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I should know that ... thank you.
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Good idea. I have few troubles with accessing USB drive with CFile, but once I'll solve it, the code will be simple.
Here is my trial, none on them has worked:
file.Open(_T("\\\\.\\F:"), CFile::modeRead | CFile::osSequentialScan);
file.Open(_T("F:"), CFile::modeRead | CFile::osSequentialScan);
file.Open(_T("F:\\"), CFile::modeRead | CFile::osSequentialScan);
HANDLE hVolume = ::CreateFile(sVolume, GENERIC_READ,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL, OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, NULL);
CFile file(hVolume);
CFileStatus status;
file.GetStatus(status);
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When using CFile::Open you should pass the CFileException* parameter to get the failure cause if CFile::Open fails.
See the example in CFile::Open
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It is just the same as OpenFile behind the scenes so nothing to do with CFile. Your call probably fails because you are not including the share flags in your call to CFile::Open(), which are required when trying to access a device.
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As others have pointed out, the issue is with pBuffer not associated with any allocated memory.
In addition to this, I would like to point out one more flaw in your code, although it doesn't matter in this case.
The third parameter to SetFilePointer[^] must be an address of a LONG variable.
PLONG does not declare a LONG variable. It's only a pointer to a LONG variable.
Here SetFilePointer will actually try to write to memory 0.
What you need to do is declare a LONG variable and provide its address -
LONG highValue; SetFilePointer(..., ..., &highValue, ...); You can also pass a nullptr, if you're not intersted in that value.
«_Superman_»
I love work. It gives me something to do between weekends.
Microsoft MVP (Visual C++) (October 2009 - September 2013) Polymorphism in C
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It will interest me, not this time, but in the real program. I modified the code like this:
LONG lValueLow = 0;
LONG lValueHigh = 0;
if (INVALID_SET_FILE_POINTER == SetFilePointer(hVolume, lValueLow, &lValueHigh, FILE_BEGIN) &&
NO_ERROR != GetLastError())
{
TRACE("Error: %d\n", GetLastError());
return FALSE;
}
else
{
TRACE("%d\t%d\n", lValueLow, lValueHigh);
}
Thank you Superman !
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You do not need lValueHigh unless the distance to move is a 64 bit value: just specify NULL instead.
Also I suggest you study the difference between a variable and a pointer to a variable, you seem somewhat confused about it.
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Understood now, I didn't paid attention on that function (lpDistanceToMoveHigh, is obviously now, or, at least I think is obviously).
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struct TestStruct
{
int x;
int z;
};
TestStruct S;
TestStruct Funct()
{
return S;
}
Funct().x = 100;
Will this work?
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Yes, but Func() is not really necessary, since you have already declared S. You can just say S.x = 100;
Creating a function to return a structure (or anything else) is usually necessary when you cannot declare the relevant object at compile time, but need to create it dynamically. Something like:
TestStruct* Funct()
{
TestStruct* pS = new TestStruct;
pS->x = 0;
ps->z = 0;
return pS;
}
TestStruct* pNewStruct = Funct();
pNewStruct->x = 100;
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Hello,
the code itself will work, but will not do what I suppose you expect.
Here, Funct returns a copy of the TestStruct S.
So Funct().x = 100 will affect 100 in a temporary TestStruct that you can not use after that.
I don't know why you want to use a function to access your S structure, but the behavior you look for is probably :
TestStruct& Funct()
{
return S;
}
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my actual code:
ChartNode Chart[100];
ChartNode NodeCoord(int x, int z)
{
return Chart[z * 10 + x];
}
if(NodeCoord(4,4).access)
NodeCoord(4,4).access = false;
The result I`m looking for is the same as the result achieved with this function:
void NodeCoord(int x, int z, bool writetobool)
{
Chart[z * 10 + x].access = writetobool;
}
modified 3-May-20 5:10am.
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So you probably need to return a reference :
ChartNode& NodeCoord(int x, int z)
{
return Chart[z * 10 + x];
}
else the NodeCoord(4,4).access = false will assign a temporary copy of your ChartNode struct and not the one in your array.
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ChartNode& NodeCoord() will work for both read and write?
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If you are referring to array cells with two dimension values then you should use a two-dimensional array. As it is you can pass any values in to NodeCoord but there is no way of telling if they are valid. So you could end up with lots of random memory corruption.
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Thanks Richard
How do I declare a two (or more) dimensional array? The problem is I might need arrays with a great number of dimensions. I need a `one fits all` type of solution.
modified 3-May-20 5:42am.
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Just like a one-dimensional, but you declare the two dimensions. Think of it as a block of items having some number of rows and columns. so you could have something like:
#define MAXROW 10
#define MAXCOL 5
ChartNode Chart[MAXROW][MAXCOL];
ChartNode NodeCoord(int row, int column)
{
if (row > 0 && row < MAXROW && column > 0 && column < MAXCOL) {
return Chart[row, column]; }
else
{
return NULL; }
}
All of these features are well documented in the C/C++ documentation and the various tutorials on the language.
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the two dimensional array seems like something too good to be true  The compiler is definitely doing something suspicious behind the courtain.
Thanks.
modified 3-May-20 6:31am.
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I think you could do with studying all the features of C (or C++ if that is what you are using). Trying to learn a language by posting questions here will take ten times as long, and you will still miss most of it.
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Internally it's just continuous memory that is allocated for a 2 dimensional array (For any no. of dimensions for that matter).
The compiler uses the specified dimensions to calculate the offset into the memory to fetch.
For instance, offset of Chart[2][3] could be calculated as -
(sizeof(ChartNode) * MAXROW * 2) + (sizeof(ChartNode) * 3)
«_Superman_»
I love work. It gives me something to do between weekends.
Microsoft MVP (Visual C++) (October 2009 - September 2013) Polymorphism in C
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Often I edit my posts/replies shortly after making them, I can`t organise myself in a single swing.
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