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I am trying to output to a certain line in a file using ofstream. My file is automatically loaded with certain numbers, and I need to exchange one number at a time. For example, it originally outputs:
2400
0000
0000
0000
2500
0000
0000
0000
and I need to change it to:
2400
0000
0000
0000
2500
0000
1700
0000
I originally thought to use seekp, but I cannot seem to make it work correctly. Any ideas?
If your line data is always of a fixed size then you can calculate an offset to use with seekp and jump to a given line and then overwrite the existing data at that location.
If your having issues with seekp then we'd need to see some code to determine if you're using it correctly or not.
Im in the middle of adjusting it right now, so I can't print it right now. I can give more details though. Basically I am trying to use an employee ID to keep track of a clockin/clockout/overtime. Since ofstream likes to create a file all the time, it was wiping my data file during every run. So I decided to copy the data to another file, then rename it to the old file after I am done adjusting it.
employee IDs are 8 characters long. (ie 24001000). The following three lines are default at 0000. Then the next ID number is listed. I want my program to be able to recognize the ID and then print the changes on the correct line below the ID. So:
(ID: ) 24006100
(Overtime: ) 0000
(Time In: ) 0000
(Time Out: ) 0000
If the employee clocks in at 5PM, I want to save that data. So:
(ID: ) 24006100
(Overtime: ) 0000
(Time In: ) 1700
(Time Out: ) 0000
I was using the site seekp - C++ Reference to try to figure out how to use seekp/tellp. I've never used it before, so I am trying to manipulate the formula there to suit my needs.
Do you have a question?Quote:
Originally Posted by Zinsky
My question is if tellp can be used for my situation. And if so, how do you manipulate tellp to go down lines rather than forward character lengths.
tellp tells you current position.Quote:
Originally Posted by Zinsky
you do not "manipulate tellp"
you can use getline to read whole line from the file and then - use tellp to learn the current position...
in that way you can learn at what positions end each line of the text file...
You can use getline 4 or 5 times to read and process a single employee's set of data and after each set of read ops you could use tellg (not tellp) to determine where you are. If you've just read the user whose data you need to manipulate (check the employee id), you can then back up an appropriate amount (use seekp and some subtraction) to get to the proper place. You can then write your new data. This all depends on the employee data all being fixed length and you opening your file in read/write mode.
Or... load everything in the file into memory using an STL container (vector/linked list/etc...) and manipulate it there. After each manipulation of the data in memory - or once at the end of the program - you can flush the changed data to the file overwriting what was there.
[edit]Or maybe seekp/seekg and tellp/tellg can be used interchangeably I'll need to look into that.[/edit]
you will be working with a small amount of data and memory wont be a problem so lets not try to over thinnk the problem mmm kay? There is no advanced functions for files that are messed up or anything fancy like that, you write it. I am not sure about the extra three zeros or wierd stuff, So i am gonna go with it. K?
Just do this and you will be happy happy joy joy ok?
struct employees{
unsigned int id, ot, in, out;
};
list<employees> empdata;
bool load(){
ifstream file("employe.dat");// this will open it in text mode, dont do binary , you dont need it
if(!file) {
cout<<"cannot find file"<<endl;
return false;
}
emploees temp;
while(file){// while we have not reached the end of the file and its state is still Goood
file>>temp.id>>temp.ot>>temp.in>>temp.out;
empdata.insert(temp);
}
file.close();
return true;
}
bool save(){
ofstream file("employe.dat");// this will clear the file by default but it doesnt matter unless you are writing MASSIVE amounts of data, like more than 10 to 20 megs. Even then the difference inst noticeable, maybe a second more to save
if(!file) {
cout<<"cannot open file"<<endl;
return false;
}
for(list<employees>::iterator beg(empdata.begin()); beg!= empdata.end(); ++beg){
file<<beg->id<<beg->ot<<beg->in<<beg->out;
}
file.close();
return true;
}
[code][/code] tags... :rolleyes:
Hi,
I'm trying to use a function to write information to a file.
Let's say I have a function called WriteStuff that will simply print the line number on each line.
In main, I have a ofstream object called OutPutFile.Code:
void WriteStuff()
{
cout <<"Line 1" << endl;
cout <<"Line 2" << endl;
}
How can I use OutPutFile and store the information from the function in a file?
Code:
int main()
{
ofstream OutPutFile;
OutPutFile.open("StoreText.txt");
OutPutfile << WriteStuff();
// I dont know if this is correct
return 0;
}
Thanks
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A bit off topic, but ok...
If you want to use a function that way with chars I am assuming someone else may have a better way I am sure but you could return a char * and save it that way...
Remember to delete foo when you are done with it though...Code:
char *WriteStuff()
{
char *foo;
foo = new char[LENGTH];
strcpy(foo,"I AM A STRING!");
return foo;
}
int main()
{
ofstream save;
save.open("blah.txt");
save<< WriteStuff();
}