Flow-control structures: Difference between revisions
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Note that "goto" may also be used in conjunction with other forms of branching.
==== Exceptions ====
'''Compiler:''' [[GCC]] 4.0.2
Exceptions are a way to give control back to a direct or indirect caller in case of an error.
#include <iostream>
#include <ostream>
void foo()
{
std::cout << "Going to throw an exception.\n";
throw 7; // almost any object can be thrown, including ints
std::throw << "This output will never execute.\n";
}
void bar()
{
std::cout << "Going to call foo().\n";
foo();
std::cout << "This will be skipped by the exception coming from foo.\n";
}
void baz()
{
try // everything thrown from inside the following code block
{ // will be covered by the following catch clauses
std::cout << "Going to call bar().\n";
bar();
std::cout << "This will be skipped by the exception coming from foo.\n";
}
catch(...) // a simple catch-all, but doesn't give access to the thrown exception
{
std::cout << "An exception occured. I'll just throw it on.\n";
throw; // without an argument, the caught exception is re-thrown
}
std::cout << "This will not be executed due to the re-throw in the catch block\n";
}
void foobar()
{
try
{
baz();
}
catch(char const* s)
{
std::cout << "If foo had thrown a char const*, this code would be executed.\n";
std::cout << "In that case, the thrown char const* would read " << s << ".\n";
}
catch(int i)
{
std::cout << "Caught an int, with value " << i << " (should be 7).\n";
std::cout << "Not rethrowing the int.\n";
}
catch(...)
{
std::cout << "This catch-all doesn't get invoked because the catch(int) above\n"
<< "already took care of the exception (even if it had rethrown the\n"
<< "exception, this catch-all would not be invoked, because it's\n"
<< "only invoked for exceptions coming from the try block.\n";
}
std::cout << "This will be executed, since the exception was handled above, and not rethrown.\n";
}
int main()
{
try
{
foobar();
}
catch(...)
{
std::cout << "The main function never sees the exception, because it's completely handled\n"
<< "inside foobar(). Thus this catch-all block never gets invoked.\n";
}
}
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Revision as of 22:39, 26 January 2007
In this task, we document common flow-control structures. One common example of a flow-control structure is the goto
construct. Note that Conditional Structures and Loop Structures have their own articles.
C++
goto
Compiler: GCC 3.3.4
#include <iostream> int main() { LOOP: std::cout << "Hello, World!\n"; goto LOOP; }
Note that "goto" may also be used in conjunction with other forms of branching.
Exceptions
Compiler: GCC 4.0.2 Exceptions are a way to give control back to a direct or indirect caller in case of an error.
#include <iostream> #include <ostream> void foo() { std::cout << "Going to throw an exception.\n"; throw 7; // almost any object can be thrown, including ints std::throw << "This output will never execute.\n"; } void bar() { std::cout << "Going to call foo().\n"; foo(); std::cout << "This will be skipped by the exception coming from foo.\n"; } void baz() { try // everything thrown from inside the following code block { // will be covered by the following catch clauses std::cout << "Going to call bar().\n"; bar(); std::cout << "This will be skipped by the exception coming from foo.\n"; } catch(...) // a simple catch-all, but doesn't give access to the thrown exception { std::cout << "An exception occured. I'll just throw it on.\n"; throw; // without an argument, the caught exception is re-thrown } std::cout << "This will not be executed due to the re-throw in the catch block\n"; } void foobar() { try { baz(); } catch(char const* s) { std::cout << "If foo had thrown a char const*, this code would be executed.\n"; std::cout << "In that case, the thrown char const* would read " << s << ".\n"; } catch(int i) { std::cout << "Caught an int, with value " << i << " (should be 7).\n"; std::cout << "Not rethrowing the int.\n"; } catch(...) { std::cout << "This catch-all doesn't get invoked because the catch(int) above\n" << "already took care of the exception (even if it had rethrown the\n" << "exception, this catch-all would not be invoked, because it's\n" << "only invoked for exceptions coming from the try block.\n"; } std::cout << "This will be executed, since the exception was handled above, and not rethrown.\n"; } int main() { try { foobar(); } catch(...) { std::cout << "The main function never sees the exception, because it's completely handled\n" << "inside foobar(). Thus this catch-all block never gets invoked.\n"; } }