Thread: C++ input

Code:

  #include <iostream>
 #include <fstream>
 #include <math.h>

 using namespace std;
 int main()
 {
   
    char str[2000];
    fstream file_op("C:\\IndusCommodities\\PriceFiles\\AllMarkets-1.txt",ios::in);
    if (!file_op.is_open())
    {
  
              cerr << "Unable to open the file" << endl;
              return -1;

          }
       while(!file_op.getline(str, sizeof(str)))
       {
               cout <<str;
         }
  
          file_op.close();
  
          cout <<endl;
   
  
          return 0;
  
      }

I am trying to read in a text file and print out the result. The program compiles and executes fine, but nothing comes on the screen.

Originally Posted by heathrowjohnny

I am trying to read in a text file and print out the result. The program compiles and executes fine, but nothing comes on the screen.

The main problem is that basic_ios::operator! will return true when the stream is bad, and false otherwise. So your while condition is backwards.

Other things:

Don't use a statically-allocated char array for things like this. Although the second parameter of getline will prevent a buffer overflow, it would be much better to use C++ style strings here (you will need to use the global getline function, defined in <string>). Also, keep in mind it is usually poor style to dump the entire std namespace like that, but for a tiny program like this there isn't a problem. And it is not necessary to call file_op.close at the end, because the fstream destructor will do it automatically.

I would rewrite it as:

Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
  fstream file_op("C:\\IndusCommodities\\PriceFiles\\AllMarkets-1.txt", ios::in);

  if(!file_op.is_open())
  {
    cerr << "Unable to open the file" << endl;
    return -1;
  }

  string line;
  while(file_op && !file_op.eof())
  {
    getline(file_op, line);
    cout << line << '\n';
  }

  return 0;
}

<math.h> isn't needed here, but if you are going to use it, I suggest using <cmath> instead, since everything will be placed in the std namespace that way.

thanks. I was using <math.h> because I will need it later. Yeah I am just learning C++ but know some Java.