Read values from unsigned char bytestream in C++

Question

my task is to read metadata values from a unsigned char array, which contains the bytes of a binary .shp file (Shapefile)

unsigned char* bytes;

The header of the file which is stored in the array and the order of the information stored in it looks like this:

int32_t filecode // BigEndian
int32_t skip[5] // Uninteresting stuff
int32_t filelength // BigEndian
int32_t version // LitteEndian
int32_t shapetype // LitteEndian
// Rest of the header and of the filecontent which I don't need

So my question would be how can I extract this information (except the skip part of course) under consideration of the endianness and read it into the according variables.

I thought about using ifstream, but I couldnt figure out how to do it properly.

Example:

Read the first four bytes of the binary, ensure big endian byte order, store it in a int32_t. Then skip 5* 4 Bytes (5 * int32). Then read four bytes, ensure big endian byte order, and store it in a int32_t. Then read four bytes, ensure little endian byte order, and again store it in a int32_t and so on.

Thanks for your help guys!

Answer 1

So 'reading' a byte array just means extracting the bytes from the positions in the byte array where you know your data is stored. Then you just need to do the appropriate bit manipulations to handle the endianess. So for example, filecode would be this

filecode = (bytes[0] << 24) | (bytes[1] << 16) | (bytes[2] << 8) | bytes[3];

and version would be this

version = bytes[13] | (bytes[14] << 8) | (bytes[15] << 16) | (bytes[16] << 24);

(An offset of 13 for the version seems a bit odd, I'm just going on what you stated above).