The issue of std::exception not being caught in C++ can arise due to several reasons:

1. Incorrect Exception Type – std::exception does not have a constructor that takes a string argument. Instead, use std::runtime_error or std::logic_error to pass an error message.

2. Heap Allocation of Exception – If an exception is thrown using throw new some_exception and caught with catch (some_exception &exc), it won’t be caught because new returns a pointer, and exception handling expects an object reference.

3. Buffering Issues in Output – If the exception is caught but not printing, ensure std::cerr is used instead of std::cout, or add \n at the end of the error message for immediate output.

4. Compiler/Debugger Settings – Some compilers require enabling C++ exceptions explicitly. Also, breakpoints set before the throw statement can sometimes mislead debugging.