In C++, exceptions can be thrown and caught in different parts of a program, and the order in which they are caught can affect the behavior of the program. Exception propagation refers to the process of passing an exception from the point where it was thrown to the point where it is caught, while catching order refers to the sequence in which the catch blocks are evaluated to handle the thrown exception.

When an exception is thrown, the program starts searching for a catch block that can handle the exception. It searches for the catch block in the current function, and if it is not found, it moves up the call stack to the caller function. This process continues until either a matching catch block is found, or the exception reaches the top of the call stack and is not caught, resulting in program termination.

The order in which catch blocks are evaluated is important because the first catch block that matches the exception type is the one that handles the exception. If the catch blocks are not ordered correctly, a more specific catch block may not be evaluated before a more general catch block that can also handle the exception.

For example, consider the following code:

try {
    // code that may throw an exception
}
catch (std::exception& e) {
    // handle exceptions of type std::exception or its subclasses
}
catch (...) {
    // handle any other exceptions
}

In this example, the first catch block can handle any exception that is a subclass of std::exception, while the second catch block can handle any other exception. If the catch blocks were reversed, the more specific catch block would never be evaluated, as the more general catch block would handle all exceptions.

In summary, the order in which catch blocks are evaluated can affect the behavior of a program, and it is important to order them correctly to ensure that exceptions are handled properly.