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Write a program to demonstrate the catching of all exceptions what happens when a raised exception is not caught by catch block in the absence of a catch all exception block?
Wiki User
∙ 9y ago
If an exception is not caught then your program has undefined behaviour. Ultimately the program crashes, but since you haven't handled the exception you've no way of knowing what damage has been done. Files could be wiped or currupted, planes could fall from the sky... anything is possible with undefined behavour.
The best way to deal with unknown exceptions is to first catch them with a catch-all. However, you cannot actually handle the exception unless you know what type of exception you are actually dealing with. Thus the normal course of action is to assume the worst, perform any and all necessary cleanup, log the exception as an unknown exception and rethrow. As the exception percolates back down the call stack, all other exception handlers should do the same: cleanup, log and rethrow. If you're lucky, another handler might recognise the exception and be able to provide more detailed information on the type of exception. Ultimately you must never allow a program to continue executing if you cannot handle an exception.
C++11 offers a more elegant solution using a nested try catch within a catch-all. However, it makes more sense to place the nested try catch in a global function (e.g., handle_eptr()) which can specifically deal with all catch-all exceptions. Like so...
#include <iostream>
#include <string>
#include <exception>
#include <stdexcept>
void handle_eptr(std::exception_ptr eptr)
{
try
{
if (eptr) std::rethrow_exception (eptr);
}
catch (const std::exception& e)
{
std::cerr << "Exception: "" << e.what() << ""\n";
}
}
int main()
{
try
{
std::string().at(1); // throws "invalid string position"
}
catch(...) // catch-all
{
// perform any necessary cleanup here before calling the global handler
handle_eptr (std::current_exception());
}
}
Output:
Exception: "invalid string position"
Note that handle_eptr() receives a std::exception_ptr. By itself this is useless, but std::rethrow_exception() converts the eptr to a standard exception which can then be thrown, caught and logged. You must still perform any necessary cleanup and allow the program to terminate gracefully, but at least you now know what type of exception you are dealing with and can provide a specific handler to handle it.
Note that handle_eptr() should be fleshed out to accept all necessary debug information such as the filename and the line number from the catch_all that called it. The example merely demonstrates how to pass the eptr and convert it into an actual exception.
Wiki User
∙ 9y ago
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