Problem with creation of files

[DannyPt]

i am doing a program where i have to create a file, witch i have to ask where to save, the name, and the extension, and then it have to be writing wat i want for the all program, but at the end i have a question about want to leave the program or not, if this anwer is to get out of the program i want him to get out of the program and save the file, but if the answer is to continue in the program i want him to continue writing withou deleting anything...
i looked in this website:
http://www.mattjustice.com/cnotes/c_fileio.html
but the program allways delete the contents of the file
this is the part thtat creates the file in my program:

FILE *f;
if(f != NULL)
	{
		f=fopen("c:\\euromilhoes.txt","r+");
        }
else
	{
		f=fopen("c:\\euromilhoes.txt","w");
	}

this file is allways created in the beggining of the program...
if anyone can help me, i would be thankfull

[JLBorges]

Is this what you intended?

std::FILE* f = std::fopen( "c:\\euromilhoes.txt", "r+" ) ;
if( f == nullptr ) f = std::fopen( "c:\\euromilhoes.txt", "w" ) ;
if( f == nullptr ) { /* give up */ } 

[DannyPt]

what will that do? is to only writte in the file and to not delete wat is in it?

[JLBorges]

Line one tries to open an existing file for reading and writing.
If that does not work ( f is null ) line two tries to create a new file.

Ckeck out std::FILE* f = std::fopen( "c:\\euromilhoes.txt", "a+" ) ;
http://www.cplusplus.com/reference/clibrary/cstdio/fopen/
That may be just what you need.

Note: In the original code,

std::FILE *f ; // f is an uninitialized pointer
if( f != NULL ) // you can't use f meaningfully till after it is properly initialized  

[DannyPt]

i allready saw wat was wrong... in the website that i got it didnt meantion the "a+" and that is the solution... tks.

now how can i ask to the user to tell where to create the file and how to call it? because i cant put something like:
f=fopen("%c:\\euromilhoes.txt", driver,"a+");

[JLBorges]

> now how can i ask to the user to tell where to create the file and how to call it?

I'm not sure I understand that question.

[DannyPt]

will i am running the program, the program should ask the user in whwat driver and what the name of the file to be created.
something like this:

Wich is the drive of the file?
>
Wich is the file's name?
>

now i saw one problem... the file euromilhoes.txt that i did in f=fopen("%c:\\euromilhoes.txt", driver,"a+");
now i cant delete it... do you know why?

[megazord32]

well, i'm with the same doubt.

The program should ask:

Wich is the drive of the file?
>
Wich is the folder of the file?
>
Wich is the file's name?
>

How do I do that?

[JLBorges]

Use a std::string to hold this information. http://www.cprogramming.com/tutorial/string.html

char drive_letter ;
std::cout << "Wich is the drive of the file? " ;
std::cin >> drive_letter  ;

std::string path_to_folder ;
std::cout << "Wich is the folder of the file? " ;
std::cin >> path_to_folder ;

std::string file_name ;
std::cout << "Wich is the file's name? " ;
std::cin >> file_name  ;

std::string full_path_to_file = drive_letter  + "\\" + path_to_folder  + "\\" + file_name  ;
std::FILE* f = std::fopen( full_path_to_file.c_str(), "a+" ) ;
if( f == nullptr )
{
    std::cerr << "file name '" << full_path_to_file << "' is invalid\n" ;
    // ...
}

[DannyPt]

isnt there another way to do it? because i dont understand nothing about strings and i when i insert your program into mine it just give me errors

and i really dont understand all of that cout and cins... never used that, and in my all program i am using printf and scanf, is it possible to substitute?

[JLBorges]

> i dont understand nothing about strings ...
> and i really dont understand all of that cout and cins ...

It is perfectly fine that you do not understand something at this moment; folks here would be very willing to help you understand. But you have to make an effort to try and understand C++.

If you are unwilling to do that, perhaps you should post your questions on a C board. I've been told that this is a fairly good one: http://cboard.cprogramming.com/c-programming/

[DannyPt]

but isnt in C that it work with the cout and cin insted of the printf and scanf?

[Moschops]

No. C++ works with cout and cin. C does not.