problem with opening file function in c++

tinieprotonjam · 02-14-2007, 07:53 AM

/*I am currently programming in Linux using the g++ compiler. I was trying to make an open function that would open a file and store its contents in a 2d vector. I was successful at doing the said function. I thought I was done with it, but I realized that I can sucessfully call the function once in the prgrogram, whenever I call it again, it would not open any file. So I thought there might be wrong with my implementation, so i just just opening a file and then just output it to the screen, only one file is sucessfully opened and only one output is shown. Here's the code, can anybody help in pinpointing the problem.

here's the code I did, trying to find out what's wrong, I was only prompted to enter the filename once, then the next one somewhat bypassed...

Code:

//try.cpp
#include <iostream>
#include <fstream>
using namespace std;

char filename[20], new_file[20];
fstream is;
int openFile(char file[20]){
char c;
if (is.open (file)){        // open file

  while (!is.eof())     // loop while extraction from file is possible
  {
    c = is.get();       // get character from file
    cout << c;
  }

is.close();           // close file}
else cout<< "error opening file";
return 0;
}


int main () {
  //char c, str[256], newfile[256];
  

  cout << "Enter the name of an existing text file: ";
  cin.get (filename,20);
  openFile(filename);

cout << "Enter again the name of an existing text file: ";
cin.get (new_file,20);
openFile(new_file);
  return 0;
}

here's the output, after compiling this using g++ -o try try.cpp:

[root@192~]# ./try
Enter the name of an existing text file: file01.txt
new file
ito
hahahaÿEnter again the name of an existing text file: [root@192~]

the program will not let me type the filename of the next file that I want to open...
I hope someone would be able to help me....thanks in advance....

xhi · 02-14-2007, 09:40 AM

ignoring the syntax errors (probably a copy/paste error?), you have a couple logical errors.

a. cin.get leaves the delimiting char on the stream. so after you get the first string the new line is extracted by the second cin.get call leaving you with an empty second string. (see some documentation on istream::get)

b. when you open an fstream, read it to the end, close it, and open it again for reading, you have to call clear() to clear the error flags. otherwise the eof (and other) error flag is still set from the first open, read, eof, close sequence.

PS. a better solution for a. (among others) would be istream::getline()

tinieprotonjam · 02-14-2007, 09:48 PM

Quote:

Originally Posted by xhi

ignoring the syntax errors (probably a copy/paste error?), you have a couple logical errors.

a. cin.get leaves the delimiting char on the stream. so after you get the first string the new line is extracted by the second cin.get call leaving you with an empty second string. (see some documentation on istream::get)

b. when you open an fstream, read it to the end, close it, and open it again for reading, you have to call clear() to clear the error flags. otherwise the eof (and other) error flag is still set from the first open, read, eof, close sequence.

PS. a better solution for a. (among others) would be istream::getline()

regarding the syntax errors, i mistakenly posted the unedited code, but I was able to fix it... secondly, I added the call to clear after closing the file and then used iosteam::getline instead of iostream::get, and the problem was solved... thanks a lot...