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How to convert from char to unsinged char

Posted on 2004-09-01
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Last Modified: 2013-11-20
Hi, Expert,

I need user enter decimal number into edit box, e.g. 0 to 511, say 511 (this is ascii number), I need conver 511 into hex number into variable unsigned char array[0] = 0xff, unsigned char array[1] = 0x01 since 511d is 1ffh.
I can transmit this array out through serial port.

Thanks,
Ben
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Question by:benlian888
7 Comments
 

Author Comment

by:benlian888
ID: 11959229
I am using VC++  6.0
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LVL 55

Expert Comment

by:Jaime Olivares
ID: 11959688
I will exploit some WINAPI macros in my solution:

first you have to conver the hex string  to a numeric variable:

DWORD h;
sscanf(yourcontroltext, "%x", &i);

but h is a 32-bit value. Since I assume you want to transmit value, assign it to another variable:
WORD n = LOWORD(h);

then copy binary content to a char array in the order you want:

char array[2];
array[0] = HIBYTE(n);
array[1] = LOBYTE(n);



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LVL 7

Expert Comment

by:vijay_visana
ID: 11960481
it should be
   sscanf(yourcontroltext, "%x", &h);
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LVL 19

Expert Comment

by:drichards
ID: 11960775
>> first you have to conver the hex string  to a numeric variable

It is not a hex string.  You want a %d format rather than a %x:

      sscanf(yourcontroltext, "%d", &h);

Hex string would be 0x1ff or at least 1ff.



Alternative code if you are using Winsock (need it for htons):

    unsigned short val = (unsigned short)::atoi(numText);
    val = ::htons(val);
    unsigned char *bytes = (unsigned char*)&val;
    // And optionally, if you really want the bytes in a real array...
    char data[2] = { bytes[0], bytes[1] };
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LVL 14

Accepted Solution

by:
wayside earned 300 total points
ID: 11967165
I like to use bitmasks directly instead of the macros, and atoi() is easier than sscanf:

int number = atoi(yourcontroltext);

char data[2];

data[0] = number & 0xff;
data[1] = (number & 0xff00) >> 8;
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