Which C Stream Manipulators are Sticky, and Why Isn't `setw()`?

Sticky Manipulators in C

In C programming, manipulators are used to modify the output formatting of streams. Certain manipulators behave in a "sticky" manner, meaning that their effects persist until explicitly changed.

Why is setw() not Sticky?

std::setw() is an example of a non-sticky manipulator. This means that it only affects the next insertion operation. After setw() is used, the width setting is reset to its default value.

Are any other Manipulators Sticky?

All manipulators except setw() are sticky. This includes:

• setiosflags
• resetiosflags
• setbase
• setfill
• setprecision
• setiosflags
• resetiosflags
• setbase
• setfill
• setprecision
• [no]boolalpha
• [no]showbase
• [no]showpoint
• [no]showpos
• [no]skipws
• [no]unitbuf
• [no]uppercase
• dec/ hex/ oct
• fixed/ scientific
• internal/ left/ right
• ws/ endl/ ends/ flush

Difference between std::ios_base::width() and std::setw()

std::setw() returns an object that represents a width value. This object can be used to set the width of the next item that is inserted into a stream.

std::ios_base::width() directly sets the width of the stream. Any subsequent insertions into the stream will be formatted with the new width.

Online Reference

Unfortunately, there is no clear documentation that explicitly states the sticky behavior of manipulators. However, the behavior can be inferred from the C Standard Library documentation.

Example of Sticky Manipulators

The following code demonstrates the sticky behavior of manipulators:

#include <iostream>
#include <iomanip>

using namespace std;

int main() {
  // Set the precision to 2 decimal places
  cout << setprecision(2);

  // Insert a number
  cout << 3.14 << endl;  // Output: 3.14

  // The precision is still set to 2 decimal places
  cout << 1.2345 << endl; // Output: 1.23
}

Conclusion

Sticky manipulators are a useful feature in C that can help control the formatting of output. However, it is important to be aware of their behavior to avoid unexpected results.

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