Reading File, Searching, Output

[Sharkolomew]

Hi all. I have a problem

I want my program to do the following.

Create a file of student ID #s.
Then, Read the file.
Search for the line of student ID # say 10002.
At that line, input test scores received from input earlier in program.

Initial file should look like:

10001
10002
10003
10004

After output:

10001
10002 65 45 35 34 //or "65,45,35,3 4" does not matter if there are spaces, commas, etc.
10003
10004

Now, I can create the student ID file fine, But I am not sure how to read and output exactly on that line. I am using fstream, but it seems to erase the whole file when it is finished.

Any help is appreciated. Thank you.

[Sharkolomew]

Any ideas, please?

[r035198x]

Hi all. I have a problem

I want my program to do the following.

Create a file of student ID #s.
Then, Read the file.
Search for the line of student ID # say 10002.
At that line, input test scores received from input earlier in program.

Initial file should look like:

10001
10002
10003
10004

After output:

10001
10002 65 45 35 34 //or "65,45,35,3 4" does not matter if there are spaces, commas, etc.
10003
10004

Now, I can create the student ID file fine, But I am not sure how to read and output exactly on that line. I am using fstream, but it seems to erase the whole file when it is finished.

Any help is appreciated. Thank you.

I hate to ask for code but maybe if you post the code that you think is wrong ...

[Sharkolomew]

sure,

this code represents modifying the student data after the data file contains lines for each student number.

cout<<"Enter student ID # to modify: ";
cin>>studentID;
cout<<"Enter all student scores: ";
cin>>scores;  //this could be either "50 50 50" or "50,50,50" if its easier to read in
fstream f;
f.open("data.txt");
while(f>>input)
{ 
   if (input==studentID)
      {
          cout<<"found";                 //shows that it is finding the student ID
           f<<studentID<<" "<<scores<<end;    //i think the problem is here
      }
}
 

[ilikepython]

sure,

this code represents modifying the student data after the data file contains lines for each student number.

cout<<"Enter student ID # to modify: ";
cin>>studentID;
cout<<"Enter all student scores: ";
cin>>scores;  //this could be either "50 50 50" or "50,50,50" if its easier to read in
fstream f;
f.open("data.txt");
while(f>>input)
{ 
   if (input==studentID)
      {
          cout<<"found";                 //shows that it is finding the student ID
           f<<studentID<<" "<<scores<<end;    //i think the problem is here
      }
}
 

I think you need to open the file in append mode. That way you can add on to it without erasing the whole file. Try this:

f.open("data.txt", ios_base::app);
 

but I'm not sure if that's the way to set it to append mode.
Also, you might want to try using the fseek function. That way you can go to a position in a file.

[Savage]

f.open("data.txt", ios_base::app);
 

but I'm not sure if that's the way to set it to append mode.
.

Yes,that's the way for sure!!!

Nice ilikepython.

Savage

[Sharkolomew]

Okay, my code is no longer disappearing, but it is not putting out the scores still.

How does the fseek function work?

[Savage]

Okay, my code is no longer disappearing, but it is not putting out the scores still.

How does the fseek function work?

first here is declaration: int fseek(FILE *stream,offset, whence);
fseek function works this way:

It sets a pointer assigned to the FILE stream on location in file which depands on offset and whence.Offset represent differance in bytes beetwen whence and new location.Whence represent a file pointer location and have 3 possible values:

SEEK_SET seeks from begining of the file
SEEK_CUR seeks from current location and
SEEK_END seeks from EOF.

Savage

[Sharkolomew]

Well turns out append mode is not what I am looking for. I need to insert or replace text on the current line, not at the end.

To get to the current line, I use while(f>>input) //input is an int\

Once it finds the line, I want to add to that current line and keep the rest of the file intact.

Fseek looks like it may work, but I cant find a relevant example in replacing text when I googled it.