namespace std {
class ios_base::failure : public system_error {
public:
explicit failure(const string& msg, const error_code& ec = io_errc::stream);
explicit failure(const char* msg, const error_code& ec = io_errc::stream);
};
}
The class failure defines the base class for the types of all objects thrown as exceptions, by functions in the iostreams library, to report errors detected during stream buffer operations.
When throwing ios_base::failure exceptions, implementations should provide values of ec that identify the specific reason for the failure. [ Note: Errors arising from the operating system would typically be reported as system_category() errors with an error value of the error number reported by the operating system. Errors arising from within the stream library would typically be reported as error_code(io_errc::stream, iostream_category()). — end note ]
explicit failure(const string& msg, , const error_code& ec = io_errc::stream);
Effects: Constructs an object of class failure by constructing the base class with msg and ec.
explicit failure(const char* msg, const error_code& ec = io_errc::stream);
Effects: Constructs an object of class failure by constructing the base class with msg and ec.
The type fmtflags is a bitmask type ([bitmask.types]). Setting its elements has the effects indicated in Table [tab:iostreams.fmtflags.effects].
| Element | Effect(s) if set |
| boolalpha | insert and extract bool type in alphabetic format |
| dec | converts integer input or generates integer output in decimal base |
| fixed | generate floating-point output in fixed-point notation |
| hex | converts integer input or generates integer output in hexadecimal base |
| internal | adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated |
| left | adds fill characters on the right (final positions) of certain generated output |
| oct | converts integer input or generates integer output in octal base |
| right | adds fill characters on the left (initial positions) of certain generated output |
| scientific | generates floating-point output in scientific notation |
| showbase | generates a prefix indicating the numeric base of generated integer output |
| showpoint | generates a decimal-point character unconditionally in generated floating-point output |
| showpos | generates a + sign in non-negative generated numeric output |
| skipws | skips leading whitespace before certain input operations |
| unitbuf | flushes output after each output operation |
| uppercase | replaces certain lowercase letters with their uppercase equivalents in generated output |
Type fmtflags also defines the constants indicated in Table [tab:iostreams.fmtflags.constants].
| Constant | Allowable values |
| adjustfield | left | right | internal |
| basefield | dec | oct | hex |
| floatfield | scientific | fixed |
The type iostate is a bitmask type ([bitmask.types]) that contains the elements indicated in Table [tab:iostreams.iostate.effects].
| Element | Effect(s) if set |
| badbit | indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file); |
| 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. |
The type openmode is a bitmask type ([bitmask.types]). It contains the elements indicated in Table [tab:iostreams.openmode.effects].
| Element | Effect(s) if set |
| app | seek to end before each write |
| ate | open and seek to end immediately after opening |
| binary | perform input and output in binary mode (as opposed to text mode) |
| in | open for input |
| out | open for output |
| trunc | truncate an existing stream when opening |
The type seekdir is an enumerated type ([enumerated.types]) that contains the elements indicated in Table [tab:iostreams.seekdir.effects].
| Element | Meaning |
| beg | request a seek (for subsequent input or output) relative to the beginning of the stream |
| cur | request a seek relative to the current position within the sequence |
| end | request a seek relative to the current end of the sequence |
namespace std {
class ios_base::Init {
public:
Init();
~Init();
private:
static int init_cnt; // exposition only
};
}
The class Init describes an object whose construction ensures the construction of the eight objects declared in <iostream> ([iostream.objects]) that associate file stream buffers with the standard C streams provided for by the functions declared in <cstdio> ([c.files]).
For the sake of exposition, the maintained data is presented here as:
static int init_cnt, counts the number of constructor and destructor calls for class Init, initialized to zero.
Effects: Constructs an object of class Init. Constructs and initializes the objects cin, cout, cerr, clog, wcin, wcout, wcerr, and wclog if they have not already been constructed and initialized.