.txt file to std::string

I'm trying to get a string to copy everything on a .txt file. I don't care about returns or anything fancy, I just need everything ever typed on the file.

Here I have a .txt file called Default.txt.

x:-100
y:-30
z:30
w:100

It is in a folder located in my project folder, where I keep all my .cpp and .h files.

Macintosh HD/.../Project/Text_Files/Default.txt

Here is my code for putting it into a string (well, technically it's not my code).

using namespace std;

string TextFileToString(string filename)
{
    string line;
    stringstream dosString;
    ifstream inFile;
    inFile.open (filename.c_str());

    while(std::getline(inFile, line))
    {
        dosString<<line<<"\r\n";
    }

    return(dosString.str());
}

// In my main function

string s = TextFileToString("Default.txt");
cout << s;

Why won't this work? I've looked up several other solutions and they all are something like this. Is it because the file path needs to be more than "Default.txt"? I don't know. Please help!