Why Are Some C iomanip Manipulators Sticky While Others, Like `std::setw()`, Are Not?

Sticky Iomanip Manipulators

In C , iomanip manipulators are stream modifiers, used to alter the behavior or format of input and output streams. However, not all manipulators behave the same way; some are temporary and affect only the next insertion, while others are "sticky," remaining in effect until explicitly changed.

Why is std::setw() Non-Sticky?

Unlike most other manipulators, std::setw() does not alter the state of the stream permanently. This is because it is considered a formatting manipulator, where each insertion requires explicit width specification for proper alignment. By default, it resets to zero after each insertion to avoid ambiguity and maintain control over formatting.

Sticky Manipulators

The following manipulators are sticky, meaning they remain in effect until altered by another manipulator or explicitly reset:

• std::setiosflags
• std::resetiosflags
• std::setbase
• std::setfill
• std::setprecision
• All flag-modifying manipulators (e.g., std::boolalpha, std::showbase)
• All formatting manipulators (e.g., std::fixed, std::internal)
• All stream state modifiers (e.g., std::ws, std::endl)

std::ios_base::width() vs. std::setw()

std::ios_base::width() is a member function of std::ios_base, the base class of all stream types. It returns the current width of the field. However, it does not directly control the field width; std::setw() must be used to set the field width.

Online Reference

Refer to the C Standard Library documentation for a comprehensive list of iomanip manipulators and their behavior. It provides detailed descriptions and examples of their functionality. Alternatively, online resources like the cppreference website offer thorough information on manipulators, including their sticky nature.

The above is the detailed content of Why Are Some C iomanip Manipulators Sticky While Others, Like `std::setw()`, Are Not?. For more information, please follow other related articles on the PHP Chinese website!