在C ++中将0和1的char数组转换为字节

Question

I have a question here. It might sound trivial to you but not for me since I'm pretty much still a noob in C++. (also sorry for my limited english knowledge)

Let's say I have a char a[72] array. This array is filled with '0' and '1' representing bits ( a[0] = '0' , a[1] = '1' , a[2] = '1' etc.) and I need to save this as a binary file, so when I try to view this file with xxd -b i would like to see these 9 bytes as they were in the array.

Could please anybody lead me to the solution how to convert this char array?

Answer 1

You need to split your array in groups of 8 symbols and convert each group from binary string representation to unsigned char. For example:

unsigned char byte = 0;
for( int i = 0; i < 8; ++i )
    if( a[i] == '1' ) byte |= 1 << (7-i);

Then put that bytes into another array size 72/8 and store it into file, for example by std::ostream::write() method. You may group bits by 16, 32 or 64 bits and use uint16_t , uint32_t or uint64_t for values, but this way is most simple and you probably should start with it and make it work first.

Answer 2

Perhaps something like this?

const std::size_t n = 72;
std::vector<char> byteArray(n / 8);

for (std::size_t i = 0; i < n / 8; ++i)
    for (std::size_t j = 0; j < 8; ++j)
        if (a[i * 8 + j] == '1')
            byteArray[i] |= 1 << j;

Then access byteArray with operator[]() or data() .