Input validation

[tensity]

I was wondering how one might go about the following:

I am reading in data from a file using getline(inputFile, tempString). Some of this information has to stay in string format, and other information must be converted to floats, ints, etc.

I anticipate there being a problem if there is an error in the file and one of the pieces of data that should be read into an int is read into a string. For instance, if there were a file as follows:

100             should be read and converted to int
100.23          should be read and converted to a float
100 spring ln   should be read and stay a string
Michael         should be read and stay a string
101             should be read and converted to int
100.50          should be read and converted to float
101 spring ln   should be read and stay a string
100.58          should be read and stay a string --- WOULD CREATE A NOT SO OBVIOUS ERROR
102 spring ln   should be read and converted to int --- OBVIOUS ERROR
Steven          should be read and converted to float --- OBVIOUS ERROR

the code that is reading the file is a loop until EOF. Is there any way to check for the not so obvious error?

[deceptikon]

Rather than treat each line as separate and independent, collect them in a record where you can validate each field as it relates to the others. So for line 8 you'd be looking for a name, correct? Digits are a clear case of error when looking for a name, so that would fail the validation check and subsequently cause you to stop reading the file because it's clearly malformed.

[NathanOliver]

what does the actual contents of the file look like?

[tensity]

first name
last name
address
id number
credits completed
quality points

[tensity]

I have started working through this. Here is one issue that I have encountered:
when converting an int or float from a string, if it converts a "0" to a 0, the program sees it as an error. Here is the code.

if(!(id = atoi(qual.c_str()))) {
    cout << "***Invalid quality points read from file. Quiting.***" << endl;
    system("pause");
    exit (EXIT_FAILURE);
}

In this case, 0 quality points is an acceptable value. Should I create nested if's to see first if the number is a 0?

[Lucaci Andrew]

You could use the stringstream class.

[deceptikon]

when converting an int or float from a string, if it converts a "0" to a 0, the program sees it as an error.

That's one of the primary reasons why you shouldn't use atoi(). The other reason is that if the string doesn't represent a number, you invoke undefined behavior. I posted an example not to long ago on how to properly use strtol() as a replacement for atoi(): Click Here.

However, since this is C++, I'd favor a stringstream (which includes validation that doesn't affect the result), or C++11's stoi() (which will throw an exception for errors rather than overload the return value).