将unsigned long转换为char *，而忽略高0字节

Question

I have an unsigned long long variable which I want to write to a binary file. However, I need to neglect all leading bytes which are zero.
This means

unsigned long long toWrite = 4;

should write 0x04 and not 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x04 to the stream.

#include <fstream>
int main(){
  std::ofstream out("test.txt", std::ios::binary);
  unsigned long long toWrite = 4;
  out << cutoffZeroBytes(toWrite);
  out.close();
  return 1;
}

I was thinking about making cutoffZeroBytes a function which returns a char* . But if there are zero bytes in the middle (eg 0x03 0x00 0xf1), then I think I couldn't write it to the stream, since 0x00 determines the end of an char array. I'm a little clueless here and need some help.

Answer 1

One way is using write for this aim. So, just change:

out << cutoffZeroBytes(toWrite);

to:

out.write((char*)&toWrite, sizeof(toWrite));

And if you want to cut this number:

char* start = (char*)&toWrite;
int pi = sizeof(toWrite);
for (; pi > 0; pi--, start++)
    if (*start)
        break;
out.write(start, pi);