std::basic_istream<CharT,Traits>::operator>> - cppreference.com (original) (raw)

Extracts values from an input stream.

1-11) Extracts a value potentially skipping preceding whitespace. The value is stored to a given reference value.

1. Extracts a short value potentially skipping preceding whitespace. The value is stored to a given reference value.

2. Extracts an int value potentially skipping preceding whitespace. The value is stored to a given reference value.

3. Extracts an extended floating-point value potentially skipping preceding whitespace. The value is stored to a given reference value. The library provides overloads for all cv-unqualified extended floating-point types as the referenced type of the parameter value.

Determines the standard floating-point type FP as follows:

• If the floating-point conversion rank of /* extended-floating-point-type */ is less than or equal to that of float, then FP is float.
• Otherwise, if the floating-point conversion rank of /* extended-floating-point-type */ is less than or equal to that of double, then FP is double.
• Otherwise, FP is long double.

This function behaves as a FormattedInputFunction. After constructing and checking the sentry object, which may skip leading whitespace, extracts an FP value fval by calling

std::num_get::get()

. After that:

• If fval < -std::numeric_limits</* extended-floating-point-type */>::max(), sets failbit and stores -std::numeric_limits</* extended-floating-point-type */>::max() to val.
• Otherwise, if std::numeric_limits</* extended-floating-point-type */>::max() < fval, sets failbit and stores std::numeric_limits</* extended-floating-point-type */>::max() to val.
• Otherwise, stores static_cast</* extended-floating-point-type */>(fval) to val.

15-17) Calls func(*this), where func is an I/O manipulator.

1. Behaves as an UnformattedInputFunction. After constructing and checking the sentry object, extracts all data from *this and stores it to sb. The extraction stops if one of the following conditions are met:

• end-of-file occurs on the input sequence;
• inserting in the output sequence fails (in which case the character to be inserted is not extracted);
• an exception occurs (in which case the exception is caught, and only rethrown if it inserted no characters and failbit is enabled in exceptions()).

In either case, stores the number of characters extracted in the member variable accessed by subsequent calls to gcount(). If sb is a null pointer or if no characters were inserted into sb, calls setstate(failbit) (which may throw std::ios_base::failure if enabled).

If extraction fails (e.g. if a letter was entered where a digit is expected), zero is written to value and failbit is set. For signed integers, if extraction results in the value too large or too small to fit in value, std::numeric_limits<T>::max() or std::numeric_limits<T>::min() (respectively) is written and failbit flag is set. For unsigned integers, if extraction results in the value too large or too small to fit in value, std::numeric_limits<T>::max() is written and failbit flag is set.

[edit] Parameters

[edit] Return value

1-16,18) *this

1. func(*this)

[edit] Notes

For overload (14), when the extended floating-point type has a floating-point conversion rank that is not equal to the rank of any standard floating-point type, then double rounding during the conversion can result in inaccurate results. std::from_chars() can be used in situations where maximum accuracy is important.

[edit] Example

Output:

n = 41 f = 3.14 b = false hello world

[edit] Defect reports

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

[edit] See also