Library: Input/output
Does not inherit
Base class that defines member types and maintains data for classes that inherit from it
#include <ios>
namespace std {
class ios_base;
}
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
Arrays of user data used for storage management
A number of static constant data members
Additional information that is stored by the program for its private use
namespace std {
class ios_base {
public:
class failure;
typedef T1 fmtflags;
static const fmtflags boolalpha;
static const fmtflags dec;
static const fmtflags fixed;
static const fmtflags hex;
static const fmtflags internal;
static const fmtflags left;
static const fmtflags oct;
static const fmtflags right;
static const fmtflags scientific;
static const fmtflags showbase;
static const fmtflags showpoint;
static const fmtflags showpos;
static const fmtflags skipws;
static const fmtflags unitbuf;
static const fmtflags uppercase;
static const fmtflags adjustfield;
static const fmtflags basefield;
static const fmtflags floatfield;
typedef T2 iostate;
static const iostate badbit;
static const iostate eofbit;
static const iostate failbit;
static const iostate goodbit;
typedef T3 openmode;
static const openmode app;
static const openmode ate;
static const openmode binary;
static const openmode in;
static const openmode out;
static const openmode trunc;
static const openmode nocreate;
static const openmode noreplace;
enum T4 seekdir;
static const seekdir beg;
static const seekdir cur;
static const seekdir end;
class Init;
fmtflags flags () const;
fmtflags flags (fmtflags);
fmtflags setf (fmtflags);
fmtflags setf (fmtflags, fmtflags);
void unsetf (fmtflags);
streamsize precision () const;
streamsize precision (streamsize);
streamsize width () const;
streamsize width (streamsize);
locale imbue (const locale&);
locale getloc () const;
static int xalloc ();
long& iword (int);
void*& pword (int);
virtual ~ios_base();
enum event { erase_event, imbue_event, copyfmt_event };
typedef void (*event_callback)(event, ios_base&, int);
void register_callback (event_call_back, int);
static bool sync_with_stdio (bool = true);
protected:
ios_base();
};
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&);
}
fmtflags
The type fmtflags is a bitmask type. See Bitmask Type for more information. Setting its elements has the following effects:
showpos |
Generates a + sign in nonnegative 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. |
The following constants are also defined:
adjustfield |
left | right | internal |
basefield |
dec | hex | oct |
floatfield |
scientific | fixed |
iostate
The type iostate is a bitmask type. See Bitmask Types for more information. 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. |
goodbit |
Initial stream state, no other bit is set. |
openmode
The type openmode is a bitmask type. See Bitmask Types for more information. Setting its elements has the following effects:
app |
Attempts to seek to the end of the file immediately before each write. Each seek and the subsequent write are performed as a single atomic operation. |
ate |
Attempts to seek to the end of the file immediately after opening. The opening and the subsequent seek may be performed as two operations. |
binary |
Performs input and output in binary mode rather than text mode. In binary mode the stream treats the contents of the file as a sequence of bytes without interpreting in any special way, certain sequences of characters such as carriage returns and line feeds. |
in |
Opens for input. |
out |
Opens for output. |
trunc |
Attempts to truncate an existing file to 0 size immediately after opening. The file must be opened for output (i.e., with out). The opening and the subsequent truncation are performed as a single atomic operation. |
nocreate |
Successfully opens the file if and only if a file with that name already exists. The checking for the file's existence and its subsequent creation are performed as a single atomic operation. |
noreplace |
Successfully creates the file if and only if a file with that name does not already exist and the file is being opened for output (i.e., with out). The checking for the file's existence and its subsequent creation are performed as a single atomic operation. |
NOTE -- The nocreate and noreplace elements are not part of the C++ Standard, but are provided as an extension. See Appendix B, for a complete list of extensions of this implementation.
seekdir
The type seekdir is an enumerated 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
Constants of the enumerated type event are passed as arguments to user-defined callback functions registered with the stream objects via register_callback():
erase_event |
The stream object is being erased. |
imbue_event |
A new locale is being imbued in the stream object. |
copyfmt_event |
The copyfmt() member function has been called on an object. |
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.
ios_base();
The ios_base members have an indeterminate value after construction.
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.
fmtflags flags() const;
Returns the format control information for both input and output.
fmtflags flags(fmtflags fmtfl);
Sets flags() to fmtfl and returns the previous value of flags().
fmtflags setf(fmtflags fmtfl);
Sets flags() to (fmtfl | flags()) and returns the previous value of flags().
fmtflags setf(fmtflags fmtfl, fmtflags mask);
Clears mask in flags(), sets (fmtfl & mask) in flags(), and returns the previous value of flags().
void unsetf(fmtflags mask);
Clears mask in flags().
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.
long& iword(int idx);
If iarray is a null pointer, allocates an array of longs of sufficient size, and stores a pointer to its first element in iarray. The function then extends the array pointed to by iarray, as necessary, to include the element iarray[idx]. Each newly allocated element of the array is initialized to 0. The reference returned may become invalid after another call to the object's iword() member with a different index, after a call to its copyfmt() member, or when the object is destroyed. If the function fails, it sets failbit, which may throw an exception. On success, the function returns iarray[idx]; otherwise, a valid long& initialized to 0.
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);
If parray is a null pointer, allocates an array of void* of sufficient size, and stores a pointer to its first element in parray. The function then extends the array pointed at by parray, as necessary, to include the element parray[idx]. Each newly allocated element of the array is initialized to 0. The reference returned may become invalid after another call to the object's pword member with a different index, after a call to its copyfmt() member, or when the object is destroyed. If the function fails, it sets failbit, which may throw an exception. On success, the function returns parray[idx]; otherwise, a valid void*& initialized to 0.
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.
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.
streamsize width() const;
Returns the field width (number of characters) to generate on certain output conversions.
streamsize width(streamsize wide);
Saves the field width, 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.
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.
Constructor
explicit failure(const string& msg);
Constructs an object of class failure, initializing the base class with exception(msg).
Public Member Function
const char* what() const;
Returns the message msg with which the exception was created.
The class Init describes an object whose construction ensures the construction of the eight objects declared in <iostream>, which associates file stream buffers with the standard C streams.
The following functions are ios_base manipulators.
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.
basic_ios, basic_istream, basic_ostream, char_traits
ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 27.4.2