CODEWITHSUNDEEP
c++memoryint32-bit
Coder1337
Coder1337

Reputation: 159

C++ Split Int Into 4 Parts (32 Bit Machine)

Alright so If I have an int like this (used to store a line of ASM)

int example = 0x38600000; //0x38600000 = li r3, 0

How would I split this int into 4 seperate sections? I've come up with this

int example = 0x38600000;
char splitINT[4];
for(int i = 0; i < 4; i++)
{
    splitINT[i] = *(char*)(((int)&example + (0x01 * i)));
}
//splitINT[0] = 0x38;
//splitINT[1] = 0x60;
//splitINT[2] = 0x00;
//splitINT[3] = 0x00;

The above code actually works perfectly fine when reading memory from the process my executable is running within, but this does not work when trying to read the programs own memory from within itself like shown in the code example above.

So how else would I go about splitting an int into 4 separate parts?

Upvotes: 1

Views: 2587

Answers (3)

Daniel
Daniel

Reputation: 1287

Your code is really confusing since I am not sure why it works at all given the cast to int in the statement. You can read each individual byte of the 32-bit int by casting it to a char *, where a char is the size of one byte on your machine.

int example = 0x38600000;
char *bytepointer = reinterpret_cast<char*>(&example);
for(int i = 0; i < 4; i++)
{
    std::cout << static_cast<int>(bytepointer[i]) << " ";
}

std::cout << std::endl;

You can also use bytepointer to modify the memory contents of the int byte by byte.

Additionall, you should also look up the role of endianness in determining the memory layout of integers. A machine can choose to use a big- or small-endian layout, and this will change the order in which the bytes are printed and how you can modify the int.

Upvotes: 2

user3344003
user3344003

Reputation: 21607

unsigned char c1 = static_cast<unsigned char>(example & 0xFF) ;
unsigned char c2 = static_cast<unsigned char>((example >> 8) & 0xFF) ;
unsigned char c3 = static_cast<unsigned char>((example >> 16) & 0xFF) ;
unsigned char c4 = static_cast<unsigned char>((example >> 24) & 0xFF) ;

Upvotes: 1

ttemple
ttemple

Reputation: 882

union split_union
{
    int as_int;
    char as_char[4];
}

// either initialize like this...
split_union example{0x38600000};

// or assign like this...
split_union ex;
ex.as_int = 0x38600000;


//example.as_char[0] = 0x00;
//example.as_char[1] = 0x00;
//example.as_char[2] = 0x60;
//example.as_char[3] = 0x38;
// correct order for Visual Studio on x86.

Upvotes: 1

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