ecl_streams Documentation

ecl_streams

These are lightweight text streaming classes that connect to standardised ecl type devices.

• Homepage: http://wiki.ros.org/ecl_streams

Embedded Control Library

    Streams provide a standardised c++ interface for connecting to
    ecl input-output devices.

    - speed : control cannot afford serious slowdowns for convenience.
    - extensible : must be able to create new devices easily.
    - streams : all devices should connect in a standardised way to streams.

Comparison

    Finding a library with a standard/extensible interface that
    works across devices and implements streaming operators is
    like trying to find the pot at the bottom of the rainbow.

Compiling & Linking

    Include the following at the top of any translation unit which
    requires this library:

#include <ecl/streams.hpp>

// Templatised all purpose stream
using ecl::TextStream;

// Convenience stream handles
using ecl::IConsoleStream;
using ecl::OConsoleStream;
using ecl::EConsoleStream;
using ecl::OFileStream;
using ecl::SerialStream;
using ecl::SharedFileStream;
using ecl::SocketClientStream;
using ecl::SocketServerStream;
using ecl::StringStream;

// Special customised streams
using ecl::LogStream;

// Stream manipulators
using ecl::endl;
using ecl::clrscr;

You will also need to link to -lecl_streams.

Usage

Open/Close

            Each stream-device pair can be instantiated via the generic TextStream object and the
            underlying device opened via the device() member method. For example,

TextStream<OFile> stream;
stream.device().open("dude.txt",New);

The console device is a special case - it is automatically opened.

Convenience Classes

The preferred method of instantiation is via the constructor in the convenience classes. The convenience classes are specialised interfaces that inherit from the appropriate Textstream type (dependant on the template parameter). Examples, SerialStream, OFileStream. Rather than calling stream.device().open(...) directly, you can use their constructors to instantiate the stream. They are also more convenient than typing out template parameters continuously.

OFileStream stream("dude.txt",New);

Output Streams

            Output streams function similarly to the familiar cout stream. The primary advantage being that
            they can easily be attached to any standard ecl io device. They can also be used with the
            ecl_formatter classes.

OFileStream ostream;
Format<double> format; format.width(5); format.precision(2);
double d = 1.0/3.0;
ostream << format(d);  // This will send 0.33 to the stream.
ostream.flush();

Input Streams

            There are three ways to utilise an input stream:

            - reading element by element (separated by whitespace or newlines).
            - reading raw characters (you must call enableRawCharReads()).
            - reading line by line (not yet enabled).

            The first method is similar to the familiar cin, it will take a string and convert it to the requested type.

IConsoleStream istream;
double d;
istream >> d;

The second method is sometimes useful when communicated with raw character devices (e.g. a serial line). In this situation, you must simply make use of the char input operator.

SerialStream serial_stream;
char c;
if ( serial_stream.device().remaining() ) {
        serial_stream >> c;
}

The third method has not yet been implemented.

Logging Streams

            @ref ecl::LogStream "LogStreams" are a convenient, fast means to
            logging from multiple threads with multiple customisable modes. They can
            also optionally automatically insert header and timestamp information.

            Multiple modes are most conveniently utilsed via customised enums. For example:

enum LogModes {
   Warning,
   Error,
   Debug,
};

Note that this is an advantage over alot of other loggers in that it gives you the freedom to define your own error logging levels. Each mode can then be associated inside the log stream with its own customised header.

LogStream log_stream("test.log")
log_stream.enableMode(Warning,"WARNING");
log_stream.enableMode(Error,"ERROR");
log_stream.enableMode(Debug,"DEBUG");

This process can be repeated from multiple threads each with its own instance of the log stream attached to the single file. Using the log stream is then done via the macros LOG and FLUSH

LOG(log_stream, Warning) << "This is a log message from main().\n";
FLUSH(log_stream)

By default this will automatically add header and timestamp information. You can manually disable these if you prefer.

Error Checking

    Output streams can generate errors that are not so easily checked compared with handling devices directly.
    To check for failure, ecl streams use a mechanism similar to that of the standard cout stream.

ostream << 32.1;
if ( ostream.fail() ) {
        std::cout << ostream.errorStatus().what() << std::endl;
}

Manipulators

    ECL manipulators are defined to enable some similar functionality to c++'s cout manipulators.
    However they extend the concept to use class instantiations rather than functions. This
    provides one important advantage over the former, these manipulators can retain state. Given
    that they're also easy to customise, this opens up many possibilities.

    The default manipulators defined in the ecl export a few global instantiations,
    namely

    - ecl::endl
    - ecl::clrscr

    Using manipulators follows the same pattern as for standard c++ style cout manipulators.

int main() {
        ecl::OConsoleStream ostream;
        ostream << ecl::clrscr;
        ostream << "Dude" << ecl::endl;
        return;
}

Creating your own Manipulators:

Any manipulator that you wish to define must inherit from this parent class in the following manner:

include <ecl/streams/manipulators.hpp>

class MyManipulator : public ecl::Manipulator<MyManipulator> {
        template <typename OutputStream>
        void action (OutputStream& ostream) {
                // ...
        }
};

Benchmarking

    The following results are for streaming/flushing a large number of strings/floats
    to various devices/streams. It was performed on a 32 bit single core intel processor
    running linux (kernel 2.6.31) (exact values aren't important, rather the relative
    differences).

Writing Char Strings:
   OFile write       : 58806 ns
   SharedFile write  : 47562 ns
   OFile stream      : 61739 ns
   LogStream         : 73753 ns
   C++ ofstream      : 83321 ns
Streaming Floats:
   OFileStream       : 693593 ns
   Log stream        : 711753 ns
   C++ ofstream      : 862120 ns

Unit Tests

    - src/test/file_streams.cpp
    - src/test/string_streams.cpp

Demos

    - src/examples/console_streams.cpp
    - src/examples/log_streams.cpp

Utilities

    - ecl_core_apps/src/benchmarks/streams.cpp
    - ecl_core_apps/src/benchmarks/files.cpp

ChangeLog

    - @ref changelog "ChangeLog"