Error: cannot convert from 'const char [12]' to 'const wchar_t *

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In a simple code, I have the conversion problem, and get the above error,but don't understand why! Any thoughts..

C++

CString s ="first:25.5,second,15";
if ( swscanf_s(s, "%s %f %s %d", &st1, &doub, &st2, &integ )!= 4 )

Posted 27-May-12 23:59pm

Sumal.V

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4 solutions

Solution 4

The deciding line is

if ( swscanf_s(s, L"%s %f %s %d", &st1, &doub, &st2, &integ )!= 4 )

As Nithin has written in his post, the second argument needs to be a wide character string and hence the L"... is required.

All other suggestions are more or less useless. For example, the line

CString s ="first:25.5,second,15";

it okay, because the CString knows how to convert from a char string to a wide-char string. All is ok there.

There are however a couple of other quirks in this example. First of all, if you are using swscanf_s the string arguments require an additional specifier of the buffer length. For example:

wchar_t st1 [50];
wchar_t st2 [50];
if (swscanf_s(s, L"%s %f %s %d", &st1, 50, &doub, &st2, 50, &integ )!= 4 )

Next, your input does not really match the format specifier. The %s consumes all characters up to the next white space. Hence you better change the input to:

CString s ="first 25.5 second 15";

And finally, if doub is a double variable, you should specify "%lf" as format specifier, otherwise swscanf_s assumes that you are passing the address of a float variable.

With all these changes the example will run as expected.

Posted 28-May-12 10:12am

nv3

Comments

Sumal.V 29-May-12 3:45am

Thanks for the explanation, had many doubts regarding the sscanf, swscanf functions.

Sumal.V 29-May-12 4:10am

Still have doubts on formatting a string.

char *tokenstring = "first 25.5,second 15";
result = sscanf(tokenstring, "%[^' '] %[^','],%[^' '] %s", string1, flt, string2, int1);

This is the right format for the given string, But don't understand why I must include the %[^' '] plus leave a space in between the next set of values in the string. And the last value in the string as %s! could you please give me few examples?

nv3 29-May-12 7:13am

The [abc] notation is a rather new addition to sscanf formatting. Such a pair of brackets may be used in place of the 's' format type and means that a string is read as long as it contains characters inside the brackets. If the first character in the brackets is the circumflex '^' that means that the effect is negated, i.e. scanf read a string as long as it does NOT detect a character inside the bracket. Hence you could parse your original string with the specification: "%[^:]:%lf,%[^,],%d".

The format specification that you gave in your last comment looks incorrect to me; besides it does not even contain type specifiers for the double and int variables.

You might want to take a look at the documentation of sscanf, for example on the MSDN website.

Solution 2

Try converting your code:

C++

CString s ="first:25.5,second,15";
if ( swscanf_s(s, "%s %f %s %d", &st1, &doub, &st2, &integ )!= 4 )

to:

C++

CString s =_T("first:25.5,second,15");
if ( swscanf_s(s, _T("%s %f %s %d"), &st1, &doub, &st2, &integ )!= 4 )

or

CString s =L"first:25.5,second,15";
if ( swscanf_s(s, L"%s %f %s %d", &st1, &doub, &st2, &integ )!= 4 )

By the way I think it is because of a Unicode conversion issue. The _T will help your code automatically convert from Unicode and ANSI when they are required. You can still use L"This is a sample string" instead of _T("This is a sample string").

Posted 28-May-12 1:46am

Nithin Sundar

Updated 28-May-12 1:48am

v2

Comments

Mohibur Rashid 28-May-12 9:23am

_T is supported in VC6, as far I can recall it is obsolete now, Instead TEXT is available

Solution 1

Yes it was suppose to do that.

C++

//your code:
CString s ="first:25.5,second,15";
//Change it to 
CString s =L"first:25.5,second,15";
if ( swscanf_s(s, "%s %f %s %d", &st1, &doub, &st2, &integ )!= 4 )

Posted 28-May-12 0:20am

Mohibur Rashid

Comments

Sumal.V 28-May-12 6:28am

Nope It still shows the error:
Here's my code:

int main( void )
{
int integ ;
CString st2,st1;
float doub;

CString s =L"first:25.5,second,15";

if ( swscanf_s(s, "%s %f %s %d", &st1, &doub, &st2, &integ )!= 4 )
{
cout<< "right";
}
else
cout <<"wrong";
}

stib_markc 28-May-12 6:35am

Try casting "s" with LPCTSTR; like this:
if(swscanf_s((LPCTSTR)s,....)

Sumal.V 28-May-12 6:44am

That doesn't help too...

Mohibur Rashid 28-May-12 7:43am

do you even try by yourself? did you even try to understand why I told you to add an L infront of the string? you didnt even ask what is that mean.
also change your swscanf_s function like below
swscanf_s(s, L"%s %f %s %d", &st1, &doub, &st2, &integ );

Nithin Sundar 28-May-12 7:49am

I think an explanation is needed. Please look at my answer.

Mohibur Rashid 28-May-12 9:25am

I was actually disturbed with his "That doesn't help". If op only exactly what other people says then he wont reach anywhere.

Sumal.V 28-May-12 7:59am

I know L is for LPCTSTR, unicode conversion. But the whole swscanf function is a bit of confusion for me.. Igoogled it, but did not find good examples that I can understand..

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Aescleal · Accepted Answer · 2012-05-28T01:55:00

It looks like you're mixing your character types up - swscanf_s expects wide character arguments and the version of CString you're using uses narrow characters.

If you really have to use CString and swscanf_s then make sure you've defined all the preprocessor stuff you need to make sure that CString is compiled as the wide character version. Try defining UNICODE and _UNICODE on your compiler command line.

However, as soon as you do that your declaration of the string to be parsed will all go to pot - you need to stick an L before the start of the literal string you use to initialise the string:

C++

CString s =L"first:25.5,second,15";

or use the ghastly _T macros that Microsoft introduced in about 1994:

C++

CString s = _T("Your guff in here...");

If you can't define _UNICODE or UNICODE then perhaps change the function you're using to sscanf instead - which deals with narrow arrays.

Oh, and when you do sort out the types you'll probably find it won't work the way you want it to either. But that's another problem :-)

[Your format string looks like it's for sscanf, not swscanf_s and as there's no white space between fields you're probably going to read everything into the first character buffer.]

Error: cannot convert from 'const char [12]' to 'const wchar_t *

4 solutions

Solution 3

Solution 4

Solution 2

Solution 1

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