Obtaining an integer given its 4-byte unsigned integer little-endian form? (C++)

I'm probably very wrong here so please point out any misconceptions or mistakes I may have.

The input for this assignment is a string of some characters followed by a series of 4-byte unsigned integers in little-endian form. I read the input into an STL string, and used the substring function to isolate just the integers into a new string.

From what I understand, the least significant bits will be stored starting from the left most byte. An unsigned integer 131071开发者_如何转开发(dec) whose binary representation is (0000 0000 0000 0001 1111 1111 1111 1111) would then be stored as 1111 1111 1111 1111 0000 0001 0000 0000

Parsing this new string 4 bytes at a time, I thought the first byte would contain the bits for values 0-255, 2nd byte for 256-65535 and so forth for the 3rd and 4th bytes.

I took the 1st byte, casted it to an unsigned int, and then shifted it 24 bits, I did the same to the 2nd and 3rd bytes, except 16 and 8 bit shifts respectively.

I got 255 and 65535 for the 1st and 2nd bytes as expected, but 0 for the 3rd byte. I believe I have to use the & operator somewhere, but I can't figure out where. If anyone could give me some advice, or perhaps a less foolish way of accomplishing the same task, I would greatly appreciate it.

If you got 0 for the 3rd byte, and your data matches your description, there's a bug in your code. The below code will correctly convert your sample data.

// Data from file
unsigned char Buffer[] = { 255, 255, 1, 0 };

// Convert the LSB data to an unsigned int
unsigned int Result = 0;
for (int i = 0; i < 4; ++i) {
  Result |= static_cast<unsigned int>(Buffer[i]) << (i*8);
}