C++ Library - <ios_base>


Base class for the entire hierarchy of stream classes in the standard input/output library, describing the most basic part of a stream which is common to all stream objects, independently of their character type.

It has no public constructors, and thus no objects of this class can be declared. Both ios_base and its derived class basic_ios define the components of streams that do not depend on whether the stream is an input or an output stream: ios_base describes the members that are independent of the template parameters (i.e. the character type and traits), while basic_ios describes the members that do depend on them.

More specifically, the ios_base class maintains the following information of a stream −

field member functions description
Formatting format flags




A set of internal flags that affect how certain input/output operations are interpreted or generated. See member type fmtflags.
field width width Width of the next formatted element to insert.
display precision precision Decimal precision for the next floating-point value inserted.



The locale object used by the function for formatted input/output operations affected by localization properties.
Other callback stack register_callback Stack of pointers to functions that are called when certain events occur.
extensible arrays




Internal arrays to store objects of type long and void*.


Below is definition of ios_base as shown below −

class ios_base;

Member types

Sr.No. Member types Definition
1 event Type to indicate event type
2 event_callback Event callback function type
3 fmtflags Type for stream format flags
4 iostate Type for stream state flags
5 openmode Type for stream opening mode flags
6 seekdir Type for stream seeking direction flag

Public Member Functions

Sr.No. Member types Definition
1 (constructor) Construct object (public member function )
2 (destructor) Destruct object (public member function )


Sr.No. Member types Definition
1 flags It is used to get/set format flags
2 setf It is used to set specific format flags
3 unsetf It is used to clear specific format flags
4 precision It is used to get/Set floating-point decimal precision
5 width It is used to get/set field width


Sr.No. Member types Definition
1 imbue Imbue locale
2 getloc Get current locale

Internal extensible array

Sr.No. Member types Definition
1 xalloc It is used to get new index for extensible array [static]
2 iword It is used to get integer element of extensible array
3 pword It is used to get pointer element of extensible array


Sr.No. Member types Definition
1 register_callback Register event callback function
2 sync_with_stdio Toggle synchronization with cstdio streams [static]