ecl_formatters Documentation

ecl_formatters

The formatters here simply format various input types to a specified text format. They can be used with most streaming types (including both ecl and stl streams).

Embedded Control Library

The formatters here simply format various input types to a specified text format. If you wish to just do fast type to text conversion without formatting, use the converters supplied in ecl_utilities.

History

    Type to text formatting is usually bundled with both streaming and
    device manipulation. Although this makes it very simple to do the
    most basic of type formatting, it also has the unfortunate consequence
    in that the formatter types (printf, sprintf, iostreams) are very
    heavyweight and subsequently slow. Especially for a simple task, they
    bring a sledge hammer when all that is needed is a gentle push.

    What the formatters attempt to do is to split the functionality
    of formatting from the concepts of device manipulation,
    streaming. This ensures that any simple task is not overdone with a
    heavyweight object (really important for logging) and it greatly enhances
    the efficiency and speed. The classes here also bring in type safety,
    something which is not guaranteed by either printf or sprintf.

Compiling & Linking

    Include the following at the top of any translation unit which
    requires this library:
// The formatter template family
// Common formatter parameters
// Integral formatter parameters
using ecl::Bin;
using ecl::Dec;
using ecl::Hex;
// Float formatter parameters
using ecl::Fixed;
using ecl::Sci;

You will also need to link to -lecl_formatters.

Usage

Instantiation

            Formatters are functors - functions with state. You instantiate a formatter
            type and then make use of it as if it were a function call.
Format<int> format(); // Default format initialisation
Format<int> format(8,RightAlign,Hex); // Custom format initialisation

Changing the Format Parameters

            The format parameters can be changed singly with appropriately named
            setters, or collectively via:: a bundled operator () call. Sometimes
            common combinations are also provided with a convenient setter via the operator ().
format.base(Hex)
format(8,RightAlign,Dec)

Changing the format parameters in this way will set the default formatting for any input values given to the formatter in the future.

Streaming

            The formatters are primarily intended to be used with streams. For convenience
            they have been designed to be used with any stream that implemenents the
            << operator. Subsequently they are useful with either TextStreams (ECL-IO) or
            the usual c++ streams. When used in conjunction with TextStreams they provide
            a very fast streaming interface.

Permanent Formatting

            To format with the parameters stored in the formatter, you simply
            provide the formatter with the input value. Note that the formatter will
            only accept a value of the type specified in the formatter's template
            argument.
ostream << format(i) << " " << format(9);

For convenience, you can also change the format parameter on the fly (this is recorded permanently).

ostream << format.base(Hex)(i) << " " << format(10,LeftAlign,Dec)(9);

Temporary Formatting

            Occasionally you will only need to change the format for one instance.
            To effect a temporary change in this way, supply the input value
            along with the specified formatting options.
ostream << format(i,6,CentreAlign,Hex);

Functionality

            Always check the formatter's interface to see what setters are
            available to the type you wish to format. Although there are common
            formatting parameters, they are few and these will usually vary from type
            to type.

Performance

            Some results from tests on a 64 bit gentoo installed on a dual core II computer
            while formatting both integer and float types indicate that when used in conjunction
            with TextStream, the formatters are 7-30x faster than their printf and
            iostream equivalents (which perform roughly as well as each other).
            Run the test program for evaluation on your machine.

Health Hazards

            There are some awkward aspects of streaming that make it difficult for the formatters to
            function perfectly. Without going into the details, there are various issues with
            the unspecifiedness of function arguments that mean its impossible to format several
            objects on the same line differently, and expect the result to come back in the
            correct order. I haven't currently got a solution for this, so there are two
            options:
            - 1) Leave the formatters as they are and ensure that only one
            formatter is used on each line (abort/throw if this occurs), or
            - 2) Push the formatters back into TextStream.

            The second option is no good - it just turns TextStream into a heavyweight iostream.
            A priority for us is fast logging, so we must keep TextStream lightweight and since
            1) is merely a coding style issue, that's easy to handle so long as we are aware of
            it.

Permitted Usage

ostream << "[" << format(q.x());
ostream << ", " << format(q.y());
ostream << ", " << format(q.z()) << "]";

Not permitted Usage

ostream << "[" << format(q.x()) << ", " << format(q.y()) ostream << ", " << format(q.z()) << "]";

In debug mode, formatters use an exception throwing assert to check that multiple formatters aren't used in the one line when streaming.

Types

            Formatters cover all the basic fundamental types (char, float, double, int...). They
            also cover a few special types, including arrays - refer to the documentation for ecl_containers
            for more information.

Writing Your Own Formatters

            Formatters must implement
            - Formatting setters
            - Input value operator
            - Temporary formatting operators
            - Streaming friend function
class MatrixFormatter {
public:
MatrixFormatter& precision(int p); // Setter
MatrixFormatter& operator()(Matrix M); // Input Operator
MatrixFormatter& operator(int p, int w ... ); // Combination setter
MatrixFormatter& operator(Matrix M, int p, int w ...); //Temporary formatting operator
template <typename OutputStream, typename N> friend OutputStream& operator << (OutputStream& ostream, MatrixFormatter& formatter);
}

Note that the setters and operators must return the formatter so that the friend function can implement the formatting.

For the Format<Type> class to automagically find this formatter, you can implement one of two methods. If you have access to the class's internals, simply typedef it as "Formatter" inside the class, otherwise simply specialise the Format<> class for your type and inherit the formatter.

// Method one, if you have access to the classes internals
class Matrix {
public:
typedef MatrixFormatter Formatter;
};
// Method two
template <>
class Format<Matrix> : public MatrixFormatter {};

Current List of Fundamental Converters

            Each standard formatter is a template specialisation of the form Format<inputType> where the available input types are:

            - integral types (char, short, int, long, long long and their unsigned equivalents)
            - float types (float, double)
            - string
            - fixed size arrays/stencils

            Note, as with any string based object, avoid it if you need speed with your streaming.

Unit Tests

    - src/examples/formatters.cpp : not a google unit test, but does coverage.

ChangeLog

- <b>Sep 10</b> : Moved container arrays to the ecl_containers class.
- <b>Mar 10</b> : Char stencils can now use the same formatter as their underlying array.
- <b>May 09</b> : Added width formatting capabilities to float containers.
- <b>May 09</b> : Added formatters for fixed size char, float and double arrays.
- <b>May 09</b> : Fixed speed issues by converting to an underlying snprintf implementation (temp. hack).
- <b>May 09</b> : Added formatters for fundamental number types and strings.


ecl_formatters
Author(s): Daniel Stonier
autogenerated on Thu Jun 6 2019 21:58:38