[c++]ifstream, stuck in loop... - Tilted Forum Project Discussion Community

j0hnb · 11-23-2004, 02:34 AM

I'm using ifstream to scan in integers from a file, but I come into a problem when there is a character mixed up within the integer list. It will read correctly till it hits the character then loop forever on the integer before. The inFile position woun't move up. How do I fix this problem? This is my code from that section that I am having a problem with.

Code:

ifstream inFile; 
         
inFile.open(fname);

if (!inFile)
        {
        return 0;
        }
         

while (!inFile.eof())
        {
        inFile >> x
        if(isdigit(x))
                {
                tmp[i] = x;
                i++;
                }

Silvy · 11-23-2004, 02:45 AM

So tmp[] is filled with exactly what you'd expect, until that 'erroneous' character?

j0hnb · 11-23-2004, 02:50 AM

yep. The file it reads is something like this
10 -3 25 15 8 25 6 oops!
it will read correctly hit the 6 and then loop the 6 forever... I have to force it out of the loop, otherwise it would stay in there forever. For some reason I can't get it to give me anything that i could use as a key to force it out. Any ideas?

Silvy · 11-23-2004, 02:56 AM

Are you doing anything else in that while-loop? 'cause I can't see anything that would break the loop (with very limited c++ knowledge I might add)

edit: perhaps it's the variable type of 'x' that is causing the problem?
will the '>>' operator fail with an incorrect variable? (i.e. if x is declared as an int, will assigning a string fail, thus not moving the filepointer towards EOF, and retaining the original value of 'x'?)

j0hnb · 11-23-2004, 11:20 AM

I'm not doing anything else in the while loop, it is set to end at EOF but if it works correctly it should keep moving down the file and once it finish's reading in the characters it should quit, and I would be able to set it to ignore the character and just read the int's. But the way it is working is when it hits the char it goes back a place to the last int in the list... That is where my problem lies. I tried taking it in as characters and then i was stuck with single characters not the full numbers. I could set it with a getline to stop on a space... Then cast it as an int and save it to an int... But that is the only way of fixing it that I can think of right now. Any ideas?

Pragma · 11-23-2004, 06:55 PM

So the way I read it, your problem is that you're expecting someone to input a string containing nothing but numbers. If the string contains other symbols, things start messing up.

This is pretty much predicable (and expected) behaviour. The problem you're running into is that when you pass the >> operator an Integer variable, if it doesn't have an integer, it won't move past that spot in the input stream. This is so that another >> operator can read the value into another type of variable.

A better idea would be to read the entire line into a string, then use some kind of string tokenizer or regular expression to break it apart by spaces. Then, you can read each value into your array if it's an integer - if not, ignore it and continue.

j0hnb · 11-23-2004, 06:57 PM

yea, that's the solution i came down to, i'm currently rewriting it as a string, then turning that into an int for the rest of the program. Thanks

11-23-2004, 02:34 AM	#1 (permalink)
j0hnb Crazy Location: Arnold, MD	[c++]ifstream, stuck in loop... I'm using ifstream to scan in integers from a file, but I come into a problem when there is a character mixed up within the integer list. It will read correctly till it hits the character then loop forever on the integer before. The inFile position woun't move up. How do I fix this problem? This is my code from that section that I am having a problem with. Code: ifstream inFile; inFile.open(fname); if (!inFile) { return 0; } while (!inFile.eof()) { inFile >> x if(isdigit(x)) { tmp[i] = x; i++; }

11-23-2004, 02:45 AM	#2 (permalink)
Silvy paranoid Location: The Netherlands	So tmp[] is filled with exactly what you'd expect, until that 'erroneous' character? __________________ "Do not kill. Do not rape. Do not steal. These are principles which every man of every faith can embrace. " - Murphy MacManus (Boondock Saints)

11-23-2004, 02:56 AM	#4 (permalink)
Silvy paranoid Location: The Netherlands	Are you doing anything else in that while-loop? 'cause I can't see anything that would break the loop (with very limited c++ knowledge I might add) edit: perhaps it's the variable type of 'x' that is causing the problem? will the '>>' operator fail with an incorrect variable? (i.e. if x is declared as an int, will assigning a string fail, thus not moving the filepointer towards EOF, and retaining the original value of 'x'?) __________________ "Do not kill. Do not rape. Do not steal. These are principles which every man of every faith can embrace. " - Murphy MacManus (Boondock Saints) Last edited by Silvy; 11-23-2004 at 02:59 AM..

11-23-2004, 02:50 AM	#3 (permalink)
j0hnb Crazy Location: Arnold, MD	yep. The file it reads is something like this 10 -3 25 15 8 25 6 oops! it will read correctly hit the 6 and then loop the 6 forever... I have to force it out of the loop, otherwise it would stay in there forever. For some reason I can't get it to give me anything that i could use as a key to force it out. Any ideas?

11-23-2004, 11:20 AM	#5 (permalink)
j0hnb Crazy Location: Arnold, MD	I'm not doing anything else in the while loop, it is set to end at EOF but if it works correctly it should keep moving down the file and once it finish's reading in the characters it should quit, and I would be able to set it to ignore the character and just read the int's. But the way it is working is when it hits the char it goes back a place to the last int in the list... That is where my problem lies. I tried taking it in as characters and then i was stuck with single characters not the full numbers. I could set it with a getline to stop on a space... Then cast it as an int and save it to an int... But that is the only way of fixing it that I can think of right now. Any ideas?

11-23-2004, 06:55 PM	#6 (permalink)
Pragma I am Winter Born Location: Alexandria, VA	So the way I read it, your problem is that you're expecting someone to input a string containing nothing but numbers. If the string contains other symbols, things start messing up. This is pretty much predicable (and expected) behaviour. The problem you're running into is that when you pass the >> operator an Integer variable, if it doesn't have an integer, it won't move past that spot in the input stream. This is so that another >> operator can read the value into another type of variable. A better idea would be to read the entire line into a string, then use some kind of string tokenizer or regular expression to break it apart by spaces. Then, you can read each value into your array if it's an integer - if not, ignore it and continue.

11-23-2004, 06:57 PM	#7 (permalink)
j0hnb Crazy Location: Arnold, MD	yea, that's the solution i came down to, i'm currently rewriting it as a string, then turning that into an int for the rest of the program. Thanks