How to open file?

Hello, I am a beginner. I read this page already, but just one things that I don't understand. How to open the example.txt when i type open? And the code below is the whole code.

Code:

---

#include <fstream>
#include <iostream>

using namespace std;

int x ;
char y ;
char op ;

int main()
{
    int x ;
    char y[1000] ;
  char str[10];
  char op [5] ;

  //Creates an instance of ofstream, and opens example.txt
  ofstream a_file ( "example.txt" );
  // Outputs to example.txt through a_file
  cout<<"type some numbers :";
  cin>> x ;
  a_file<<"number :" <<x ;
  cout<<"type some alphabet :";
  cin>> y ;
  a_file<<"alphabet: "<<y ;
  cin.ignore();
 
  // Close the file stream explicitly

  a_file.close();
 
  //Opens for reading the file
  ifstream b_file ( "example.txt" );
  //Reads one string from the file
  b_file>> str;
  //Should output 'this'
  cout<< str <<"\n";
  cin.get();    // wait for a keypress
  // b_file is closed implicitly here
}

---

You want to open the file but only when the user types "open"? Seems you'll need some kind of input processing loop that asks the user for a command and handles the options that the user enters. You can prompt the user and read their choice into a std::string variable. After that, it's just a series of if/else-if constructs to determine what the user entered and to execute the desired functionality.

I also tried that, but i don't know to check weather the user type open to open the file. I tried this:

Code:

---

char op[6] ;//i put this after using namespace std;
/////////////////////////////////////////////////////////////////
char op[6] ;// i put this after the int main(){
///////////////////////////////////////////////////////////////
cin>> op ;
if  ( op = 'open' ) {
cout<<"this is to test weather the code right ..." ;
}

---

but it gave me error: 32 G:\ccc\dllmain.cpp incompatible types in assignment of `int' to `char[6]'
i can't figure out how to fix it.

Use double quotes for a string, and use == for comparing if equal. One = means "assign".

--
Mats

Code:

---

cin>> op ;
if  ( op == "open" ) {
cout<<"this is to test weather the code right ..." ;
}

---

the error didn't come out again but the message didn't show up even i type open.

use strcmp to compare string, don't use ==

Code:

---

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char *argv[])
{

    int x ;
    char y[1000] ;
    char str[10];
    char op [5] ;

    cout << "Wait for input: ";
    // get input, if the input is not "open", wait for another input
    while (true) {
        cin >> op;
        if(strcmp(op, "open")== 0) break;
        else cout << endl << "Hint: open" << endl << "type again:" ;
    }

   
    //Creates an instance of ofstream, and opens example.txt
    ofstream a_file ( "example.txt" );
    // Outputs to example.txt through a_file
    cout<<"type some numbers :";
    cin>> x ;
    a_file<<"number :" <<x ;
    cout<<"type some alphabet :";
    cin>> y ;
    a_file<<"alphabet: "<<y ;
    cin.ignore();
   
    // Close the file stream explicitly
   
    a_file.close();
   
    //Opens for reading the file
    ifstream b_file ( "example.txt" );
    //Reads one string from the file
    b_file>> str;
    //Should output 'this'
    cout<< str <<"\n";
   
    system("pause");
}

---

Quote:

---

Originally Posted by w.chen

use strcmp to compare string, don't use ==

---

or even better - do not use C-strings, use std::string instead

Yea, thanks w.chen. But if i want to open the output file when i type open, does that possible?

I don't understand what do you mean "open the output file", if you mean open it using some sort of texteditor, you can call system("command") to do it. e.g. system("notepad.exe example.txt")

if you want to open the file and do something with it in your c++ program, using ofstream and ifstream as the code you've provided.

if you mean just type open (without enter) to open the file, it is possible but I won't suggest you to do so.

Quote:

---

Originally Posted by w.chen

use strcmp to compare string, don't use ==

---

Code:

---

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char *argv[])
{

    int x ;
    std::string y;
    std::string str;
    std::string op;

    cout << "Wait for input: ";
    // get input, if the input is not "open", wait for another input
    while (true) {
        cin >> op;
        if (op == "open") break;
        else cout << endl << "Hint: open" << endl << "type again:" ;
    }

   
    //Creates an instance of ofstream, and opens example.txt
    ofstream a_file ( "example.txt" );
    // Outputs to example.txt through a_file
    cout<<"type some numbers :";
    cin>> x ;
    a_file<<"number :" <<x ;
    cout<<"type some alphabet :";
    cin>> y ;
    a_file<<"alphabet: "<<y ;
    cin.ignore();
   
    // Close the file stream explicitly
   
    a_file.close();
   
    //Opens for reading the file
    ifstream b_file ( "example.txt" );
    //Reads one string from the file
    b_file>> str;
    //Should output 'this'
    cout<< str <<"\n";
   
    system("pause");
}

---

It's truly amazing how people come into the C++ forum and offer C-style solutions...

Quote:

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f you want to open the file and do something with it in your c++ program, using ofstream and ifstream as the code you've provided.

---

Do you mean this code:

Code:

---


f you want to open the file and do something with it in your c++ program, using ofstream and ifstream as the code you've provided.

---

or this:

Code:

---

a_file.close();
   
    //Opens for reading the file
    ifstream b_file ( "example.txt" );
    //Reads one string from the file
    b_file>> str;
    //Should output 'this'
    cout<< str <<"\n";

---

after the user type some numbers and alphabet , it will make a notepad with name : example.txt . If the user type "open" and pressed enter, i want it to open the example.txt.

Ok, now i saw a code like this:

Code:

---

#include <stdio.h>
#include <iostream>

using namespace std;


int main ()
{
  FILE * pFile;
  pFile = fopen ("myfile.txt","w");
  fopen ("myfile.txt","r");
  if (pFile!=NULL)
  {
    fputs ("fopen example",pFile);
    fclose (pFile);
    cin.ignore();
  }
  return 0;
}

---

i tried ran this program, but nothing opened, why?
I want to sure weather the fopen got error or the location is unspecific enough?

1) This is the C way. This is way you do in C, not C++.
2) And, it's open in read-only mode. Meaning no writes can be done on the file.

Quote:

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Originally Posted by Elysia

2) And, it's open in read-only mode. Meaning no writes can be done on the file.

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It opens same file twice - first for writing, then for reading (without storing the pointer to the file)

Ah, that's true too. I missed that... :(

I just open the c++ and then in the file tab, i select the source file in the new
or in other word just use ctrl + n(hotkey) and after this i paste this code. Does this code still usable? I know the 'r' is open for read and 'w' is open for write, but i just want to know how to open it?