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Hello. How do I extract RGB colors from a byte ? Thanks
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If you have 1 byte representing a color then it is probably just the index of the full RGB color inside the corresponding palette.
Veni, vidi, vici.
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Just mask the bits[^] out 
(do you still need some help ?)
They sought it with thimbles, they sought it with care;
They pursued it with forks and hope;
They threatened its life with a railway-share;
They charmed it with smiles and soap.
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I want to use a pointer to get an array elements value.
char s1 = {1,2,3,4,5,6,7};
int t1 = *(int*)(&s1[2]);
I think t1 value is 3456,but in fact, it returns a strange value looks like an address value.
But I make a struct type like:
struct TestStruct {
char c1;
char c2;
char c3;
char c4;
}ts1;
ts1 = *(TestSTruct*)(&s1[2]);
then I can get ts1.c1 = 3, ts1.c2 = 4, ts1.c3 = 5,..
Can anybody give me some hint?
modified 13-Dec-13 2:19am.
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In both cases your syntax seems to be somewhat confused. For case 1 why not just:
char s1[] = {1,2,3,4,5,6,7};
int t1 = s1[2];
In case 2, you are casting an array to a structure which will in many cases break your code. Structures will often have their elements aligned on word boundaries so what you think is elemnt n of the array is actually something completely different. If you want to use a structure then fill it with your data in the first place. Don't use casts unless you know that the data will be in the locations you think it will.
[edit]
Added [] after s1, as Stefan pointed out.
[/edit]
Veni, vidi, abiit domum
modified 13-Dec-13 5:00am.
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shouldn't this be
char* s1 = {...};
rather than
char s1 = {...};
?
The latter is just a single char, and using s1 as an array will lead to invalid memory references; most likely such attempts will access arbitrary adresses on the stack (i. e. other stack variables or parts of them).
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
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Forgot to indicate, s1 is a global array.
In fact, I tested, the method works, the weird value is because I use %d to print, when i change %d to %x, it prints correct result
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My point was that the code you posted produces a compiler error in line 1. I suggested you should correct it in your posting so we can see what you your code really looks like, rather than guessing what it might be.
The difference between %d and %x is that the former expects a signed integer variable and prints it as such, whereas the latter will completely ignore the type of the variable and print whatever it finds in unsigned hexadecimal. In general, I doubt that is what you wanted, although for values lower than 10 it may look like it. If %d produces a different output than %x for a variable of type char, then the only relevant difference is signed/unsigned, so %ud shoud print the same as %x.
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
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econy wrote: then I can get ts1.c1 = 3, ts1.c2 = 4, ts1.c3 = 5,..
Note that there is no guarantee the compiler will lay out struct members in the exact same order you defined them.
econy wrote: ts1 = *(TestSTruct*)(&s1[2]);
There is no guarantee this will work as expected with any modern compiler, especially if that struct contains more than just four chars. The compiler may have to modify the total memory layout depending on padding, virtual function table, base classes, and debug information (and possibly for other reasons, too).
If you want a clean solution, just provide a simple constructor and maybe assignment operator:
struct TestStruct {
TestStruct(const char c1_, const char c2_, const char c3_, const char c4_)
: c1(c1_), c2(c2_), c3(c3_), c4(c4_)
{
}
TestStruct(const char* s)
{
operator=(*s);
}
TestStruct* operator=(const char* s)
{
if (s != nullptr)
{
c1 = c1_;
c2 = c2_;
c3 = c3_;
c4 = c4_;
}
return *this;
}
...
};
You can then initialize your structs in any of the following ways:
const char* s1 = {1, 2, 3, 4, 5, 6, 7};
struct TestStruct ts1(3, 4, 5, 6);
struct TestStruct ts2(s1+2);
struct TestStruct ts3;
ts3 = s1+2;
Please note that this last assignment may lead to unintentional errors if used carelessly. but at least it's readable and extendable.
[edit]
Sorry, I just noted that you asked about C, not C++. For C, most of my concerns expressed above don't apply! Your assignment statement is essentially correct in that case (although you could simplify &s1[2] to s1+2 if you want to)
[/edit]
GOTOs are a bit like wire coat hangers: they tend to breed in the darkness, such that where there once were few, eventually there are many, and the program's architecture collapses beneath them. (Fran Poretto)
modified 13-Dec-13 5:46am.
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Since 64-bit C++ code does not allow inline assembly instructions, how can I execute a jmp instruction when I need to?
The difficult we do right away...
...the impossible takes slightly longer.
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Why would you need to?
Veni, vidi, abiit domum
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Richard MacCutchan wrote: Why would you need to?
I want to transfer control to a different function without disturbing the stack. (Without pushing anything more onto it.
The difficult we do right away...
...the impossible takes slightly longer.
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// how can I execute a jmp instruction when I need to?
1. Organize a buffer for the JMP executing
enum {
#ifndef _WIN64
jmpAddrIdx = 2, jmpLen = 10, #else
jmpAddrIdx = 3, jmpLen = 16, #endif
};
static BYTE jmp[jmpLen] = {
#ifdef _WIN64
0x50, 0x48, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x48, 0x87, 0x04, 0x24, 0xc3 #else
0x50, 0xb8, 0x00, 0x00, 0x00, 0x00,
0x87, 0x04, 0x24, 0xc3 #endif
};
2. Fill the address part there in (low Bytes first)
memcpy(&jmp[jmpAddrIdx], YOUR_DESIRED_ADDRESS, sizeof(DWORD_PTR));
3. Take the pointer of an existing global function(void) (Long enough: see jmpLen above)
4. Mark the addressed space of the function as writeable
DWORD dwOldMode(0);
if (VirtualProtect(pfnYourShellFcn, jmpLen, PAGE_EXECUTE_READWRITE, &dwOldMode)) {
5. Write the jump into the function
memcpy(pfnOriginal, jmp, jmpLen);
6. Mark the space as original
VirtualProtect(pfnYourShellFcn, jmpLen, dwOldMode, &dwOldMode);
7. Call the pointed function
(*pfnYourShellFcn)()
8. Be thrilled.
They sought it with thimbles, they sought it with care;
They pursued it with forks and hope;
They threatened its life with a railway-share;
They charmed it with smiles and soap.
modified 13-Dec-13 7:25am.
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That's a great answer. Thanks! 
The difficult we do right away...
...the impossible takes slightly longer.
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I'm thrilled.
Veni, vidi, vici.
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I did think of that, however I don't know if it works across functions.
The difficult we do right away...
...the impossible takes slightly longer.
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Hey hi to all.....I am looking for some basic C tutorials for gaining C language knowledge.
Thanks.
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A Google search[^] finds you plenty. Although your time may be better spent learning C++, or even C#. It is largely a question of what area of development you plan to work in.
Veni, vidi, abiit domum
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A android-phone connect to PC by USB line, I hope to get the nowtime screen picture and show it on the dialog. Are there any ideas to do this??
Now, I get "dev/fb0" file(by "adb push /dev/graphics/fb0"), how should I do to convert to an image?
If my way is wrong, please tell me how to do this??
This is my first question on the Codeproject, please help me !! 
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Hi,
I am using MFC. I want to draw a color filled object (for example, circle) to show on the top of everything else?
Best,
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