Opening files with a twist, C++

calculus87 · #1 26-Sep-2003, 08:06

Hello,

Okay, in my program I open a file and begin to put data in the file. Now before I am finished putting the data in the file I need to use some of the data.

okay for example
data in file1:
3 4

Now for the next input I need to take the sum of the first two statements. So the next spot in the statement would be 7

3 4 7

afterwards I go on inputting data.

3 4 7 1 ...

I tried to do a function inside a function, where the outer function opens the file, and begins to input data into it.
Then the inner function is called. It opens the file and takes the
first two inputs, does the conversions, adds them, converts them back then inputs the string into the file then exits.
The outer function then continues inputing into the file.

When I run my code I am supposed to have a=3 and b =4 but they are blank.

so my question is this.
1) can it be done?
2) here is some of the code that I have tried, any suggestions on how to fix this code?

Thanks for the help
~Ronald

CPP / C++ / C Code:

//**********************
int main()
{
fstream scan;
scan.open("calcout.txt", ios::out| ios::in);
output<<"3 ";
output<<"4 ";
output<<getstrings();
output<<"1 "
return 0;
}
//**********************
string getstrings()
{
string a, b;
ifstream input2;
double s1,s2,sum=0;
string t1;
stringstream stream;

input2.open("calcout.txt");
input2>>a;
input2>>b;
cout<<a<<endl<<b<<endl;

s1=atof(a.c_str());
s2=atof(b.c_str());
sum = s1 + s2;

stream << sum;			
t1 = stream.str();
input2.close();
return t1;
}

Garth Farley · #2 26-Sep-2003, 09:44

Hey,

trying to have the same file opened twice and reading & writing simultaneously doesn't work. The file system should only allow you to open a file for writing if no other program is using it.

You'll have to rethink how you store your data - memory would be the handiest for small things.

Is this a very recursive operation? Will you need to go back & forward through a text file a lot? There are functions like seekg() where you can move the file pointer back & forward, but writing & reading simultaneously is still a problem.

GF

calculus87 · #3 26-Sep-2003, 14:41

What you have said makes great sense. I will try to use the seekg function. Thank again
Sincerely,
Ronald

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