Description

When (out.flags() & std::ios_base::boolalpha) == 0, this function reads a long value from the input stream in and converts that value to a tribool. If that value is 0, x becomes false; if it is 1, x becomes true; if it is 2, becomes indetermine; otherwise, the operation fails (and the fail bit is set on the input stream in).

When (out.flags() & std::ios_base::boolalpha) != 0, this function first determines the names of the false, true, and indeterminate values. The false and true names are extracted from the std::numpunct facet of the input stream's locale (if the C++ standard library implementation supports locales), or from the default_false_name and default_true_name functions (if there is no locale support). The indeterminate name is extracted from the appropriate indeterminate_name facet (if it is available in the input stream's locale), or from the get_default_indeterminate_name function (if the C++ standard library implementation does not support locales, or the indeterminate_name facet is not specified for this locale object). The input is then matched to each of these names, and the tribool x is assigned the value corresponding to the longest name that matched. If no name is matched or all names are empty, the operation fails (and the fail bit is set on the input stream in).