Converting string to double, but extra numbers are added

[daven25]

Hi, I'm trying to convert a string to a double. The string should be in this format: "0.04". However, when I convert from a string to a double using atof, the new double's value is "0.0400000000001". How do I get it to just convert two the two decimal place without adding all of the extra numbers at the end?

#include <iostream>
using namespace std;
#include <string>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <ctype.h>

double getPrice(string test)
{
//(test = "0.04")
double price = atof(test.c_str());
return price;
}

input: "0.04"
expected output: 0.04
actual output: 0.040000000001

[georgewashere]

cout.precision(number);

more reading : http://www.cplusplus.com/reference/iostream/ios_base/precision/

[daven25]

Thanks george but that only works if you're going to push it to 'cout' right? What if I'm returning as part of a my member function?

[daven25]

I should also add that the string is passed as a parameter and will not always be the same length.

[Texan40]

just another possibility without using atof():

#include <iostream>
#include <sstream>

const char *amt = "1.04";

int main()
{
  std::stringstream ss(amt);
  float f = 0.0;
  ss >> f;
  std::cout << f << std::endl;
  return 0;
}

[daven25]

Thanks Texan, but I'm trying to return it as a value, not push it to the cout operator.

[Volatile Pulse]

I might be mistaken here, but I believe you're getting that one all the way at the end bc of the string being terminated. I personally don't know of a way to predict the end of the string. But have you tried casting the string to a float? I personally only use strings for letters and words. If a number is put in, I use number data types. Maybe look up what the terminating character is first, remove it from the end of the string and convert?

[daven25]

Volatile Pulse,

The program that I'm writing reads from a csv file using fstream and getline. I've created an algorithm that extracts the prices from the getline string into another string using substr.

int main()
{
	vector<test> test(100);  // Vector of objects
	int noOfTest = 0; // Number of vector objects (a counter of objects)
	importPrices(test, noOfTest); // Calls the member function importPrices
	return 0;
}

void importPrices(vector<test>& test, int& noOfTest)
{
	ifstream fin("test.csv");  // The csv file to read
	string input; // String the store the line
	while(getline(fin, input))
	{
		test[noOfTest].setPrice(getPrice(input));  // Calls the function getPrice to return a string in a double format for the object
		++noOfTest;  // Increments the counter for the objects
	}
}

double getPrice(string input)
{
	.... // Algorithm to pull the price from the string
	string test = "0.04"  // Algorithm finds the price
	double price = atof(test.c_str());
	return price;
}

I'm not sure if I can cast the string as a float in my case. Hopes this puts it into a better perspective.