Writing values as an arbitrary amount of bits into a byte buffer in C++ - c++

Question

Hey, I need to pack bit values into a byte buffer in C++. My Buffer class has a char array and a position, similar to Java's ByteBuffer. I need a good way to pack bits into this buffer, like so:
void put_bits(int amount, uint32_t value);
It needs to support up to 32 bits. I've seen a solution implemented in Java (that requires start/end access methods before bits can be packed) but I'm not sure how to do this in C++ because the endianness and other low level factors aren't hidden like they are in Java.
I have an inline function declared as endianness() which returns 0 (defined as BIG_ENDIAN) or 1 (defined as LITTLE_ENDIAN) that can be used, but I'm just not sure how to properly pack bits into a byte buffer.
This is the Java version of what I need to implement:
public void writeBits(int numBits, int value) {
int bytePos = bitPosition >> 3;
int bitOffset = 8 - (bitPosition & 7);
bitPosition += numBits;
for(; numBits > bitOffset; bitOffset = 8) {
buffer[bytePos] &= ~ bitMaskOut[bitOffset];
buffer[bytePos++] |= (value >> (numBits-bitOffset)) & bitMaskOut[bitOffset];
numBits -= bitOffset;
}
if(numBits == bitOffset) {
buffer[bytePos] &= ~ bitMaskOut[bitOffset];
buffer[bytePos] |= value & bitMaskOut[bitOffset];
}
else {
buffer[bytePos] &= ~ (bitMaskOut[numBits]<<(bitOffset - numBits));
buffer[bytePos] |= (value&bitMaskOut[numBits]) << (bitOffset - numBits);
}
}
Which requires these two methods as well:
public void initBitAccess() {
bitPosition = currentOffset * 8;
}
public void finishBitAccess() {
currentOffset = (bitPosition + 7) / 8;
}
How should I go about solving this? Thanks.
EDIT: I also still need to be able to write normal bytes before and after writing bits.

Answer 1

Just remove all the public keywords, and I would say that you have your C++ implementation right there.

Answer 2

As long as you use the byte buffer only as such, you can translate the Java code one-to-one. It only gets dangerous if you interpret a byte pointer as another type and try to store a complete int in the byte buffer.
You don't even need the endianness function in this case, since you store a byte in a byte buffer, and there is nothing to convert or adjust size or whatever.