C++ String to Double Conversion

Converting string to double in C#

There are 3 problems.

1) Incorrect decimal separator

Different cultures use different decimal separators (namely , and .).

If you replace . with , it should work as expected:

Console.WriteLine(Convert.ToDouble("52,8725945"));

You can parse your doubles using overloaded method which takes culture as a second parameter. In this case you can use InvariantCulture (What is the invariant culture) e.g. using double.Parse:

double.Parse("52.8725945", System.Globalization.CultureInfo.InvariantCulture);

You should also take a look at double.TryParse, you can use it with many options and it is especially useful to check wheter or not your string is a valid double.

2) You have an incorrect double

One of your values is incorrect, because it contains two dots:

15.5859949000000662452.23862099999999

3) Your array has an empty value at the end, which is an incorrect double

You can use overloaded Split which removes empty values:

string[] someArray = a.Split(new char[] { '#' }, StringSplitOptions.RemoveEmptyEntries);


How do I convert a CString to a double in C++?

A CString can convert to an LPCTSTR, which is basically a const char* (const wchar_t* in Unicode builds).

Knowing this, you can use atof():

CString thestring("13.37");
double d = atof(thestring).

...or for Unicode builds, _wtof():

CString thestring(L"13.37");
double d = _wtof(thestring).

...or to support both Unicode and non-Unicode builds...

CString thestring(_T("13.37"));
double d = _tstof(thestring).

(_tstof() is a macro that expands to either atof() or _wtof() based on whether or not _UNICODE is defined)

C++ string to double conversion

You can convert char to int and viceversa easily because for the machine an int and a char are the same, 8 bits, the only difference comes when they have to be shown in screen, if the number is 65 and is saved as a char, then it will show 'A', if it's saved as a int it will show 65.

With other types things change, because they are stored differently in memory. There's standard function in C that allows you to convert from string to double easily, it's atof. (You need to include stdlib.h)

#include <stdlib.h>

int main()
{
    string word;  
    openfile >> word;
    double lol = atof(word.c_str()); /*c_str is needed to convert string to const char*
                                     previously (the function requires it)*/
    return 0;
}

Convert double/float to string

The only exact solution is to perform arbitrary-precision decimal arithmetic for the base conversion, since the exact value can be very long - for 80-bit long double, up to about 10000 decimal places. Fortunately it's "only" up to about 700 places or so for IEEE double.

Rather than working with individual decimal digits, it's helpful to instead work base-1-billion (the highest power of 10 that fits in a 32-bit integer) and then convert these "base-1-billion digits" to 9 decimal digits each at the end of your computation.

I have a very dense (rather hard to read) but efficient implementation here, under LGPL MIT license:

http://git.musl-libc.org/cgit/musl/blob/src/stdio/vfprintf.c?h=v1.1.6

If you strip out all the hex float support, infinity/nan support, %g/%f/%e variation support, rounding (which will never be needed if you only want exact answers), and other things you might not need, the remaining code is rather simple.

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