read from file to array. about fin.eof() \n EOF...

source file:
1,2
2,5
3,7
4,9
5,11

Code:

int readin(_tag_xandy data[100], ifstream & fin,  int & n)// read data from file function
{
	
	char tmpchar;
  
	while (!fin.eof())
	{
		
		fin>>data[n].x>>tmpchar>>data[n].y;
		
        cout<<data[n].x<<','<<data[n].y<<endl;
			++n;		 
		//cout << "what is n??"<<n<<endl; 
		   //for dubugging
	}
    
	
	//if(data[n].x==NULL||data[n].y==NULL)		
		//return n-1;
	//else 
		return n ;
	//cout<<"after n=n-1...~~n="<<n<<endl;
}

output:

1,3
2,5
3,7
4,9
5,11
0,0

This function is to read from a text file, the output is generated of the struct of arrays in another function.

As you can see, the source file dont contain that group of number 0,0

which appear in the output.

Rest of the codes are okay, I think something cause the difference.

Could u help me out?How to change the codes???Thanks.



The red part may the causes. The cursor in the source file is not just at the end of the file.

read FAQ why you should not use feof to control loop

It should be like this:

Code:

while(fin>>data[n].x>>tmpchar>>data[n].y)
{

2,5
4,9
5,11


Here is the new result, still ....not right

i hope it works and reger to the FAQ,

i still not understand why for this case now work well

Originally Posted by hth373737

2,5
4,9
5,11


Here is the new result, still ....not right

it seems you have leaved the fin>> line inside the loop as well

you need only one read per iteration

Originally Posted by vart

it seems you have leaved the fin>> line inside the loop as well

you need only one read per iteration

Ye,,,

that is it.

but could you explain why this happen? how the statement work?

i cannot understand that statement, as well as the FAQ

Thanks!

Originally Posted by vart

it seems you have leaved the fin>> line inside the loop as well

you need only one read per iteration

what is the terminate condition of that while statement?

how that happen?

why if i add that fin>> line twice, number 1 and 3 group are to be eaten?

confusing

the eof flag is set as a result of the failed operation.

it means - BEFORE failure it is always false.

AFTER failaure - you will chekc it on the next iteration only.

Instead you should check the return value of th eread operation - and if it fails - do not enter the loop

for istreams
if(istr >> x)

is a standard way to check that the read was successful

Originally Posted by vart

the eof flag is set as a result of the failed operation.

it means - BEFORE failure it is always false.

AFTER failaure - you will chekc it on the next iteration only.

Instead you should check the return value of th eread operation - and if it fails - do not enter the loop

for istreams
if(istr >> x)

is a standard way to check that the read was successful

the compiler can only tell the TRUE or FALSE ,right?

I never know about the Falure.

why if cin>> line is in the block,also, cause the strange result?

thanks

Originally Posted by hth373737

why if cin>> line is in the block,also, cause the strange result?

thanks

Because you have read 2 lines and processed only the second one i neach iteration