integers, chars and floating points in structs

Question

So, I'm having some issues with my c++ code. I have the following code, but so far I can't get most of the data stored into the structured data type.

    //structured data declaration
    struct item
    {
        int itemCode;
        char description[20];
        float price;
    };

And then the get code looks like this.

cout << setprecision(2) << fixed << showpoint;

ofstream salesFile ("Sales.txt");
ifstream stockFile ("Stock.txt");
for (counter = 0; counter < 9; counter++)
{
    stockFile >> instock[counter].itemCode;
    stockFile.getline (instock[counter].description, 20);
    stockFile >> instock[counter].price;
}

The output should have looked like:

1234 "description here" 999.99 Quantity X

And this was the output:

1234 0.00 Quantity 5

If the description is on the line after the item code, you need to read past the newline before calling `getline()`. Otherwise it will just read the rest of the line after the item code. — Barmar, Apr 13 '17 at 22:46
http://stackoverflow.com/questions/5739937/using-getlinecin-s-after-cin?rq=1 — stark, Apr 13 '17 at 23:15
Reduce your defects and use `std::string` for handling text. — Thomas Matthews, Apr 13 '17 at 23:17

score 1 · Answer 1 · answered Apr 13 '17 at 23:14

If you have a file format that is of the form (for one entry)

1234
description here
999.99

(across multiple lines) then the explanation is simple

Th reading code in your loop, which does

stockFile >> instock[counter].itemCode;
stockFile.getline (instock[counter].description, 20);
stockFile >> instock[counter].price;

will work in this sequence

The value of instock[counter].itemCode will receive the value 1234. However (and this is important to understand) the newline after the 1234 will still be waiting in the stream to be read.
The call of getline() will encounter the newline, and return immediately. instock[counter].description will contain the string "".
The expression stockFile >> instock[counter].price will encounter the d in description. This cannot be interpreted as an integral value, so instock[counter].price will be unchanged.

Assuming some preceding code (which you haven't shown) sets instock[counter].price to 999.99 the above sequence of events will explain your output.

The real problem is that you are mixing styles of input on the one stream. In this case, mixing usage of streaming operators >> with use of line-oriented input (getline()). As per my description of the sequence above, different styles of input interact in different ways, because (as in this case) they behave differently when encountering a newline.

Some people will just tell you to skip over the newline after reading instock[counter].itemCode. That advice is flawed, since it doesn't cope well with changes (e.g. what happens if the file format changes to include an additional field on another line?, what happens if the file isn't "quite" in the expected format for some reason?).

The more general solution is to avoid mixing styles of input on the one stream. A common way would be to use getline() to read all data from the stream (i.e. not use >> to interact directly with stockFile). Then interpret/parse each string to find the information needed.

Incidentally, rather than using arrays of char to hold a string, try using the standard std::string (from standard header <string>). This has the advantage that std::string can adjust its length as needed. std::getline() also has an overload that can happily read to an std::string. Once data is read from your stream as an std::string, it can be interpreted as needed.

There are many ways of interpreting a string (e.g. to extract integral values from it). I'll leave finding an approach for that as an exercise - you will learn more by doing it yourself.

I do appreciate the help, but unfortunately the prompt for this assignment explicitly forbid the use of string objects. However, using the getline() operator was my initial thought as well, but I was unsure whether or not it could be used for integers and floating point variables. — Trace Langfels, Apr 14 '17 at 06:32
Then use `getline()` to read a line to an array of `char`, and parse that. You may have to check for and deal with the potential of lines in the file being longer than your array though. — Peter, Apr 14 '17 at 06:41

integers, chars and floating points in structs

1 Answers1