Try/Catch unordered map exception properly

Question

i have got this:

// static enum of supported HttpRequest to match requestToString
static const enum HttpRequest {
    GET, 
    POST,
    PUT,
    DELETE,
    OPTIONS,
    HEAD,
    TRACE
};

// typedef for the HttpRequests Map
typedef boost::unordered_map<enum HttpRequest, const char*> HttpRequests;

// define the HttpRequest Map to get static list of supported requests
static const HttpRequests requestToString = map_list_of
    (GET,    "GET")
    (POST,   "POST")
    (PUT,    "PUT")
    (DELETE, "DELETE")
    (OPTIONS,"OPTIONS")
    (HEAD,   "HEAD")
    (TRACE,  "TRACE");

now if i call

requestToString.at(GET);

it´s ok, but if i call an key which is not present like

requestToString.at(THIS_IS_NO_KNOWN_KEY);

it gives a runtime exception and the whole process aborts..

whats the best way to prevent this? is there a pragma or what ever or should i "java-like" surround it with a try/catch block or what?

kindly alex

Answer 1

Use at if you want an exception if it's not found, and handle the exception somewhere if you don't want it to terminate the process; use find if you want to handle it locally:

auto found = requestToString.find(key);
if (found != requestToString.end()) {
    // Found it
    do_something_with(found->second);
} else {
    // Not there
    complain("Key was not found");
}

Answer 2

You can use unordered_map::find to search for a key that may or may not be in the map.

find returns an iterator, which is either == end () if the key is not found, or "points to" a std::pair if the key was found.

Uncompiled code:

unordered_map < int, string > foo;
unordered_map::iterator iter = foo.find ( 3 );
if ( iter == foo.end ())
     ; // the key was not found in the map
else
     ; // iter->second holds the string from the map.