Error Reporting

Exceptions and assertions provided by VIGRA

#include <vigra/error.hxx>

VIGRA defines the following exception classes:

namespace vigra {
    class ContractViolation : public std::exception;
    class PreconditionViolation : public ContractViolation;
    class PostconditionViolation : public ContractViolation;
    class InvariantViolation : public ContractViolation;
}

The following associated macros throw the corresponding exception if their PREDICATE evaluates to 'false':

vigra_precondition(PREDICATE, MESSAGE);
vigra_postcondition(PREDICATE, MESSAGE);
vigra_invariant(PREDICATE, MESSAGE);

The MESSAGE is passed to the exception and can be retrieved via the overloaded member function 'exception.what()'. If the compiler flag 'NDEBUG' is not defined, the file name and line number of the error are automatically included in the message. The macro

vigra_assert(PREDICATE, MESSAGE);

is identical to vigra_precondition() except that it is completely removed when 'NDEBUG' is defined. This is useful for test that are only needed during debugging, such as array index bound checking. The following macro

vigra_fail(MESSAGE);

unconditionally throws a 'std::runtime_error' constructed from the message (along with file name and line number, if NDEBUG is not set).

Usage:

Include-File: <vigra/error.hxx>

Namespace: vigra (except for the macros, of course)

int main(int argc, char ** argv)
{
    try
    {
        const char* input_file_name = argv[1];

        // read input image
        vigra::ImageImportInfo info(input_file_name);

        // fail if input image is not grayscale
        vigra_precondition(info.isGrayscale(), "Input image must be grayscale");

        ...// process image
    }
    catch (std::exception & e)
    {
        std::cerr << e.what() << std::endl; // print message
        return 1;
    }

    return 0;
}