C / C++ / MFC

char str[256] AND char *str = new char(256)

30-Jul-04 12:19

First of all, AllocSysString() returns a BSTR, which is a string type used by COM (among other things). You probably don't want this, if you're just converting string types.

If you are using MFC 7.0 or 7.1 (corresponding to VS .NET 2002 or 2003), you can do the following:

CString astring;
CStringA astring_A(astring);
const char *k = astring_A.GetBuffer();

CStringA is the char form of CString, and includes a constructor that automatically converts from the _TCHAR form (CString) if necessary. I believe that, by default, the conversion uses the CP_ACP code page.

If you are using VC6, it's a little harder:

CString astring;
int astring_A_size = (astring.GetLength() * sizeof(_TCHAR)) + 1;
char *astring_A = new char[astring_A_size];
::WideCharToMultiByte(CP_ACP,0,(LPCWSTR)astring,-1,astring_A,astring_A_size,NULL,NULL);
const char *k = astring_A;

WideCharToMultiByte is an API function that converts a wide character string to a multibyte character string according to a specified code page.

Please note that my code here is an example only. If you are using other code pages, you'll need to be more careful. Also, my allocation for astring_A in the second example is only an approximation. WideCharToMultiByte can also be used to calculate the size of the MBCS string, so that you can allocate exactly the right amount of buffer.

Software Zen: delete this;

Re: Unicode and cstring

Michael Dunn30-Jul-04 14:48

Michael Dunn

30-Jul-04 14:48

Use the ATL string conversion macro T2CA:

USES_CONVERSION;
const char* k = T2CA(LPCTSTR(astring));

--Mike--
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Re: Unicode and cstring

PJ Arends30-Jul-04 23:15

PJ Arends

30-Jul-04 23:15

instead of converting the CString to a const char * in order to use atoi or atol, use the wchar versions of the functions ( _wtoi or _wtol ). Or better yet, use the TCHAR macros, _ttoi or _ttol, in your code.

CString str = _T("123");
int num = _ttoi(str);

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"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

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Igor Mihailov30-Jul-04 10:44

Igor Mihailov

30-Jul-04 10:44

Hi, people. Can sommebody explain me the difference
between
1. char str[256]
2. char *str = new char(256)
I thought it's equevalent, but my program works good with 1st and fails sometimes when I use the second variant. Unfortunately I can't watch when it happens.

Help me

Re: char str[256] AND char *str = new char(256)

Kosk30-Jul-04 12:01

Kosk

30-Jul-04 12:01

I think what you want is:
char *str = new char [256];

[] instead of ()

Re: char str[256] AND char *str = new char(256)

Gary R. Wheeler30-Jul-04 12:24

Re: char str[256] AND char *str = new char(256)

30-Jul-04 12:24

Kosk has the correct answer, but here's a little explanation:

The first form is an array of 256 char's.

The second form returns a pointer to a single char, initialized to the value 256 (which actually initializes the value to zero, which is the lower 8 bits that fit into a single char).

What you actually want is char *str = new char[256];, which sets str to a pointer that is an array of 256 char's. Note that, with this form, when you no longer need the array, you should use delete []str.

Software Zen: delete this;

Archer28230-Jul-04 13:03

Archer282

30-Jul-04 13:03

char str[256];
is an array of characters (actually unsigned integers)

char *str = new char[256];
is a pointer to an array of characters stored in memory

this is mostly used in functions that take an output parameter.

Setting Wallpaper

Archer28230-Jul-04 10:40

Archer282

30-Jul-04 10:40

In all the examples i have come across they use SystemParameterInfo() to set the wallpaper
but apparently that just doesnt work on my OS (Win M.E.)

i know how to set it in the registry but i just need a way to update it. anyone one know how?

SPIF_SENDCHANGE ?

bikram singh31-Jul-04 16:14

bikram singh

31-Jul-04 16:14

Did you try setting the "fWinIni" parameter of SystemParametersInfo() to SPIF_SENDCHANGE ?

Bikram Singh

Initialising a items in a structure

Grahamfff30-Jul-04 10:35

30-Jul-04 10:35

I wist to initialise some items in a structure, but the only way I can see to do it is as follows:-

// General part of the Structure (used many times)<br />
typedef struct <br />
{<br />
	char	fieldDesc 	[100];<br />
	char	detailsDesc     [20];<br />
	char	unitsStr 	[10];<br />
}GENERAL_DATA;<br />
<br />
// The main structure<br />
typedef struct <br />
{<br />
	unsigned short	data; // Dyanamic data<br />
	GENERAL_DATA	details;  // Static data<br />
}ITEM_DATA;<br />
<br />
ITEM_DATA thisItem;<br />
<br />
strcpy(thisItem.details.fieldDesc,"The field description");<br />
strcpy(thisItem.details.detailsDesc,"This is the details..");<br />
etc

Are they any way I can set the char data up in ITEM_DATA, or could I set the constant data up in a new structure:-

// General Structure<br />
typedef struct <br />
{<br />
	unsigned short	data; <br />
	char	fieldDesc 	[100] = "This is a description";<br />
	char	detailsDesc     [20] = "The details....";<br />
	char	unitsStr 	[10] = "$";<br />
}ITEM_DATA_01;

etc
The above does not work, but thats what I am after!

I know what data should go into the char fields in advance, but the only way I can see to load this constant data in is via a statement like
strcpy(thisItem.details.fieldDesc,"The field description");

Are they any other ways to load this constant data?

Graham.

grahamfff

Kosk30-Jul-04 11:54

Kosk

30-Jul-04 11:54

Well you can always do

<br />
typedef struct yadda<br />
{<br />
	yadda()<br />
	{<br />
		strcpy(fieldDesc,"This is a description");<br />
		strcpy(detailsDesc ,"This is a description");<br />
		strcpy(unitsStr ,"This is a description");<br />
<br />
	}<br />
char fieldDesc [100];<br />
char detailsDesc [20];<br />
char unitsStr [10];<br />
}GENERAL_DATA;<br />

Then every new GENERAL_DATA variable will be initialized.

Grahamfff30-Jul-04 21:07

30-Jul-04 21:07

Thanks for the info, that solves the first problem.

But can you advise on how to use a union or other overlay method.
I just want to deal with a buffer when sending out the data, but deal with the structure itmes in the program; i.e. two names for the same item of data; see listing below

typedef struct yadda<br />
{<br />
	yadda()<br />
	{<br />
	strcpy(fieldDesc,"This is a description");<br />
	strcpy(detailsDesc ,"This is a description");<br />
	strcpy(unitsStr ,"This is a description");<br />
<br />
	}<br />
	char fieldDesc [100];<br />
	char detailsDesc [20];<br />
	char unitsStr [10];<br />
}GENERAL_DATA;<br />
<br />
typedef struct <br />
{<br />
	unsigned short	data; <br />
	GENERAL_DATA	details;<br />
}ITEM_DATA;<br />
<br />
union DATA01<br />
{<br />
	ITEM_DATA thisSignal;<br />
	unsigned int buffer[512];<br />
}data01;

I get the error c:\Overlays\OverlaysDlg.cpp(48): error C2620: member 'SIGNAL1::thisSignal' of union 'SIGNAL1' has user-defined constructor or non-trivial default constructor.

Are they another method of overlaying the data.

grahamfff

Gary R. Wheeler30-Jul-04 12:33

30-Jul-04 12:33

If this is C++, you should add constructors to both struct's to handle the initialization. If this is 'plain old' C (which I guessed might be the case, from your use of typedef), you can try the following:

// General part of the Structure (used many times)
typedef struct 
{
    char fieldDesc [100];
    char detailsDesc [20];
    char unitsStr [10];
} GENERAL_DATA;
// The main structure
typedef struct 
{
    unsigned short data; // Dyanamic data
    GENERAL_DATA details; // Static data
}ITEM_DATA;
static ITEM_DATA InitialItemData = {

    1234,                 // 'unsigned short data' in the ITEM_DATA struct
    {
        "field description",    // char fieldDesc[100]
        "detail",               // char detailsDesc[20]
        "units"                 // char unitsStr[10]
    }
};

Anywhere you need to initialize an ITEM_DATA, just assign it:

ITEM_DATA current_item;
current_item = InitialItemData;

Software Zen: delete this;

Grahamfff30-Jul-04 21:32

30-Jul-04 21:32

Thanks for the info and yes was for C code. Just two points, how would you do it for C++ and can you overlay the structure via union;

union DATA01<br />
{<br />
	ITEM_DATA thisSignal;<br />
	unsigned int buffer[512];<br />
}data01;

i.e. same data by two different names.

grahamfff

Gary R. Wheeler31-Jul-04 1:55

31-Jul-04 1:55

For C++, I would add a constructor. In C++, class and struct are the same except for one point. With struct, members have public access by default, while with class, the access is private by default. This means that a struct can have a constructor, and that's the place you should initialize the values.

You can initialize the union as follows:

data01.thisSignal = ItemDataInitial;

where ItemDataInitial is an initialized ITEM_DATA as I described in the previous post. If you use a constant initializer for the union, it must correspond to the first field in it.

Software Zen: delete this;

Grahamfff2-Aug-04 10:50

2-Aug-04 10:50

Thanks for the info. I have started to use your scheme, or a varient of it.

Will use the union as follows:-

typedef struct
{
unsigned short data1;
}DATA1;
typedef struct
{
unsigned : 4 data2;
}DATA2;

etc

union ALL_DATA_UNION
{
DATA1 data1;
DATA2 data2;
etc
unsigned short buffer[50];
}ALL_DATA;

I need to transmit the buffer, but want all the data items 'overlayed' with the buffer. Dont need to initialise the union as can use memcpy to zero the buffer.

I will have another structure with the details of each item of data and initialise it as per your scheme.

Thanks again, but please point out if this scheme is fault.

Regards,

Graham

grahamfff