report.hpp

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/**
 * @file
 * @ingroup daq_error
 * @copyright ESO - European Southern Observatory
 */
#ifndef DAQ_ERROR_REPORT_HPP
#define DAQ_ERROR_REPORT_HPP
 
#include <exception>
#include <iosfwd>
 
namespace daq::error {
 
void ReportNestedExceptions(std::ostream& os) noexcept;
void ReportNestedExceptions(std::ostream& os, std::exception const& e) noexcept;
 
 
/**
 * Report nested exception(s) in @a exception messages to @a os.
 *
 * If @a ptr does not hold an exception this function has no effect.
 *
 * @param os output stream to report to.
 * @param ptr exception (possibly nested) to report.
 */
void ReportNestedExceptions(std::ostream& os, std::exception_ptr ptr);
 
/**
 * Report without nesting.
 *
 * @param os output stream to report to.
 * @param ptr exception (possibly nested) to report.
 */
void FormatException(std::ostream& os, std::exception_ptr ptr);
 
/**
 * Return formatted exception.
 *
 * @param ptr exception (possibly nested) to report.
 * @return formatted string (mainly std::exception::what())
 */
std::string FormatException(std::exception_ptr ptr);
 
 
/**
 * Adapter object intended to be used in contexts without direct access to the output-stream object.
 *
 *     try {
 *       MaybeThrows();
 *     } catch (std::exception const& e) {
 *       LOG4CPLUS_ERROR(logger, "MaybeThrow failed with:\n" << NestedExceptionReporter(e));
 *     }
 */
class NestedExceptionReporter {
public:
    /**
     * Construct from exception derived from std::exception.
     */
    explicit NestedExceptionReporter(std::exception const& exception) noexcept
        : m_ptr(), m_exception(&exception){};
    /**
     * Construct from exception_ptr.
     */
    explicit NestedExceptionReporter(std::exception_ptr ptr) noexcept
        : m_ptr(std::move(ptr)), m_exception(nullptr){};
 
    /**
     * Convenience function for constructing a std::string from the exception.
     *
     * @return Formatted string
     */
    std::string Str() const;
 
    /**
     * Formats exception from @a reporter using ReportNestedExceptions.
     *
     * @param os output stream to output to.
     * @param reporter Reporter adapter to format.
     * @returns os
     */
    friend std::ostream& operator<<(std::ostream& os, NestedExceptionReporter const& reporter) {
        if (reporter.m_ptr) {
            ReportNestedExceptions(os, reporter.m_ptr);
        } else if (reporter.m_exception) {
            ReportNestedExceptions(os, *reporter.m_exception);
        }
        return os;
    }
 
private:
    // A variant or union would occupy same space so this was preferred over
    // including <variant>
    std::exception_ptr m_ptr;
    std::exception const* m_exception;
};
 
 
 
}  // namespace daq::error
#endif  // #ifndef DAQ_ERROR_REPORT_HPP