Code sketch of a mechanism for attaching additional context to exceptions

econtext.cpp

#include "econtext.h"

__thread std::vector<ExceptionContextItem> currentContext;

typedef void (*cxa_throw_type)(void *, void *, void (*) (void *));
static cxa_throw_type orig_cxa_throw = 0;
 
static void load_orig_throw_code()
{
    orig_cxa_throw = (cxa_throw_type) dlsym(RTLD_NEXT, "__cxa_throw");
}
 
extern "C"
void __cxa_throw (void *thrown_exception, void *pvtinfo, void (*dest)(void *)) {
    if (!orig_cxa_throw)
        load_orig_throw_code();

    currentContext.clear();
    orig_cxa_throw(thrown_exception, pvtinfo, dest);
}

econtext.hpp

#ifndef _ECONTEXT_HPP
#define _ECONTEXT_HPP

#define EXCEPTION_CONTEXT("row", x) \
    scoped_exception_context<typeof(x)> ("row", &x);

template<typename T>
struct scoped_exception_context
{
public:
    scoped_exception_context(const char* name, T* val) {
    }
    ~scoped_exception_context() {
        if (std::uncaught_exception()) {
            currentContext.push_back(name, boost::lexical_cast<std::string>(val));
        }
    }
private:
    const char* name;
    T* val;
};

struct ExceptionContextItem {
    const char * name;
    std::string value;
};

__thread std::vector<ExceptionContextItem> currentContext;

#endif // _ECONTEXT_HPP

example.cpp

try {
    size_t row = 0, col = 0;
    
    EXCEPTION_CONTEXT("row", row);
    EXCEPTION_CONTEXT("col", col);
    
    for (row = 0; row < row_count; row++)
        for (col = 0; col < col_count; col++) {
            EXCEPTION_CONTEXT("contents", data[row][col])
            if (!validate(data[row][col]))
                throw validation_failed();
        }
}
catch (validation_failed&)
{
    dialog("Loading simulation failed because cell " + context["row"] + ", " + context["col"]
           + " of " + context["filename"] + " contains '" + context["contents"] + "' when it"
           "should contain a number");
}