I'm quite sure there will be some who will ask "Why did you build this ?". Yes, it is slower than printf and a little fatter than STL wcout, but...
There are two major reasons I built this template class, apart from the learning experience.
On the one hand I find the STL manipulators to be cumbersome, on the other,
the printf family of functions have a major drawback, they don't allow arbitrary
growth of the output string.
I could have wrapped only the ostrstream class but that would have
unnecessarily limited the use of this template for other kinds of output, namely
file and console.
The main template class, basic_oformatstream, acts as a shim ("something thin placed between two
parts to make a fit") between the user and the ostream the object is
tied to.
WARNING: There is a bug in the VC++ 6.0 STL implementation from Dinkumware.
See the end of file oformatstream.cpp for a short description of the bug (with code). An initial fix is to make the buffer size much larger in <xlocnum> template
num_putfunctionsvirtual _OI do_put(_OI _F, ios_base& _X, _E _Fill, double _V) constandvirtual _OI do_put(_OI _F, ios_base& _X, _E _Fill, long double _V) const. If making this kind of change to a standard template library file fills you with dread, I don't blame you, so if you can't or won't fix this then never ever try to output a really big floating point value without using the scientific format, ie. %e or %g, the other one %f could cause you grief.
So how do you use it ?
First construct an oformatstream by giving it a format and an output stream to write
to. Then it is just a matter of outputting values to the resulting oformatstream.
The order in which you send the output values is, as you
should expect, utterly dependent upon the order that you specify in the format
string.
You can change the format string by using the reformat manipulator which
takes a basic_formatter object as it's argument.
formatter f("%8d %6.2f"); oformatstream ofs("%8x %5.3e",&std::cout); ofs << reformat(f);
Note that formatter and oformatstream are typedefs
similar in purpose to those done for cout and wcout. In case you were wondering,
woformatstream and wformatter are the wide equivalents.
// Example usage: // // First a really simple situation: oformatstream ofs("[%s] [%8d] [%6.5f]\n", &std::cout); ofs << "example" << 1 << 3.141592 << setformat; // Note setformat is used to make sure the last field is output. // The last field ? Yes the "]\n" text. // You could also drop the '\n' and use the endl inserter instead. // This would result in the following code. oformatstream ofs("[%s] [%8d] [%6.5f]", &std::cout); ofs << "example" << 1 << 3.141592 << setformat << endl; // A slightly more complex example: // Set up a custom default format specification first format_specification fs(12 /*width*/,2/*precision*/,std::ios_base::dec); // Generate a formatter with this default format specification formatter format("[%s] [%d] [%f]", fs); // Construct the oformatstream with this custom formatter oformatstream ofs(format, &std::cout); ofs << "example" << 1 << 3.141592 << endl;
For some really complex examples see TestFormat.cpp in the demo
The following are more detailed descriptions of the template classes and the various implementation classes and functions you will find if you dig around inside oformatstream.hpp
The default constructor. Will require a call to tie() before output will workbasic_oformatstream()
Use a format string to construct the internal format
field vectorbasic_oformatstream(const std::basic_string<_E,_Tr>& s, _Myostream
*os = NULL)
Use a preconstructed basic_formatter which allows for a
custom default format specificationbasic_oformatstream(const basic_formatter<_E>& f, _Myostream *os =
NULL)
Inserter operators_Myt& operator<<(T) for T= {bool,int,long,...etc.}
Sets the internal formattervoid formatter(constbasic_formatter<_E,_Tr>& f)
Returns the internal formatterbasic_formatter<_E>& formatter()
Ties to an output streamvoid tie(_Myostream *os)
Returns the tied output stream_Myostream* get_ostream()
Sets the default format specificationvoid default_format_specification(const format_specification& f)
Returns the default format specificationformat_specification default_format_specification()
plus several others which are used internally but need to be public
The default constructorbasic_formatter()
Supply a default format specificationbasic_formatter(const format_specification fs)
Use a format stringbasic_formatter(std::basic_string<_E,_Tr> fs)
Use a format string and supply a default format specificationbasic_formatter(std::basic_string<_E,_Tr> s, const format_specification& fs)
format_flags
Manages changes to a std::ios_base::fmtflags value. Enforces
restrictions such as hex,dec and oct being mutually exclusive flags.
Provides operators |=, &=, = and various constructors and conversion
operators.
format_specification
A single field's format specification corresponds to a single field ie. "%7.5f"
TEMPLATE CLASS format_characters
Provides
a central place for storing constants required by the parsing routines.
Currently _E may be either char or wchar_t.
TEMPLATE CLASS basic_formatterfield
Holds the final results of parsing a single field's format specification. These being a prefix text string and format specification for the field.
TEMPLATE CLASS FormatFieldVector
derived from std::vector< basic_formatterfield<_E,_Tr>>
std::ios_base::fmtflags format_flag_from_char<_E>(const _E ch)
Converts the type character [cdefgisx] into appropriate ios_base flag values.
bool parse_format_specification<_E>( std::basic_string<_E>::const_iterator& it, std::basic_string<_E>::const_iterator& end, format_specification& outfs, bool& widthset, bool& precset, _E& fillchar)
Called by parse_field<_E>() to process a single field's format
specification. ie. everything after the percent (%) symbol.
bool parse_field <_E>( std::basic_string<_E>::const_iterator& it, std::basic_string<_E>::const_iterator& end, basic_formatterfield<_E>& outff, format_specification& default_fs)
Called by parse_format<_E> to process a format field. ie. The
prefix text followed by a format specification. Calls parse_format_specification<_E>()
bool parse_format<_E>( std::basic_string<_E>fs, FormatFieldVector<_E>& ffv, format_specification& default_fs)
Used by basic_formatter<_E> constructors to process a full format
specification. Calls parse_field<_E>() to build a
basic_formatterfield which it then stores in a FormatFieldVector.
TEMPLATE CLASS basic_formatter
The format of each field is controlled by the given format string.
TEMPLATE CLASS basic_oformatstream
Outputs values to the connected stream (does nothing if not). The internal basic_formatter object controls the layout of each output field and the order that they are expected. No exceptions are thrown if the supplied field type does not match the expected format. The output will probably just look awful.
I have also included StrENUM.h which is a collection
of macros to make nice little enumeration to string converter
functions.
Here is an example of it's use.
In a .cpp file
// Declares StrIOS_BASE_FORMAT_FLAGS() BEGIN_STR_ENUM_FUNC( IOS_BASE_FLAGS ) STR_ENUM_FLAG( std::ios_base::uppercase ) STR_ENUM_FLAG( std::ios_base::showbase ) STR_ENUM_FLAG( std::ios_base::showpoint ) STR_ENUM_FLAG( std::ios_base::showpos ) STR_ENUM_FLAG( std::ios_base::left ) STR_ENUM_FLAG( std::ios_base::right ) STR_ENUM_FLAG( std::ios_base::internal ) STR_ENUM_FLAG( std::ios_base::dec ) STR_ENUM_FLAG( std::ios_base::oct ) STR_ENUM_FLAG( std::ios_base::hex ) STR_ENUM_FLAG( std::ios_base::scientific ) STR_ENUM_FLAG( std::ios_base::fixed ) STR_ENUM_FLAG( std::ios_base::boolalpha ) STR_ENUM_FLAG( std::ios_base::skipws ) STR_ENUM_FLAG( std::ios_base::unitbuf ) END_STR_ENUM_FUNC
and in the calling source file
#include "StrENUM.h" typedef std::ios_base::_Fmtflags IOS_BASE_FLAGS; DECLARE_STR_ENUM_FUNC( IOS_BASE_FLAGS ); //
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Thanks for posting.