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

Question

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

Unicode support would be nice also.

Thanks!

Solution 1

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)

Solution 2

You can convert anything to anything using a std::stringstream. The only requirement is that the operators >> and << be implemented. Stringstreams can be found in the <sstream> header file.

std::stringstream converter;
converter << myString;
converter >> myDouble;

Solution 3

with the boost lexical_cast library, you do

#include <boost/lexical_cast.hpp>
using namespace boost;

...

double d = lexical_cast<double>(thestring);

Solution 4

strtod (or wcstod) will convert strings to a double-precision value.

(Requires <stdlib.h> or <wchar.h>)

View more solutions

Comments

[Steve Duitsman]

This link shows you "wcstod" which is what I used to support unicode. msdn.microsoft.com/en-us/library/kxsfc1ab(VS.80).aspx

[Dave Hillier]

Consider some more context to the page you're adding

[Pete]

This works, but IMO MighMoS's suggestion of std::stringstream is a bit cleaner.

[Shog9]

Usage examples wouldn't go amiss either... See the accepted answer.

[Rolf Kristensen]

_wcstod_l / _tcstod_l allows one to specify locale, so one can handle localized format (decimal delimiter as comma or dot etc.)

[Philm]

This sounded good to me. Unfortunately it didn't work for the questioned scenario here with the Microsoft (MFC) CString type. I got this compiled, but the converted double number seemed to be random, at least it had no relation to the string. I hope, it works good for other types which implement the << and >> Operators better. I am no expert yet in using the std strings in C++, but to me a converter which results in wrong numbers without throwing an error or exception is very dangerous.

[Philm]

Remark: The other Suggestion here, _tstof() worked fine for converting a CString to a double for me.

[IInspectable]

@Philm: This answer can be used with MFC's CString objects just fine. You don't need an operator<<() either. That's what the constructor is for: std::wstringstream converter(myString);. Note that this requires a CStringW (which, in the majority of cases, is the correct type anyway). However, there's still a silent killer in there. It seems to be clear, elegant. And wrong. It uses the current thread locale for the conversion. This may or may not be what you want. Better to use a solution that allows you to explicitly specify the locale to use for the conversion.