c++ - What does operator << do in this line?

Question

I can not understand what this line does:

fBuffer[fByteIndex] += 1 << (fBitIndex - 1);

where:

unsigned char fBuffer[32];
int fBitIndex;

and:

for ( int i = 0; i < 32; i++ )
     fBuffer[i] = 0;

fBitIndex = 8;

What << does there?

Answer 1

<< is the left-shift operator, and assuming fBitIndex is 8 the code

fBuffer[fByteIndex] += 1 << (fBitIndex - 1);

is equivalent to

fBuffer[fByteIndex] += 128;

Why? Because a left-shift means you shift the bits of the value "left"; in your case, 00000001 (1), is shifted left 7 times, becoming 10000000 (128).