Maintaining float precision string parsing

beginners
#1

Hi,

So I have a project where I’m parsing lots of floats from a csv with the great ofxCsv addon.

Once I have my numbers as std::string, ex: “-706482,4243618”, the floats are formatted with a comma separator.

I have a simple function that replaces the comma with a dot. i.e.,

float formatNum(const string & s){
	float ret = -1;
	size_t pos = s.find(",");
	if(pos == s.npos){ cout << "no dot formatNum"; return ret; }

	string numstr = s;
	numstr.replace(pos, 1, ".");

	return ofToFloat(numstr);
}

The number this function outputs is something like -70648.4243

Do you have an idea to get the full number on the string instead of this truncated working example?

Thanks

#2

i’d try ofToDouble instead

#3

thanks & just tried, but I’m getting exactly equivalent results with float or double data types

perhaps using python to do the parsing?

for this example i can live with this precision loss (gps coords), would be nice to know if someone already dove into big numbers and keeping exact precison under c++. yeah, i’m aware of mantissa and exponents float/double precision. perhaps boost bignumbers?

cheers

#4

have you changed the type of the return value of the function? if you use ofToDouble but then return float you’ll loose precision again

#5

of course I have changed :slight_smile:

	// float 				latitude;
	// float 				longitude;
	// float 				height;
	double 				latitude;
	double 				longitude;
	double 				height;


	double formatNum(const string & s){
		float ret = -1;
		size_t pos = s.find(",");
		if(pos == s.npos){ ofLog() << "no dot formatNum"; return ret; }

		string numstr = s;
		numstr.replace(pos, 1, ".");

		// return 0.0f;
		return ofToDouble(numstr);

	}
#6

It seems this is just a problem of how c++ outputs floats/doubles by default, the number you are getting should be correct, is only when showing it in the console that appears with less precision.

try:

std::cout << std::setprecision(15) << ofToFloat(numstr) << std::endl;

should work as well with ofLog

#7

You are right, now the full number get logged in the console.

Thanks