ecl_errors Documentation

ecl_errors

This library provides lean and mean error mechanisms. It includes c style error functions as well as a few useful macros. For higher level mechanisms, refer to ecl_exceptions.

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

packageSummary

The usual C++ means is to use exceptions, however in embedded systems, exceptions are often unavailable or are too resource-heavy. This library provides a simpler alternative, combining error flags, macros and an error handler class to provide convenient disposal of errors across multiple platforms.

It also provides simple runtime and compile time asserts and aborts.

CompilingLinking

Include the following at the top of any translation unit:

        #include <ecl/errors.hpp>

        // The error interfaces
        using ecl_compile_time_assert;
        using ecl_run_time_assert;
        using ecl_run_time_abort;

        // Error type enumerations
        using ecl::NoError;
        using ecl::ConfigurationError;
        using ecl::UnknownError;
        //...
        
        // Error Handler
        using ecl::Error;

You will also need to link to -lecl_errors.

Usage

LOC

The macro, LOC, is a means of picking up the current file and line number of the point at which it is processed. Use with the various error functions and functors defined in ecl::errors;

Error Handling

A set of flags is provided through the enumeration ErrorFlag. These, when coupled with the errorhandler class and LOC macro provide a convenient means of quickly identifying errors produced by the ecl libraries regardless of the platform that is used.

                ecl::Error void f(const int &i) const {
                    if ( i == 3 ) {
                        return ecl::Error(ecl::NoError);
                    } else {
                        return ecl::Error(ecl::OutOfRangeError);
                    }
                int main() {
                    ecl::Error error = f(5);
                    if ( error.flag() != NoError() ) {
                        error.print(loc);  
                    }
                    // output is ~ 'my_main.cpp : 31 - Out of range error.'
                    return 0;
                }

The Error class can be extended to customise the error messages - refer to the ecl_time_lite package and the ecl::TimeError class for an example.

Assert and Abort Functions

These functions, because they are coupled with fallback macros are the only functions in the ecl not namespaced inside the ecl namespace. Rather they are prefixed with ecl_.

The ecl_run_time_assert macro/function is a tool for conditional testing. It is governed by the presence of the NDEBUG macro. If NDEBUG is absent (either in your code or c-flagged by the compiler (-DNDEBUG) then run_time_assert will equate to a macro that defers to a null function pointer. This is the fastest means of bypassing debugged code.

If NODEBUG is present, then ecl_run_time_assert will act as a conditional test via an function. If the test fails, it will output some data (that you have passed to the function) before finally aborting.

                int i = 3;
                int j = 2;
                ecl_run_time_assert(i < j, LOC, "Illegal context, need i < j");

The abort macro/function works similarly except that it does no conditional test and it is not negated by the presence of NDEBUG.

Compile Time Equivalents

There is also a macro which works like the compile time equivalent of ecl_run_time_assert(). This macro is useful for checking template parameters mostly. When passed a logical condition which fails, an eye-catching COMPILE_TIME_FAILURE is reported in the compile log.

                ecl_compile_time_assert( 1 > 3 )

Corresponding failure is reported in a format similar to the example output shown below:

                test.cpp:47: error: invalid application of ‘sizeof’ to incomplete type ‘COMPILE_TIME_FAILURE<false>’ 

Other Notes

A short ramble on how the ecl handles debugging can be found in this guide.

unitTests

Not gtests, but a useful enough coverage style test.

• src/examples/errors.cpp

ChangeLog

• ChangeLog