Programming Forums > Application Development > C++

Syntax_Error · Jan 19th, 2008, 5:05 PM

I'm unsure exactly how to do file I/O in C++. I've been googling and found that fstream should do the trick, but when I start to use some tutorials, Dev-C++ complains about depreciated or antiquated headers. Can someone write up a little basic example of how I/O works. Like actually open an example text file and write to it or something. Just need something I can chuck into Dev-C++ and see if it still complains at me.

-Syntax_Error

grumpy · Jan 19th, 2008, 5:11 PM

(Toggle Plain Text)

#include <iostream>   // basic iostream functionality
#include <fstream>    // file streams

int main()
{
    std::ofstream output("x.dat");
    output << "You are using old material\n";
    output.close();       // optional, fstream's implicitly closed as object is destructed
}

This will create a file named x.dat in the current working directory of your application .... wherever that is.

Syntax_Error · Jan 19th, 2008, 5:17 PM

Awesome, thanks. Worked well.

Now, with that out of the way, how would one go about opening said file back up, reading and looking for contents and if certain "settings" are set, altering code based on that.

for example... say I'm trying to do a simple "To-Do" application with flat file databasing for my "tasks"... how do I pull those back out, maybe sort based on a priority number or something, and show them to me. I can probably figure out how to edit/delete.

Game_Ender · Jan 19th, 2008, 11:29 PM

You need to come up with your own file format. You can write and read int, doubles, and std::strings from the file. Don't have time to give a code example but a typical format is:



[Section]

Key = Value

Key2 = Value



[Section2]

Key = Value

Ancient Dragon · Jan 19th, 2008, 11:55 PM

Quote:

Originally Posted by Syntax_Error

for example... say I'm trying to do a simple "To-Do" application with flat file databasing for my "tasks"... how do I pull those back out, maybe sort based on a priority number or something, and show them to me. I can probably figure out how to edit/delete.

There are millions of ways to do that, but I would read/write binary structures because that is very fast. Reading/writing to text files is slooooow, but is ok if you don't want to do it very often.

(Toggle Plain Text)

struct data
{
    int a,b,c;
    char name[80];
    char something_else[80];
};
data array[16];
// now write a bunch of structures to a file
ofstream out("outfile.dat", ios::binary);
out.write(array, sizeof(array));

// read the array back into memory
ifstream in("outfile.dat", ios::binary);
in.read(array, sizeof(array));

There are lots of things you can do with the above, such as write them all out at one time as I did then read them back one at a time in random order if you want. The file is also very easy to update -- no need to rewrite the entire file like you have to do with text files.

The bad thing about the binary format illustrated above is that it is very difficult to change the file format. Lets say I want to add or remove something from that structure. To do that you would need to write a file conversion program that converts the data from the original structure format to the new one.

Jan 19th, 2008, 5:05 PM	#1
Syntax_Error Programmer Join Date: Jan 2008 Posts: 9 Rep Power: 0	C++ File Input/Output Assistance Please I'm unsure exactly how to do file I/O in C++. I've been googling and found that fstream should do the trick, but when I start to use some tutorials, Dev-C++ complains about depreciated or antiquated headers. Can someone write up a little basic example of how I/O works. Like actually open an example text file and write to it or something. Just need something I can chuck into Dev-C++ and see if it still complains at me. -Syntax_Error

Jan 19th, 2008, 5:11 PM	#2
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	Re: C++ File Input/Output Assistance Please (Toggle Plain Text) #include <iostream> // basic iostream functionality #include <fstream> // file streams int main() { std::ofstream output("x.dat"); output << "You are using old material\n"; output.close(); // optional, fstream's implicitly closed as object is destructed } #include <iostream> // basic iostream functionality #include <fstream> // file streams int main() { std::ofstream output("x.dat"); output << "You are using old material\n"; output.close(); // optional, fstream's implicitly closed as object is destructed } This will create a file named x.dat in the current working directory of your application .... wherever that is.

Jan 19th, 2008, 5:17 PM	#3
Syntax_Error Programmer Join Date: Jan 2008 Posts: 9 Rep Power: 0	Re: C++ File Input/Output Assistance Please Awesome, thanks. Worked well. Now, with that out of the way, how would one go about opening said file back up, reading and looking for contents and if certain "settings" are set, altering code based on that. for example... say I'm trying to do a simple "To-Do" application with flat file databasing for my "tasks"... how do I pull those back out, maybe sort based on a priority number or something, and show them to me. I can probably figure out how to edit/delete.

Jan 19th, 2008, 11:29 PM	#4
Game_Ender Professional Programmer Join Date: May 2006 Location: Maryland, USA Posts: 306 Rep Power: 3	Re: C++ File Input/Output Assistance Please You need to come up with your own file format. You can write and read int, doubles, and std::strings from the file. Don't have time to give a code example but a typical format is: `[Section] Key = Value Key2 = Value [Section2] Key = Value` __________________ Robotics @ Maryland AUV Team - Software Lead

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Programming Forums > Application Development > C++

C++ File Input/Output Assistance Please