pointer to a constant string - C / C++ / MFC Discussion Boards

Re: Pointers, Functions and XCode messages

jschell8-Jun-14 9:12

jschell

8-Jun-14 9:12

ericgahn wrote:
Sphere s;

That line of code is creating the instance on the stack. The stack is only valid within the method and there is no assurance that it will continue to be valid.

You need to allocate it on the heap - look at the malloc method and associated other methods.

And remember to delete it when you are done with it.

Re: Pointers, Functions and XCode messages

ericgahn8-Jun-14 10:01

ericgahn

8-Jun-14 10:01

Thank you for your reply.

Very helpful. I googled malloc() and used this site to further understand suggested soln.

Eric

Re: Pointers, Functions and XCode messages

CPallini8-Jun-14 10:00

CPallini

8-Jun-14 10:00

As another option, you could change your function this way

void MakeSphere(float *centre, float *radius, Sphere *);

and initialize the struct allocated by the caller.

Veni, vidi, vici.

Re: Pointers, Functions and XCode messages

ericgahn8-Jun-14 10:05

ericgahn

8-Jun-14 10:05

CPallini wrote:
void MakeSphere(float *centre, float *radius, Sphere *);

So if I understand correctly a Sphere 'instance' would be created in Main() and then a pointer to this instance passed to the function?

Re: Pointers, Functions and XCode messages

CPallini8-Jun-14 10:11

CPallini

8-Jun-14 10:11

Yes, you got it right.

Veni, vidi, vici.

how can use a non-static class member function as the custom deleter of std::unique_ptr?

Falconapollo7-Jun-14 21:18

Falconapollo

7-Jun-14 21:18

When I attempt to set custom deleter of std::unique_ptr, I got this error:
.\src\iMoney.cpp(5): error C2664: 'std::unique_ptr<_Ty,_Dx>::unique_ptr(HINSTANCE__ *,void (__cdecl *const &)(HMODULE))' : cannot convert parameter 2 from 'void (__thiscall iMoney::* )(HMODULE)' to 'void (__cdecl *const &)(HMODULE)'
2> with
2> [
2> _Ty=HMODULE,
2> _Dx=void (__cdecl *)(HMODULE)
2> ]
2> Reason: cannot convert from 'void (__thiscall iMoney::* )(HMODULE)' to 'void (__cdecl *const )(HMODULE)'
2> There is no context in which this conversion is possible
2>
2>Build FAILED.

anybody can help me?

Here is my code snippet:

C++

//this is my non-static class member variable
std::unique_ptr<HMODULE, decltype(&iMoney::freeLib)>			m_ptrModule;

void iMoney::freeLib(HMODULE hModule)//this is the non-static class member function
{
	m_pThisApp->FreeLibrary(hModule);
}

//this my constructor
iMoney::iMoney(CReader_App* pApp)
: m_pThisApp(pApp)
, m_ptrModule(nullptr, &iMoney::freeLib)
{
//hello money, i love you so much~
}

Re: how can use a non-static class member function as the custom deleter of std::unique_ptr?

jschell8-Jun-14 9:17

jschell

8-Jun-14 9:17

I believe the delete method should take a iMoney not HMODULE (which is what the error says.) And since it takes an iMoney there is no reason for it to not be static.

pointer to a constant string

bkelly137-Jun-14 12:51

bkelly13

7-Jun-14 12:51

Windows 7, visual Studio 2008, C++

 WCHAR *op_type = NULL;
if( x )
   op_type = &L"First";
else
   op_type = &L"Second";

This solicits the error

Quote:
error C2440: '=' : cannot convert from 'const wchar_t (*)[6]' to 'WCHAR *'

What is my syntax error?

I tried the declaration:

const wchar_t *op_type2 = NULL;

and received the error:

Quote:
error C2440: '=' : cannot convert from 'const wchar_t (*)[6]' to 'const wchar_t *'

Which seems wrong to me. Why does the pointer care how long the string is? It is but the address of the first character.

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

modified 7-Jun-14 20:28pm.

Re: pointer to a constant string

«_Superman_»7-Jun-14 21:59

«_Superman_»

7-Jun-14 21:59

For the first part of your question, you do not need the & sign.

WCHAR *op_type = NULL;
if( x )
   op_type = L"First";
else
   op_type = L"Second";

For the second part of your question, you should not be getting any errors.
It is a valid statement.

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++) (October 2009 - September 2013)

Polymorphism in C

Re: pointer to a constant string

bkelly138-Jun-14 5:00

bkelly13

8-Jun-14 5:00

Lets see if I really understand what you told me.
The declaration:

const WCHAR *op_type = NULL;

was good. The use:

op_type = &L"Shutdown";

was incorrect. The declaration of the constant string:

&L"Shutdown";

is effectively a WCHAR array. Arrays are always passed by address so adding the & symbol was creating an pointer to a pointer. The error message:

Quote:
error C2440: '=' : cannot convert from 'const wchar_t (*)[9]' to 'const WCHAR *'

was telling me that but I was too wrapped up in reading the [9] as a length rather than an indicator that this is an array and the address is passed rather than the value.

Thank you for helping me with this.

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

Re: pointer to a constant string

leon de boer8-Jun-14 7:50

leon de boer

8-Jun-14 7:50

You logic is flawed but your result is correct.

The "L" prefix is a sort of precompiler literal Microsoft has put in place it's not a macro or such and it is sort of bound like the quotes are in the precompiler

look at how you write a normal string constants

const char* txtcnst = "SOME_CONSTANT_TEXT";

There is no "&" pointer there so why just because you want a unicode string would they change it

The answer is it is the way it is because that is how C language defined the use of constants and think of L as part of the quotes "" simply telling the compiler the text is unicode format.

In vino veritas

Re: pointer to a constant string

CPallini8-Jun-14 10:04

CPallini

8-Jun-14 10:04

As far as I know L is not a Microsoft thing, see, for instance "string literal" at cppreference.com[^].

Veni, vidi, vici.

Is this Code Valid?

Manikandan106-Jun-14 17:42

Manikandan10

6-Jun-14 17:42

Is this line of code valid in C++:

C++

int a{1};

Re: Is this Code Valid?

Shao Voon Wong6-Jun-14 18:45

Shao Voon Wong

6-Jun-14 18:45

Valid in C++11

Re: Is this Code Valid?

Manikandan106-Jun-14 18:54

Manikandan10

6-Jun-14 18:54

Thanks for your reply.

what does it do

bkelly137-Jun-14 14:33

bkelly13

7-Jun-14 14:33

My searches revealed only a partial answer to int a{1};

What does this do and why might I use it?

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

Re: what does it do

Richard MacCutchan7-Jun-14 22:34

Richard MacCutchan

7-Jun-14 22:34

It merely initialises the variable to the value in braces.

C++

int i = 1; // and
int i{1};
// are the same

See http://msdn.microsoft.com/en-us/library/w7wd1177.aspx[^].

Re: what does it do

bkelly138-Jun-14 4:52

bkelly13

8-Jun-14 4:52

I should have included "initialize" in my search.
On one hand it really doesn't add anything.
On the other, it can standardize initialization methods. An int can be initialized in the same manner as an array. That is of little significance, but often consistency adds more than is immediately apparent.

Thanks for taking the time to reply.

Thank you for your time
If you work with telemetry, please check this bulletin board: www.irigbb.com

Re: Is this Code Valid?

Randor 6-Jun-14 23:43

Randor

6-Jun-14 23:43

Hi,

Yes. This is the new direct list initialization available in C++11.

Best Wishes,
-David Delaune

Re: Is this Code Valid?

Manikandan107-Jun-14 0:00

Manikandan10

7-Jun-14 0:00

Thank you for your reply.

about speex and ogg！

renxiaoyaoa85-Jun-14 21:08

renxiaoyaoa8

5-Jun-14 21:08

Friends, how to compress speex ogg packets into a *. Oog file?(can make music player play the files)
please！

WiX Toolset Compiler error

sreehari_mysore5-Jun-14 19:26

sreehari_mysore

5-Jun-14 19:26

I am getting the errors related to WiX Toolset while compiling one of the applications of C++ in VS2005.

The error message shows that:

"WiX Toolset compiler has encountered a problem and needs to close".

I googled for the related information and tried by installing the 2007 version of Toolset compiler wix38.exe. But still not able to resolve the issue.

Please let me know how to rectify the error..

Re: WiX Toolset Compiler error

Richard MacCutchan5-Jun-14 22:08

Richard MacCutchan

5-Jun-14 22:08

Without any more detail no one can guess what is wrong. You would be better posting your query on a forum dedicated to this product, since it has nothing to do with C++ per se.

Made of libogg ogg files can be directly through the player play?

renxiaoyaoa85-Jun-14 16:10

renxiaoyaoa8

5-Jun-14 16:10

Why the generated *. Ogg cannot play?

Re: Made of libogg ogg files can be directly through the player play?

Richard MacCutchan5-Jun-14 22:05

Richard MacCutchan

5-Jun-14 22:05

Please read http://www.codeproject.com/Messages/2922875/HOW-TO-ASK-A-QUESTION.aspx[^] again, and see http://www.codeproject.com/Messages/4834174/Re-How-to-use-MFC-speex-audio-files-WAV-format-for.aspx[^].

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