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 (6813)

(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 (6598)

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

deleted account xyzzy (5768)

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.

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clear EOF doesn't work