How do i set a function to a constant variable?

Question

It's been a while since I have worked in C++, I am helping a friend.

Is there a way without pointers return number of lines to a const int for use in a for loop?

I know I can do it with pointers but he has not learned them in class yet and I am not morally allowed to teach him anything the professor hasn't.

Example:

int numLines = sizeOfFile(inputFile);
for(int i = 0, i < numLines; i++){
  //code here
}

EDIT: my fault I was moving fast to code this thing. I am helping him today I want to have a finished project so I can work off of it while helping him. The reason I need a constant int is so I can set array to that size not just for a for loop. the array is the problem.

Answer 1

In the simplest case you're just looking for the number of '\n' characters in the file.

So let's say that you've successfully opened the file to: ifstream pFile then you can use an istreambuf_iterator to count those:

const auto numLines = count(istreambuf_iterator<char>(pFile), istreambuf_iterator<char>(), '\n')

A couple comments here:

1. The this count operation will consume everything in pFile's buffer, meaning you'll need to call pFile.seekg(0, ios_base::beg)
2. Picking and choosing values to read from an ifstream indicates a bad smell in code. It's likely that the file format was improperly conceived, or that the program will subsequently need to re-stream the remainder of file contents. The 2^nd option seems to be true in your case, as you seek to illegally set the size of an array with a value found at runtime:

The reason I need a constant int is so I can set array to that size

EDIT:

When you say you want to use numLines to "right an array"_[sic], my assumption is that the only reason that you would have needed your array to be that size is that you're going to stream each line from a file into your container, that is you're going to stream the entire file once to calculate the size then stream the entire file again to populate your container. Here's what you should do instead:

vector<string> lines;

for(string line; getline(pFiles, line);) {
    lines.push_back(line);
}

Now lines will contain your entire file, with each element being a line. If numLines would have been important to you, instead you can use size(lines).

Answer 2

You can initialize a const int just the same as you would initialize a regular int. The difference with a const int is that you cannot re-assign after initialization.

const int numLines = sizeOfFile(inputFile);
for(int i = 0, i < numLines; i++){
  //code here
}