## ios_base

    Base Class

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Interface
- Types
- Public Constructors
- Public Destructors
- Public Member Functions
- Class failure
- Class Init
- Non-member Functions
- See Also
- Standards Conformance

### Summary

Defines member types and maintains data for classes that inherit from it.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

Data Types
event_callback fmtflags iostate openmode | seekdir

Member Functions
boolalpha() copyfmt() dec() failure() fixed() flags() getloc() hex() imbue() internal() | is_sync() iword() left() noboolalpha() noshowbase() noshowpoint() noshowpos() noskipws() nounitbuf() nouppercase() | oct() precision() pword() register_callback() right() scientific() setf() showbase() showpoint() showpos() | skipws() sync_with_stdio() unitbuf() unsetf() uppercase() what() width() xalloc()

### Synopsis

    #include <ios>
    class ios_base;

### Description

The class ios_base defines several member types:

- A class `failure` derived from `exception`.

- A class `Init.`

- Three bitmask types: `fmtflags`, `iostate`, and `openmode.`

- Two enumerated types: `seekdir` and `event.`

It maintains several kinds of data:

- Control information that influences how to interpret (format) input sequences and how to generate (format) output sequences.

- Locale object used within the stream classes.

- Additional information that is stored by the program for its private use.

### Interface

    class ios_base {

     public:

       class failure : public exception {

          public:

              explicit failure(const string& msg);
              virtual ~failure() throw();
              virtual const char* what() const throw();
        };

       typedef int      fmtflags;

       enum fmt_flags {
                        boolalpha   = 0x0001,
                        dec         = 0x0002,
                        fixed       = 0x0004,
                        hex         = 0x0008,
                        internal    = 0x0010,
                        left        = 0x0020,
                        oct         = 0x0040,
                        right       = 0x0080,
                        scientific  = 0x0100,
                        showbase    = 0x0200,
                        showpoint   = 0x0400,
                        showpos     = 0x0800,
                        skipws      = 0x1000,
                        unitbuf     = 0x2000,
                        uppercase   = 0x4000,
                        adjustfield = left | right | internal,
                        basefield   = dec | oct | hex,
                        floatfield  = scientific | fixed
                      };

       typedef int      iostate;

       enum io_state {
                       goodbit     = 0x00,
                       badbit      = 0x01,
                       eofbit      = 0x02,
                       failbit     = 0x04
                     };

       typedef int      openmode;

       enum open_mode {
                        app         = 0x01,
                        binary      = 0x02,
                        in          = 0x04,
                        out         = 0x08,
                        trunc       = 0x10,
                        ate         = 0x20
                      };

       typedef int      seekdir;

       enum seek_dir {
                         beg         = 0x0,
                         cur         = 0x1,
                         end         = 0x2
                     };

       class Init;

       fmtflags flags() const;
       fmtflags flags(fmtflags fmtfl);
       fmtflags setf(fmtflags fmtfl);
       fmtflags setf(fmtflags fmtfl, fmtflags mask);
       void unsetf(fmtflags mask);

       streamsize precision() const;
       streamsize precision(streamsize prec);
       streamsize width() const;
       streamsize width(streamsize wide);

       locale imbue(const locale& loc);
       locale getloc() const

       static int xalloc();
       long&  iword(int index);
       void*& pword(int index);

       ios_base& copyfmt(const ios_base& rhs);

       enum event     {
                        erase_event   = 0x0001,
                        imbue_event   = 0x0002,
                        copyfmt_event = 0x004
                      };

       typedef void (*event_callback) (event, ios_base&,
                     int index);
       void register_callback(event_callback fn, int index);

       bool synch_with_stdio(bool sync = true);
       bool is_synch();

      protected:

       ios_base();
       virtual ~ios_base();

      private:

       union ios_user_union {
                               long  lword;
                               void* pword;
                            };

       union ios_user_union *userwords_;
    };

     ios_base& boolalpha(ios_base&);
     ios_base& noboolalpha(ios_base&);
     ios_base& showbase(ios_base&);
     ios_base& noshowbase(ios_base&);
     ios_base& showpoint(ios_base&);
     ios_base& noshowpoint(ios_base&);
     ios_base& showpos(ios_base&);
     ios_base& noshowpos(ios_base&);
     ios_base& skipws(ios_base&);
     ios_base& noskipws(ios_base&);
     ios_base& uppercase(ios_base&);
     ios_base& nouppercase(ios_base&);
     ios_base& internal(ios_base&);
     ios_base& left(ios_base&);
     ios_base& right(ios_base&);
     ios_base& dec(ios_base&);
     ios_base& hex(ios_base&);
     ios_base& oct(ios_base&);
     ios_base& fixed(ios_base&);
     ios_base& scientific(ios_base&);
     ios_base& unitbuf(ios_base&);
     ios_base& nounitbuf(ios_base&);

### Types

    fmtflags

The type `fmtflags` is a bitmask type. Setting its elements has the following effects:

`showpos` `` | Generates a + sign in non-negative generated numeric output.
`showbase` `` | Generates a prefix indicating the numeric base of generated integer output
`uppercase` `` | Replaces certain lowercase letters with their uppercase equivalents in generated output
`showpoint` `` | Generates a decimal-point character unconditionally in generated floating-point output
`boolalpha` `` | Inserts and extracts bool type in alphabetic format
`unitbuf` `` | Flushes output after each output operation
`internal` `` | Adds fill characters at a designated internal point in certain generated output. If no such point is designated, it's identical to `right`.
`left` `` | Adds fill characters on the right (final positions) of certain generated output
`right` `` | Adds fill characters on the left (initial positions) of certain generated output
`dec` `` | Converts integer input or generates integer output in decimal base
`hex` `` | Converts integer input or generates integer output in hexadecimal base
`oct` `` | Converts integer input or generates integer output in octal base
`fixed` `` | Generates floating-point output in fixed-point notation
`scientific` `` | Generates floating-point output in scientific notation
`skipws` | Skips leading white space before certain input operation.

    iostate

The type `iostate` is a bitmask type. Setting its elements has the following effects:

`badbit` | Indicates a loss of integrity in an input or output sequence.
`eofbit` | Indicates that an input operation reached the end of an input sequence.
`failbit` | Indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.

    openmode

The type `openmode` is a bitmask type. Setting its elements has the following effects:

`app` | Seeks to the end before writing.
`ate` | Opens and seeks to the end immediately after opening.
`binary` | Performs input and output in binary mode.
`in` | Opens for input.
`out` | Opens for output.
`trunc` | Truncates an existing stream when opening.

    seekdir

The type `seekdir` is a bitmask type. Setting its elements has the following effects:

`beg` | Requests a seek relative to the beginning of the stream.
`cur` | Requests a seek relative to the current position within the sequence.
`end` | Requests a seek relative to the current end of the sequence.

    event_callback

The type `event_callback` is the type of the callback function used as a parameter in the function `register_callback`. These functions allow you to use the `iword`, `pword` mechanism in an exception-safe environment.

### Public Constructors

    ios_base();

The `ios_base` members have an indeterminate value after construction.

### Public Destructors

    virtual
     ~ios_base();

Destroys an object of class `ios_base`. Calls each registered callback pair `(fn, index)` as `(*fn)(erase_event,*this, index)` at such a time that any `ios_base` member function called from within `fn` has well-defined results.

### Public Member Functions

    ios_base&
    copyfmt(const ios_base& rhs);

Assigns to the member objects of `*this` the corresponding member objects of `rhs`. The contents of the union pointed to by `pword` and `iword` are copied, not the pointers themselves. Before copying any part of `rhs`, calls each registered callback pair `(fn,index)` as `(*fn)(erase_even,*this, index)`. After all parts have been replaced, calls each callback pair that was copied from `rhs` as `(*fn)(copy_event,*this,index)`.

    fmtflags
    flags() const;

Returns the format control information for both input and output.

    fmtflags
    flags(fmtflags fmtfl);

Saves the format control information, then sets it to `fmtfl` and returns the previously saved value.

    locale
    getloc() const;

Returns the imbued locale, which is used to perform locale-dependent input and output operations. The default locale, `locale::locale()`, is used if no other locale object has been imbued in the stream by a call to the `imbue` function.

    locale
    imbue(const locale& loc);

Saves the value returned by `getloc()`, then assigns `loc` to a private variable and calls each registered callback pair `(fn, index)` as `(*fn)(imbue_event,*this, index)`. It then returns the previously saved value.

    bool
    is_sync();

Returns `true` if the C++ standard streams and the standard C streams are synchronized. Otherwise returns `false`. This function is not part of the C++ standard.

    long&
    iword(int idx);

Returns `userwords_[idx].iword`. If `userwords_` is a null pointer, allocates a union of `long` and `void*` of unspecified size and stores a pointer to its first element in `userwords_`. The function then extends the union pointed to by `userwords_` to include the element `userwords_[idx]`. Each newly allocated element of the union is initialized to zero. The reference returned may become invalid after another call to the object's `iword` or `pword` member with a different index, after a call to its `copyfmt` member, or when the object is destroyed.

    streamsize
    precision() const;

Returns the precision (number of digits after the decimal point) to generate on certain output conversions.

    streamsize
    precision(streamsize prec);

Saves the precision, then sets it to `prec` and returns the previously saved value.

    void*&
    pword(int idx);

Returns `userword_[idx].pword`. If `userwords_` is a null pointer, allocates a union of `long` and `void*` of unspecified size and stores a pointer to its first element in `userwords_`. The function then extends the union pointed to by `userwords_` to include the element `userwords_[idx]`. Each newly allocated element of the array is initialized to zero. The reference returned may become invalid after another call to the object's `pword` or `iword` member with a different index, after a call to its `copyfmt` member, or when the object is destroyed.

    void
    register_callback(event_callback fn, int index);

Registers the pair `(fn, index)` such that during calls to `imbue()`, `copyfmt()`, or `~ios_base()`, the function `fn` is called with argument `index`. Functions registered are called when an event occurs, in opposite order of registration. Functions registered while a callback function is active are not called until the next event. Identical pairs are not merged; a function registered twice is called twice per event.

    fmtflags
    setf(fmtflags fmtfl);

Saves the format control information, then sets it to `fmtfl` and returns the previously saved value.

    fmtflags
    setf(fmtflags fmtfl, fmtflags mask);

Saves the format control information, then clears `mask` in `flags()`, sets `fmtfl & mask in flags()` and returns the previously saved value.

    bool
    sync_with_stdio(bool sync = true);

When called with a `false` argument, allows the C++ standard streams to operate independently of the standard C streams, which greatly improves performance. When called with a `true` argument, restores the default synchronization. The return value of the function is the status of the synchronization at the time of the call.

    void
    unsetf(fmtflags mask);

Clears `mask` in `flags()`.

    streamsize
    width() const;

Returns the field width (number of characters) to generate on certain output conversions.

    streamsize
    width(streamsize wide);

Saves the field width, then sets it to `wide` and returns the previously saved value.

    static int
    xalloc();

Returns the next static index that can be used with `pword` and `iword`. This is useful if you want to share data between several stream objects.

### Class failure

The class failure defines the base class for the types of all objects thrown as exceptions by functions in the iostreams library. It reports errors detected during stream buffer operations.

    explicit failure(const string& msg);

Constructs an object of class `failure`, initializing the base class with `exception(msg).`

    const char*
    what() const;

Returns the message `msg` with which the exception was created.

### Class Init

The class Init describes an object whose construction ensures the construction of the eight objects declared in `<iostream>`, which associate file stream buffers with the standard C streams.

### Non-member Functions

    ios_base&
    boolalpha(ios_base& str);

Calls `str.setf(ios_base::boolalpha)` and returns `str.`

    ios_base&
    dec(ios_base& str);

Calls `str.setf(ios_base::dec, ios_base::basefield)` and returns `str`.

    ios_base&
    fixed(ios_base& str);

Calls `str.setf(ios_base::fixed, ios_base::floatfield)` and returns `str`.

    ios_base&
    hex(ios_base& str);

Calls `str.setf(ios_base::hex, ios_base::basefield)` and returns `str`.

    ios_base&
    internal(ios_base& str);

Calls `str.setf(ios_base::internal, ios_base::adjustfield)` and returns `str`.

    ios_base&
    left(ios_base& str);

Calls `str.setf(ios_base::left, ios_base::adjustfield)` and returns `str`.

    ios_base&
    noboolalpha(ios_base& str);

Calls `str.unsetf(ios_base::boolalpha)` and returns `str.`

    ios_base&
    noshowbase(ios_base& str);

Calls `str.unsetf(ios_base::showbase)` and returns `str`.

    ios_base&
    noshowpoint(ios_base& str);

Calls `str.unsetf(ios_base::showpoint)` and returns `str`.

    ios_base&
    noshowpos(ios_base& str);

Calls `str.unsetf(ios_base::showpos)` and returns `str`.

    ios_base&
    noskipws(ios_base& str);

Calls `str.unsetf(ios_base::skipws)` and returns `str`.

    ios_base&
    nounitbuf(ios_base& str);

Calls `str.unsetf(ios_base::unitbuf)` and returns `str`.

    ios_base&
    nouppercase(ios_base& str);

Calls `str.unsetf(ios_base::uppercase)` and returns `str`.

    ios_base&
    oct(ios_base& str);

Calls `str.setf(ios_base::oct, ios_base::basefield)` and returns `str`.

    ios_base&
    right(ios_base& str);

Calls `str.setf(ios_base::right, ios_base::adjustfield)` and returns `str`.

    ios_base&
    scientific(ios_base& str);

Calls `str.setf(ios_base::scientific, ios_base::floatfield)` and returns `str`.

    ios_base&
    showbase(ios_base& str);

Calls `str.setf(ios_base::showbase)` and returns `str`.

    ios_base&
    showpoint(ios_base& str);

Calls `str.setf(ios_base::showpoint)` and returns `str`.

    ios_base&
    showpos(ios_base& str);

Calls `str.setf(ios_base::showpos)` and returns `str`.

    ios_base&
    skipws(ios_base& str);

Calls `str.setf(ios_base::skipws)` and returns `str`.

    ios_base&
    unitbuf(ios_base& str);

Calls `str.setf(ios_base::unitbuf)` and returns `str`.

    ios_base&
    uppercase(ios_base& str);

Calls `str.setf(ios_base::uppercase)` and returns `str`.

### See Also

basic_ios(3C++), basic_istream(3C++), basic_ostream(3C++), char_traits(3C++)

Working Paper for Draft Proposed International Standard for Information Systems--Programming Language C++, Section 27.4.2

### Standards Conformance

ANSI X3J16/ISO WG21 Joint C++ Committee

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998