I have the following loop. It should read numbers until EndOfFile
, or the user input -999
int arr[100];
int index;
for (index = 0; index < 100; index++)
{
cin >> arr[index];
if (!cin)
{
cin.clear();
index--;
continue;
}
if (arr[index] == -999)
{
break;
}
}
When the user input an invalid thing开发者_运维知识库, such as some char
s, this loop is being repeated for ever without clear
ing the error state or stopping.
After calling clear
, you must also somehow remove the invalid input from the stream. Here is one way:
cin >> arr[index];
if (!cin)
{
cin.clear();
std::string ignoreLine; //read the invalid input into it
std::getline(cin, ignoreLine); //read the line till next space
index--;
continue;
}
It's because when cin
fails to read the invalid input, it remains there in the stream. It has to be removed, by some means. I just read and ignore it.
You can also use ignore
as:
cin.clear();
cin.ignore(std::numeric_limits<streamsize>::max(),' ');
which is better in my opinion provided inputs are space separated (and if you don't want to inspect the invalid input). The online doc says:
istream::ignore
istream& ignore( streamsize n = 1, int delim = EOF );
Extract and discard characters
Extracts characters from the input sequence and discards them.
The extraction ends when n characters have been extracted and discarded or when the character delim is found, whichever comes first. In the latter case, the delim character itself is also extracted.
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