clear EOF doesn't work

Write your question here.

  ifstream fin(filename);

double s;
int count=0;
	while(1){
		fin>>s;
		count=count+1;
    if (fin.eof()) {fin.clear(	);		                
		   break;
	            }
	         }

    for (int k=0; k<ndata-1;k++){
			cout<<k<<endl;
      fin>>data[k];
      if (fin.eof()){
        cout<<"End of file reached exiting"<<endl;
	exit(1);
                    }

                                }

I want read data from file and put them in data vector. But I want to check the vector size.I can not "clear" the bit eof so that if I check it doesn't fill the vector and jump do cout<<"End of file..."

Ganado (6786)

(1) Your indentation is messed up because you're mixing tabs and spaces.
(2) Using eof is often error prone if you aren't using it in a valid place. You should instead be checking the success of the extraction of a number instead.
(3) If the file stream is at its end, calling fin.clear() only resets the failbit. It doesn't reset the file offset.
(4) Why ndata - 1? Possible "off-by-one" fencepost error.

What does your file look like? Why are you looping over your file twice?
<edit: I assume you are iterating it the first time simply to get the count of numbers. But why? If you don't know the size of an array at compile-time, you should be using a vector anyway.>

If your file looks like: 42 3.14 2.78 ... and you know the maximum number of elements, you can do something like:

const int MaxSize = 1000;
double arr[MaxSize];
int size = 0;

double num;
ifstream fin(filename);
while (fin >> num && size < MaxSize)
{
    data[size] = num;
    size++;
}

Last edited on

seeplus (6474)

To read numbers from a file into a vector is as simple as :

1
2
3

std::vector<double> data;

for (double item{}; fin >> item; data.push_back(item));

Why do you need to check the size of the vector? To know how many numbers have been read use:

data.size();

Handy Andy (5051)

Hello stefano77,

I do not know what you are using to write your code in, but an example of what could be done. The comments should explain most of it:

ifstream fin(filename);

double s;
int count = 0;

while (1)
{
    fin >> s;

    count = count + 1;

    if (fin.eof())
    {
        fin.clear();  // <--- Resets the state bits, but leaves the file pointer at the end.
        break;
    }
}

for (int k = 0; k < ndata - 1; k++)
{
    cout << k << endl;

    fin >> data[k];

    if (fin.eof())  // <--- Abetter choice "if (!fin)". Checks more than just "oef" bit".
    {
        cout << "End of file reached exiting" << endl;

        exit(1);  // <--- If this is in "main" use return not "exit()". Actually never use "exit()".
    }

}

"exit()" is a C function. It works, but it does not know about classes or about cleaning up anything before a program ends. "exit()" is an unconditional exit from the program and has the potential for problems. You should favor return except in some rare cases.

Andy

George P (5610)

Why you should not use exit() in main:
https://stackoverflow.com/questions/461449/return-statement-vs-exit-in-main

C++* has two macros for returning success or failure. Use those with a return statement:
https://en.cppreference.com/w/cpp/utility/program/EXIT_status

*The macros are actually in a C library, they work in C++ also.

#include <cstdlib>

int main()
{
   return EXIT_FAILURE;
}

The program ends with a status code of 1.

Topic archived. No new replies allowed.

C++

Forum

clear EOF doesn't work