How to convert wchar_t* to long c++

Question

As the title indicates I need to know the best way to convert wchar_t* to long in visual c++. Is it possible to do that? If possible how to do that?

What do you mean by "covert"? Can you please exit your question to include example input and output? And what have you tried yourself? — Some programmer dude, Aug 14 '15 at 09:34
Your question is unclear. At first I thought that you want to convert the `wchar_t` pointer to `long`, which is not "possible" on 64-bit Windows. Only after reading the answer I know that you want to convert the character string stored in `wchar_t*` to `long` — phuclv, Aug 14 '15 at 10:48

score 6 · Accepted Answer · answered Aug 14 '15 at 09:32

6

Use _wtol() to Convert a wide-character string to a long.

wchar_t *str = L"123";
long lng = _wtol(str);

answered Aug 14 '15 at 09:32

Deadlock

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`_wtol`? Really? Is that really the best way in C++? Is that even a C++ function or is it an MS specific function? Why do you link to CE docs. How are errors handled? Is it the case that `_wtol(L"foo") == _wtol(L"0")`? – David Heffernan Aug 14 '15 at 09:35
if you have a better way to do that you can mention here. :) – Deadlock Aug 14 '15 at 09:55
1

That's a rather weak response – David Heffernan Aug 14 '15 at 10:05
The lack of error reporting is a restriction that needs to be spelled out. If an application doesn't need error reporting here, then this may be a viable solution. For all other instances, [the other answer](http://stackoverflow.com/a/32007302/1889329) is superior, and should really be the accepted answer. – IInspectable Aug 14 '15 at 11:16
@IInspectable I wouldn't say my answer is necessarily superior as `_wtol` seems to run much faster. A quick profile on my machine showed that it runs in ~40ns versus ~100ns for the other methods. – sjdowling Aug 14 '15 at 15:18
@sjdowling: It all depends on the specific needs, of course. Inability to identify failures, however, is generally undesirable. I did point out, that your answer is superior, **if** error reporting is required. I suppose, we can agree on that part. – IInspectable Aug 14 '15 at 15:36

sjdowling · Answer 2 · 2015-08-14T16:03:57.960

Use boost::lexical_cast.

#include <iostream>
#include <boost/lexical_cast.hpp>

int main()
{
    const wchar_t* s1 = L"124";
    long num = boost::lexical_cast<long>(s1);
    std::cout << num;
    try
    {
        const wchar_t* s2 = L"not a number";
        long num2 = boost::lexical_cast<long>(s2);
        std::cout << num2 << "\n";
    }
    catch (const boost::bad_lexical_cast& e)
    {
        std::cout << e.what();
    }
}

Live demo

Use std::stol.

#include <iostream>
#include <string>

int main()
{
    const wchar_t* s1 = L"45";
    const wchar_t* s2 = L"not a long";

    long long1 = std::stol(s1);
    std::cout << long1 << "\n";
    try
    {
        long long2 = std::stol(s2);
        std::cout << long2;
    }
    catch(const std::invalid_argument& e)
    {
        std::cout << e.what();
    }    
}

Live Demo.

Use std::wcstol

#include <iostream>
#include <cwchar>

int main()
{
    const wchar_t* s1  = L"123";
    wchar_t *end;
    long long1 = std::wcstol(s1, &end, 10);
    if (s1 != end && errno != ERANGE)
    {
        std::cout << long1;
    }
    else
    {
        std::cout << "Error";
    }
    const wchar_t* s2  = L"not a number";
    long long2 = std::wcstol(s2, &end, 10);
    if (s2 != end && errno != ERANGE)
    {
        std::cout << long2;
    }
    else
    {
        std::cout << "Error";
    }
}

Live Demo

I ran some benchmarks with 100 samples of each of these methods as well as _wtol converting the string L"123".

[std::stol](http://en.cppreference.com/w/cpp/string/basic_string/stol) requires C++11. A solution based on [stringstream](http://en.cppreference.com/w/cpp/io/basic_stringstream)s can be used with pre-C++11 as well. This, too, can be implemented to report errors. — IInspectable, Aug 14 '15 at 10:32
@IInspectable You can achieve this with stringstreams but I would consider them to be a last resort given how [horrifically slow](http://tinodidriksen.com/2010/02/07/cpp-convert-int-to-string-speed/) they [can be](http://www.boost.org/doc/libs/1_59_0/doc/html/boost_lexical_cast/performance.html). — sjdowling, Aug 14 '15 at 10:47
Performance may not be everyone's primary goal, and *"horrifically slow"* may still be fast enough. Taking a dependency on boost may not be feasible in every scenario, and C++11 may not be available. Since SO is about general applicability, offering options alongside a rationale is usually a good idea. — IInspectable, Aug 14 '15 at 10:52

How to convert wchar_t* to long c++

2 Answers2