File I/O

**mikeman** · 03-05-2010

I'm trying to read in a file which is formatted like so:

Char_Array Int
Char_Array Int
.
.
.

There is a single space in between the array and the int. How can I read in from this, and store them into proper variable (type char and int) to be manipulated by a function? They may be single or multiple digit integers.

My thought is to use something like get, and store whatever is retrieved into the char array until the ' ' is met, and store the rest into the int until '\n', but not really sure how to achieve this.

**MK27** · 03-05-2010

Okay, so you mean this is a text file like this:

Code:

some_string 7
etc 666

I'm asking because you can store arrays, ints and other datatypes directly into a "binary" non-text file.

If it is text, you can use ifstream::getline(), then apply sscanf():

Code:

char input[64]; // filled with getline
char string[32];
int x;
sscanf(input, "%[^ ] %d", string, &x);

Note this invloves C strings, not a C++ strings. %[^ ] reads all characters up to (but not including) a space.

**mikeman** · 03-05-2010

Yes, it is a text file.

Specifically, it has a Name, then an ID.

John 123
James 456
Joel 135

**mikeman** · 03-05-2010

How can I implement this using C++ syntax, instead of C?

**laserlight** · 03-05-2010

Originally Posted by mikeman

How can I implement this using C++ syntax, instead of C?

As in use functionality available via <fstream>? Before any answer is suggested, I would like to know if the name field can contain whitespace. If so, what separates the name field from the id field?

Furthermore, suppose that the file's contents was:

Code:

John 123 James 456 Joel 135

Would you like to report an error, or would you be fine with accepting this otherwise incorrect format?

**mikeman** · 03-05-2010

The name field should not contain whitespace. The whitespace should be a delimiting character. Which I've sort of tried to implement using get, but haven't been very successful.

As far as the second case goes, I suppose that would be an error. I'm doing this for a specific file, so it's not really necessary to be dynamic in that sense. After the name field is filled, I was thinking of using get again using the default '\n' delimiter. But then I'm not sure how to turn this from a char array into an int.

**laserlight** · 03-05-2010

Okay, here's an idea: use std::getline() to read each line into a std::string object. Initialise a std::stringstream object using this std::string. Now, use formatted input with operator>> to read from this stringstream into a std::string (name) and an int (id), possibly ignoring trailing whitespace with the std::ws input stream manipulator. If the read failed or if eof() was not reached on the stringstream, report an input error. Otherwise, do as you will with the name and id, then go on to read the next line.

**mikeman** · 03-05-2010

I'm not following too well.

I get the first part to use getline.

Code:

getline(infile, temp)

But I'm not too sure what you're meaning from here.

**laserlight** · 03-05-2010

Something like this:

Code:

std::string line;
while (std::getline(infile, line))
{
    std::string name;
    int id;
    std::stringstream ss(line);
    if ((ss >> name >> id >> std::ws) && ss.eof())
    {
        // Use name and id.
    }
    else
    {
        // Handle incorrect line format.
    }
}

**mikeman** · 03-05-2010

Ok, in the file, % precedes a command, say insert, end, print, etc, to be done on a linked list.

Here is what I did, but it's not working. Builds fine, but has error that doesn't allow it to run (force closes), not like endless loop. I simplified the file being read to get this working and at the moment it's just:

Code:

%INSERT
MARK 129
DAVID 205
JOHN 440
%PRINT

So, when operational, it adds MARK, DAVID, and JOHN to the linked list with their respective ID.

Code:

if (strcmp(Next, "%INSERT")==0) {
	while (infile.peek() != '%') {
		getline(infile, line); 
		stringstream ss(line);
		if ((ss >> name1 >> ID >> ws) && ss.eof()) {
			strcpy_s(Name, name1.c_str());
			list.add_entry(Name, ID);
		}//if
	}//while
}//if

**mikeman** · 03-05-2010

Nevermind, the error is happening elsewhere.

Thanks for the help!

**mikeman** · 03-05-2010

.
..

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