(C++) std::istringstream reads up to 6 digits from string to double

Question

folks! I've been struggling with this problem for some time and so far I haven't found any solution to it.

In the code below I initialize a string with a number. Then I use std::istringstream to load the test string content into a double. Then I cout both variables.

#include <string>
#include <sstream>
#include <iostream>

std::istringstream instr;

void main()
{
    using std::cout;
    using std::endl;
    using std::string;

    string test = "888.4834966";
    instr.str(test);

    double number;
    instr >> number;

    cout << "String test:\t" << test << endl;
    cout << "Double number:\t" << number << endl << endl;
    system("pause");
}

When I run .exe it looks like this:

String test: 888.4834966
Double number 888.483
Press any key to continue . . .

The string has more digits and it looks like std::istringstream loaded only 6 of 10. How can I load all the string into the double variable?

try `instr.precision(8)` before `instr.str(test);` – Alexandru Barbarosie Jul 10 '13 at 20:27 — Alexandru Barbarosie, Jul 10 '13 at 20:27

score 5 · Answer 1 · answered Jul 10 '13 at 20:29

#include <string>
#include <sstream>
#include <iostream>
#include <iomanip>

std::istringstream instr;

int main()
{
    using std::cout;
    using std::endl;
    using std::string;

    string test = "888.4834966";
    instr.str(test);

    double number;
    instr >> number;

    cout << "String test:\t" << test << endl;
    cout << "Double number:\t" << std::setprecision(12) << number << endl << endl;
    system("pause");

    return 0;
}

It reads all of the digits, they're just not all displayed. You can use std::setprecision (found in iomanip) to correct this. Also note that void main is not standard you should use int main (and return 0 from it).

sedavidw · Answer 2 · 2013-07-11T14:04:31.677

1

The precision of your output probably just isn't showing all of the data in number. See this link for how to format your output precision.

edited Jul 11 '13 at 14:04

answered Jul 10 '13 at 20:29

sedavidw

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Standard input methods don't use `precision()`. – aschepler Jul 10 '13 at 20:37

score 1 · Answer 3 · answered Jul 10 '13 at 20:59

Your double value is 888.4834966 but when you use:

cout << "Double number:\t" << number << endl << endl;

It uses a default precision for double, to set it manually use:

cout << "Double number:\t" << std::setprecision(10) << number << endl << endl;

(C++) std::istringstream reads up to 6 digits from string to double

3 Answers3