C++ Flow Control throw
Example
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When
throwoccurs in an expression with an operand, its effect is to throw an exception, which is a copy of the operand.void print_asterisks(int count) { if (count < 0) { throw std::invalid_argument("count cannot be negative!"); } while (count--) { putchar('*'); } } -
When
throwoccurs in an expression without an operand, its effect is to rethrow the current exception. If there is no current exception,std::terminateis called.try { // something risky } catch (const std::bad_alloc&) { std::cerr << "out of memory" << std::endl; } catch (...) { std::cerr << "unexpected exception" << std::endl; // hope the caller knows how to handle this exception throw; } -
When
throwoccurs in a function declarator, it introduces a dynamic exception specification, which lists the types of exceptions that the function is allowed to propagate.// this function might propagate a std::runtime_error, // but not, say, a std::logic_error void risky() throw(std::runtime_error); // this function can't propagate any exceptions void safe() throw();Dynamic exception specifications are deprecated as of C++11.
Note that the first two uses of throw listed above constitute expressions rather than statements. (The type of a throw expression is void.) This makes it possible to nest them within expressions, like so:
unsigned int predecessor(unsigned int x) {
return (x > 0) ? (x - 1) : (throw std::invalid_argument("0 has no predecessor"));
}
