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Hello,
Im trying to understand chapter 4 of Accelerated C++.
But one thing I can't understand.
We try to read the homework grades from input stream into a vector <double>
istream& read_hw (istream& in, vector <double>& hw)
If I understand it right read_hw is another name for istream
And in is another name for istream.
But what's istream here doing. I tought that cin reads data in.
Can someone shine a light on this ?
Roelof
"read_hw" looks like a function prototype to me, it returns a reference to an istream, probably the same stream it takes in, because it's going to be used to read data from that stream. Lemme see if I can write you an example of that, but I have to finish something else first...
Yes, cin is an istream.
Yeah, from what I understand cin is an istream, and when you call this function you will (in this instance) call as such: read_hw(cin, homework), with homework being the vector name.Quote:
Originally Posted by roelof
It's a function prototype. It defines a new function that takes two arguments:
- An istream (input stream).
- A vector of doubles.
It will then read from the input stream and store the data in the double (hw).
When you call this function, you pass either cin or some opened file as the argument for in.
Oke,
And hw_read is then the name of the new function ?
Does this the same as :
cin >> name
homework.push_back (name) ;
or do I understand your wrong ?
Roelof
Roelof
You still need to write the code within the function for it to do something. Within that chapter, i'm sure it shows an example of what the function body should look like for the read_hw function.Quote:
Originally Posted by roelof
Yes.Quote:
Originally Posted by roelof
It will do whatever you code it to do.
Oke,
When I read further I saw the whole function.
But why first prototype a function and right after that write the code in it ?
Roelof
I believe the book was just showing you how the function would look like (ie what parameters it takes and what it returns).
That will actually become fairly standard once you reach classes. Mainly for readability, with classes (particularly for functions more than a few lines long), you will declare the functions within the class and then define them outside of the class.Quote:
Originally Posted by roelof
Oke,
Then I will now read the part of how the data will change from the earlier chapter.
Thanks everybody for the help and explanation.
Roelof
Hello
I read now the whole chapter and saw that the prototype is used in the header file and the function itself in the main file.
Now trying to make the exercises.
Roelof