream is reached (the call to
rdbuf()->sbumpc()
orrdbuf()->sgetc()
returnsTraits::eof()
), sets eofbit. If exceptions on eofbit are enabled in this stream's exception mask((exceptions() & eofbit) != 0
), throws ios_base::failure. - If an exception is thrown during input, sets badbit in the input stream.
If exceptions on badbit are enabled in this stream's exception mask
((exceptions() & badbit) != 0
), the exception is also rethrown.- Exceptions thrown from basic_ios::clear are not caught or rethrown.
- If no exception was thrown during input, sets the number of extracted characters (gcount) in the input stream.
- If the end of the stream is reached (the call to
- If the operator returns
-
In any event, whether terminating by exception or returning, the sentry's destructor is called before leaving this function.
Standard library
The following standard library functions are UnformattedInputFunctions.
- std::getline, except that it does not modify gcount.
- basic_istream::operator>>(basic_streambuf*)
- basic_istream::get
- basic_istream::getline
- basic_istream::ignore
- basic_istream::peek
- basic_istream::read
- basic_istream::readsome
- basic_istream::putback, except that it first clears eofbit
- basic_istream::unget, except that it first clears eofbit
- basic_istream::sync, except that it does not modify gcount
- basic_istream::tellg, except that it does not modify gcount
- basic_istream::seekg, except that it first clears eofbit and does not modify gcount
- std::ws, except that it does not modify gcount
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 61 | C++98 | it was unclear whether throwing an exception because of setting eofbit and/or failbit will result in setting badbit | exceptions thrown from basic_ios::clear are not caught or rethrown |
LWG 160 | C++98 | the process of determining whether the exception caught is rethrown mentioned a non-existing function exception() | corrected to exceptions() |
LWG 243 | C++98 | the behavior when sentry::operator bool() returns false or the sentry object fails to be constructed was not specified | specified |