How to determine number of lines in a text file to return an array

[CK938]

Hi,

I'm new to C and I'm trying to read in a file that can have an arbitrary number of lines, and put each line into a string array. I guess my problem is that I dont't want to have to explicitly create a new array with a certain size since the number of lines can always change (in the code below I use 101). Is there a better way to return an array or a pointer to an array that contrains all the lines. This is what I have so far.

 
string* test()
{    
    string line;
    string *vol= new string[101];
    int i = 0;
 
    ifstream myfile("VOL.txt", ios::in);
 
    if (myfile.is_open())
    {
        while(!myfile.eof() && i != 101)
        {
            getline (myfile, line);
 
            if (line != firstLine)
            {
                vol[i] = line;
                i++;
            }
        }
        myfile.close();
    }
 
    return vol;
}
 

[archonmagnus]

You will have to read the entire contents of the file first. You could insert a section of code like the following:

// ... previous code
 
if (myfile.good())
{
    do
    {
        myfile>>char;
        if (char == '\n') lines++;
    } while (!myfile.fail());
 
    myfile.clear()   // resets the EOF bit so the file can be read again
    myfile.seekg(0);  // make sure the "get" pointer is at the beginning of the file
 
    string *vol= new string [lines];
 
    // ... trailing code follows
}
 

[scruggsy]

Or, use a vector instead of an array, and just push each new line onto the vector as it's read, letting the vector take care of resizing itself if needed.

[weaknessforcats]

You are using C++. Arrays are low-level containers that C++ has inherited from C and you are coming up against the first problem with arrays: they are fixed.

In C++ use a vector<string>.

As you add strings to the vector it expands. So you just read the the lines from your file and do a push_back() for each line. No need to read the file and count lines, etc.

[CK938]

Thanks for all your help. I think I got it.