How to give variable input to serail port

Question

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C++

CString itemno;

UpdateData(TRUE);

itemno.Format("%x",m_itemno);// here m_itemno is integer in range 0 to 100

int  len = itemno.GetLength();

if(len == 1)

itemno = "0x0" + itemno;

if(len == 2)

itemno = "0x" + itemno;



unsigned char data[1] = itemno; // Here I  get problem;

~~~code for CreateFile etc~~~

bool retval = WriteFile(hport,data,1,&byteswritten,NULL);

//I have to send only 1 byte of data

Now the problem I am facing is that I am unable to convert from CString to

C++

unsigned char data[1].

If for example if m_itemno is 12,then its hexadecimal equivalent is 0x0c

if I write unsigned

C++

char data[1] = {0x0c}

,everything works fine but it is like hardcoding

but I want it done programatically so that I can enter any number between o to 100;

How to do it ?

Posted 21-Jun-12 17:53pm

adityarao31

Updated 21-Jun-12 18:11pm

Prasad_Kulkarni

v2

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2 solutions

Solution 2

My problem got solved by using following code snippets

C#

CString Class::IntToHex(int* yourint)

{
unsigned char ch[1];
Cstring output;
memcpy(ch,yourint,sizeof(int));
retVal = WriteFile(hPort,ch,1,&byteswritten,NULL);
}

CString Class::FloatToHex(float* yourfloat)
{
unsigned char ch2[4];
Cstring output;

memcpy(ch2,yourfloat,sizeof(float));
retVal = WriteFile(hPort,ch2,4,&byteswritten,NULL);
}

Posted 21-Jun-12 21:41pm

adityarao31

Updated 21-Jun-12 21:42pm

v2

Comments

Jochen Arndt 23-Jun-12 4:55am

Copying the binary data using memcpy is not necessary. Just pass them as they are to WriteFile:
WriteFile(hPort, yourint, 1, &byteswritten, NULL);
WriteFile(hPort, yourfloat, sizeof(float), &byteswritten, NULL);
Your code contains a buffer overrun in IntToHex when copying 4 bytes (sizeof(int)) to the buffer ch which has a size of 1. The only reason why your code does not crash is the existance of the unused local variable CString output that is overwritten by memcpy.

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Jochen Arndt · Accepted Answer · 2012-06-21T21:19:00

You want to send a binary data byte containing a (decimal) number in the range of 0 to 100 (0x64). Your member variable m_itemno already contains this value. So you might use this:

C++

unsigned char data = static_cast<unsigned char>(m_itemno & 0xFF);
bool retval = WriteFile(hport,&data,1,&byteswritten,NULL);

Because Intel processors use Little-Endian byte order (least significant byte is stored at lowest address) you may even use:

C++

bool retval = WriteFile(hport,&m_itemno,1,&byteswritten,NULL);