writing ascii to a file

Hi,

i'm currently working on a knn classificator and want to save the classifed probe as an ascii file (so i can edit it manually for missclassified tfingertip).
This is my struct:

Code:

typedef struct{
  int x;
  int y;
  int c;
} tfingertip;

i want to write each tfingertip as one row seperated by ;
so it looks like:
15;30;1;
44;26;3;

then i want to read it out rowwise so i can math the distance to each list element (putting the values in the list isnt the problem, the problem is the file writing/reading)

i would also like to name the filename by timestamp so while automated learning (if turned on) i can select which file to take if the knn begin to fail with misclassified tfingertips.

edit: i would also like to sort the rows by its c (fingerclass) so its easier to read for manual editing.


Thanks in advance!

~Jan

To put a timestamp in the filename, use the _strdate()/_strtime() functions, and sprintf() them to a var.
To read/write from/to files, use fread()/fprintf()

is that C ? i want to do it in C++ with streams if possible

>>is that C ? i want to do it in C++ with streams if possible
Writing to stream

Code:

#include <fstream>
#include <list>

using namespace std;

struct fingertip {
	int x;
	int y;
	int c;
};

ostream& operator<<(ostream& os,const fingertip& ft)
{
	os << ft.x << ';' << ft.y << ';' << ft.c << '\n';
	return os;
}

...
ofstream fileOut("ft.txt");
list<fingertip> lft;
fingertip tf = {1,2,3};
lft.push_back(tf);
lft.push_back(tf);
typedef list<fingertip>::const_iterator ftiter;
	for(ftiter i = lft.begin();i != lft.end();++i)
		fileOut << *i;

For reading implement the istream operator>> .

Code:

istream& operator>>(istream& is,fingertip& ft)
...

the istream is the problem i have. I don't know how to divide the string x;y;c so i have again ft.x ft.y ft.c

Thanks in advance!

~Jan

the code should look something like this

Code:

ofstream cFile("name of file.txt");

cFile<<string<<"\n";  // \n is a return

Not the most eloquent code, but it ought to work:

Code:

fingertip& operator>>(istream& is, fingertip& ft)
{
	string line;
	int first, last;
	getline(is, line);
	first = line.find_first_of(';');
	last = line.find_last_of(';');
	ft.x = atoi(line.substr(0, first).c_str());
	ft.y = atoi(line.substr(first + 1, last - (first + 1)).c_str());
	ft.c = atoi(line.substr(last + 1, line.size() - (last + 1)).c_str());
	cout << ft.x << endl;
	cout << ft.y << endl;
	cout << ft.c << endl;
	return ft;
}

Works for input like 1;2;3

Code:

istream& operator>>(istream& is,fingertip& ft)
{
	fingertip tempft;
	char c = 0;
	if(is.fail())
		return is;
	is >> tempft.x >> c;
	if(is.fail() || c != ';')
		throw invalid_argument("Error description...");
	is >> tempft.y >> c;
	if(is.fail() || c != ';')
		throw invalid_argument("Error description...");
	is >> tempft.c;
	if(is.fail())
		throw invalid_argument("Error description...");
	ft = tempft;
	return is;
}

this is giving me a headache:

Code:

int count(char filen) {

ifstream filena(filen);

while (filena.getline( line, 6))
{
num++;
};
return num;
}

Compiler:
knnprobe.cc: In function `int count(char)':
knnprobe.cc:145: error: invalid conversion from `char' to `const char*'
knnprobe.cc:145: error: initializing argument 1 of `
std::basic_ifstream<_CharT, _Traits>::basic_ifstream(const char*,
std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits<char>]'
knnprobe.cc:297:2: warning: no newline at end of file


thanks in advance!

~Jan

The ifstream constructor requires a char pointer, not a char. So does the getline function in ifstream.

Code:

int count(string filen) {

ifstream filena(filen.c_str());

while (getline(filena, line, 6))
{
num++;
} //; not nescessary
return num;
}