fstream trouble

[Daniel Riddle]

I'm getting a runtime error that i cant interpret. EXC_BAD_ACCESS. Please Help. The .txt file is a list of number like so:
56
78
90
99
87
45

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
using namespace std;


int main(int argc, const char * argv[])
{
    vector <int> gradeVector;
    int Input=0, runnTotal=0;
    ifstream gradesDoc ("/Users/DPRiddle/Documents/School 2013/C++/Grades.txt" );
        while (! gradesDoc.eof())
            {
                gradesDoc >> gradeVector [Input];
                cout << gradeVector[Input]<<endl;
                runnTotal += gradeVector[Input];
                Input++;
            }
        gradesDoc.close();
    cout << "The average grade was:" << runnTotal/ Input<< endl;

    return 0;
}

[Cubbi]

this creates an empty vector
vector <int> gradeVector;

This writes into the Input'th element of the empty vector, which doesn't actually exist, so it writes to some other variable's memory, or maybe over your function's return address, memory you don't own, etc.
gradesDoc >> gradeVector [Input];

To append a value to the vector, us push_back (and, while at it, stop using .eof())

#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
    ifstream gradesDoc ("/Users/DPRiddle/Documents/School 2013/C++/Grades.txt");

    vector <int> gradeVector;
    double runnTotal=0;
    int value;
    while (gradesDoc >> value)
    {
        gradeVector.push_back(value);
        runnTotal += value;
    }
    cout << "The average grade was:" << runnTotal/gradeVector.size()<< '\n';
}

[ne555]

You are accessing the vector out of bounds.
To insert an element you may use push_back()

[jlb]

Before you can access a vector element with the array notation[] the element must already exist. You may want to look a the documentation for vector and look at the vector.push_back() member function.

Jim

[tfityo]

Try rewrite this

                
                gradesDoc >> gradeVector [Input];
                cout << gradeVector[Input]<<endl;
                runnTotal += gradeVector[Input];
                Input++;

into

     
                int t;
                gradesDoc >> t;
                gradeVector.push_back(t);
                cout << t <<endl;
                runnTotal += t;               

[SamuelAdams]

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
using namespace std;


int main(int argc, const char * argv[])
{
    vector <int> gradeVector;
    int Input=0, runnTotal=0;
    int datain;
	ifstream gradesDoc ("/Users/DPRiddle/Documents/School 2013/C++/Grades.txt" );
    
    if(gradesDoc.is_open())
    {
    while (! gradesDoc.eof())
        {
		gradesDoc >> datain;
		gradeVector.push_back(datain);
        cout << gradeVector[Input] <<endl;
        runnTotal += gradeVector[Input];
        Input++;
    	}
        gradesDoc.close();
	cout << "The average grade was:" << runnTotal/ Input<< endl;
    }
    else
        {cout << "File not open" << endl;}

    return 0;
}

[Daniel Riddle]

ah. thanks. that works. cubbi: why stop using .eof?
and while your answering questions: the only way i could get the program to find the .txt file was to put in the file path, but i rarely see file path in sample code of this nature. is there someplace i can put the document that the compiler will look for it automatically?


ifstream gradesDoc ("/Users/DPRiddle/Documents/School 2013/C++/Grades.txt" );

[Daniel Riddle]

With corrections.

int main(int argc, const char * argv[])
{
    vector <int> gradeVector;
    int Input=0, runnTotal=0;
    ifstream gradesDoc ("/Users/DPRiddle/Documents/School 2013/C++/Grades.txt" );
    if (gradesDoc.is_open()){
    while (gradesDoc >> Input)
    {
        gradeVector.push_back(Input);
        cout << Input<<endl;
        runnTotal += Input;
    }
    cout << "There were " << gradeVector.size() << " grades." << '\n'<< "The average grade was:" << runnTotal/gradeVector.size();
        gradesDoc.close();
    }
    else cout << "Unable to open file" << endl;

    return 0;
}

[Olysold]

You can place it in the folder where your project and .cpp files are. Then you can just use "Grades.txt".

[Daniel Riddle]

well thats what i thought, but the program can't find the file when i place it there and delete the file path.

this fails.

ifstream gradesDoc ("Grades.txt" );

all i did was delete the file path.

it should probably be noted i'm using a mac.

[Cubbi]

why stop using .eof?

Because it's an error to use it that way, for two reasons: First, it doesn't predict the future: it's still false at the end of file, it's only true after you attempted, and failed, to read past the end. Second, if you have a non-digit in the file, the input operation will fail with syntax error, and you will find yourself in an endless loop.

is there someplace i can put the document that the compiler will look for it automatically?

In the current working directory of your program. Where it is depends on the manner in which you're running your program (for a notorious example, Visual Studio uses different paths for debug and release builds). Mac is a unix environment, so the normal usage would be to put your program in directory listed in PATH, open a shell window, nagivate to the data file, and run the program (which would be found in PATH) while in that directory.