string manipulation problems

I'm having problems with this line of the code:

Code:

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txtCompareResults = lstrcmp((LPCWSTR) argv[1], TEXT("-name"));

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My problem is that when argv[1] is "-name", lstrcmp doesn't return a value of 0, which means that the texts are identical. Does anyone know why that may be the case?

how are you declaring main?

Code:

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void main(int argc, char* argv[])

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Could the void keyword be why?

um, no. but argv is an array of char - not wchar_t. you'll need to either declare a wide-character main (eg: int wmain( int, wchar_t**)) or convert (not cast) the command line parameters to wchar_t strings.

Is there a standard function/API method in Windows where I can perform the conversion or do I have to implement it myself?

There's MultiByteToWideChar, but what for? The source string is narrow, you're comparing against a literal that contains nothing but basic characters, so just use narrow strings and strcmp. (Or lstrcmpA, if you don't want the CRT dependency.)

Thanks for the heads up on strcmp.

Never use void main: http://cpwiki.sourceforge.net/Void_main

There apparent appears a case where I would have to carry out the conversion. Here is some code example:

Code:

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        // Convert the ANSI argument for the pDriverName
        // to UNICODE
        char* pDriverName = "Some Name";
        LPWSTR pDriverNameW = NULL;
        pDriverNameW = (LPWSTR) malloc(sizeof(pDriverName));
        MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED,
                pDriverName,
                sizeof(pDriverName),
                pDriverNameW,
                sizeof(pDriverName)
                );
        wcout << "pDriverNameW = " << pDriverNameW << endl;

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I have tried to fiddle with the size parameters of the function, but I can never seem to convert properly. It just converts the first string: "Some♠". Does anyone know about what's going on with the MultiBytetoWideChar function call (I found that the problem is how I called this function)? Thanks.

The problem is that sizeof(pDriverName) gives you the number of bytes in the platform's pointer, not how big the string is.

What you should do is this:

Code:

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const char *pDriverName = "Some Name"; // Never assign string literals to non-const pointers.
int size = MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, pDriverName, -1, 0, 0);
if(size == 0) {
  // handle error - this shouldn't ever happen
}
WCHAR *pDriverNameW = new WCHAR[size]; // or (WCHAR*)malloc(size * sizeof(WCHAR) for C.
// if using malloc, handle allocation error
MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, pDriverName, -1,
  pDriverNameW, size);

// ...

delete[] pDriverNameW;

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Thanks for the tip. Haven't noticed this reply until now. And it worked quite nicely. Do a lot of win32 functions work like this (first function call to know how much memory to allocate and then perform the actual operation on the second try)?

Not all of them, but some do. Be sure to read the manual.

I have been trying a similar string manipulation code below, but I have been getting an error with my instantiation of flist with the error

Code:

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1>e:\test\installer\installer.cpp(105) : error C2057: expected constant expression
1>e:\test\installer\installer.cpp(105) : error C2466: cannot allocate an array of constant size 0
1>e:\test\installer\installer.cpp(105) : error C2075: 'flist' : array initialization needs curly braces

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Code:

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int flist_num = argc - INSTARGC;
if (flist_num > 0)
{
        wstring flist[flist_num] = 0;
        for (DWORD i = 0; i < flist_num; i++)
        {
                size = MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, argv[i+INSTARGC], -1, 0, 0);
                if(size==0)
                {
                        wcout << "Error occurred when trying to allocate memory for conversion"
                                << endl;
                }
                tempPrinterName = new WCHAR[size];
                MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, argv[i+INSTARGC],
                                                -1, tempPrinterName, size);
                flist[i] = wstring(tempPrinterName);
                delete[] tempPrinterName;
                wcout << flist[i] << endl;
                }
}

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My trouble is that I don't really know what would be in the contents of flist until I have finished processing the arguments passed in the main function. Would I need to have some type of variable arrays to do this?

wstring flist[flist_num] = 0;

You cannot dynamically allocate an array this way in C++. It must be a size that is known at compile time and obviously it isn't, so you get an error.
Another way to do it is to make it a std::vector<wchar_t> and call .resize().
Remember that Win32 API takes C-style strings, not C++ strings, so it must be wchar_t, NOT wstring.

Thanks for your help regarding using vectors to get around the problem. I have one more question regarding another type of manipulation:

Code:

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#include <windows.h>
#include <iostream>
#include <string>
using namespace std;

int main()
{
        WCHAR resultant[64];
        const WCHAR* someName = L"Black Panther";

        resultant = someName;

        system("pause");

        return 0;
}

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Supposedly I tried to do something like above in a bigger project, but I'm getting an error like

Code:

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1>e:\test\copydriverfiles\copydriverfiles.cpp(11) : error C2440: '=' : cannot convert from 'const WCHAR *' to 'WCHAR [64]'

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I'm trying to copy someName into resultant, or at least the contents to be copied. Is there anything seriously wrong with what I'm trying to do?

Realize that someName is a pointer, and resultant is an array.
A pointer is a variable that contains an address. How can you assign an address to an array? Ponder on that. It should be trivial if you understand how arrays and pointers work.

Thanks for pointing out the differences between pointers and array. I was taking that the transfer between the two variables for granted, assuming that the two variables were both pointers. Would the only way of transferring the contents be transferring what the pointer dereferences one by one until the pointer is pointing to a null character?

Quote:

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Originally Posted by stanlvw

Thanks for pointing out the differences between pointers and array. I was taking that the transfer between the two variables for granted, assuming that the two variables were both pointers.

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Oh yes, it would work just fine, but an array isn't a pointer, so that's where the problem lies.

Quote:

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Would the only way of transferring the contents be transferring what the pointer dereferences one by one until the pointer is pointing to a null character?

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Yes! Your mind is clever :)
That's exactly what string copy functions do.
strcpy for char and wcscpy for wchar_t.

Thanks for the tip on the strcpy functions. They worked quite nicely.

That's what they were designed to do ;)