int data from file

**LloydUzari** · 08-05-2004

How could I get int data from a file? Im trying to use files better, as I said on my "checking existance" post, but I ran into another problem completely aside from existance. Im trying to load int data from a txt, but because it is in a char variable I cant use any operations on them. Once again, Im asking if theres a simple way to do this, or if Im gonna have to make another custom function for this, too.

Note: Ive tried the (int) before it, but instead of the same thing, the number is something in the millions

**Perspective** · 08-05-2004

Code:

ifstream in("file");
int foo;
in >> foo;
cout << foo << endl;

**LloydUzari** · 08-05-2004

That didnt work when I tried it, but I found it in the faq anyways:

Code:

char* charnum="376"[4];
int intnum;
intnum=atoi(charnum);

**hk_mp5kpdw** · 08-05-2004

Depends on how you wrote the int to the file:

If written to a file as text:

Code:

//Write int to file
ofstream output("data.txt");
int val = 10;
output << val;
output.close();

//Read int from file
ifstream input("data.txt");
int val;
input >> val;
input.close();

If written as binary data:

Code:

//Write int to file
ofstream output("data.txt",ios::binary|ios::out);
int val = 10;
output.write((char*)&val,sizeof(val));
output.close();

//Read int from file
ifstream input("data.txt",ios::binary|ios::in);
int val;
input.read((char*)&val,sizeof(val));
input.close();

Originally Posted by LloydUzari

That didnt work when I tried it, but I found it in the faq anyways:

Code:

char* charnum="376"[4];
int intnum;
intnum=atoi(charnum);

What does that have to do with file i/o???? Sounds like you were really asking how to convert a character array (string) or string container storing numerical values into an int data type.

**LloydUzari** · 08-05-2004

That was just an example, I took the char variable I got from reading the file, and changed it using that.

**prog-bman** · 08-05-2004

How are you inputing it if it is a number? You should have no trouble doing the methods shown above. Could you show what you are doing it sounds like your making it harder then it really is?

**LloydUzari** · 08-05-2004

Its most likely because of the way Im using. Im using the get subfunc so it will check the whole line instead of just one word, but it doesnt allow using an int variable. I just needed a way to get an int from it, so I think I found it, unless theres a better way :/

Code:

void loadset(const char *filename) {
  char* num1=new char[100];
  char* num2=new char[100];
  char* num3=new char[100];
  int numONE, numTWO, numTHREE;
  int location[5];
  std::ifstream loadline(filename);
  loadline>>location[1];
  loadline>>location[2];
  loadline.seekg(10);
  loadline.get(num1, 100, '\n');
  loadline.seekg(17 + location[1]);
  loadline.get(num2, 100, '\n');
  loadline.seekg(24 + location[2]);
  loadline.get(num3, 100, '\n');
  numONE=atoi(num1);
  numTWO=atoi(num2);
  numTHREE=atoi(num3);
  std::cout<<"Num1: "<<numONE<<std::endl;
  std::cout<<"Num2: "<<numTWO<<std::endl;
  std::cout<<"Num3: "<<numTHREE<<std::endl;
  loadline.close();
}//loadset()

Thats whats there right now. It seems to work well, but it does seem to slow the cout down a bit for some reason. So you know what the file looks like:

Code:

3 5
Num1=376
Num2=29
Num3=2

The numbers at the top tell the program how many extra characters to skip.(Note I did use the >> for the numbers up top cause it seemed easier, but the others Im using like that cause in the accual version I am going to use numbers in some slots, and char in others.)

Note: Thats just to test if its working, currently Im working on an address book like program, and am trying that setup.

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