Question

I want to read unsigned char from file and have search many different ways to execute. But I don’t know the reason why they work or don’t work.

1.
ifstream input(ios::in | ios::binary) //seems to not work, but why?

I have set the ios::binary which supposed to prevent the conversion.

2.
unsigned char buffer[BUFFER_SIZE];

myfile.read((unsigned char *) buffer, BUFFER_SIZE);//error!fail

myfile.read((char *) buffer, BUFFER_SIZE);//work, the data type is unsigned char

why do I have to convert it to char*?
The data stored in the array won’t be converted to char not unsigned char?
What does it do during conversion?

3.
vector//it work but I don’t know what it have done.

Answer 1

For the first part, the constructor also expects a file name. For example,

ifstream input("myfile.dat", ios::in | ios::binary);

I believe you can omit the ios::in, as it is the default for ifstream.

And for the second part, istream::read expects a char* pointer (or some equivalent type). After reading the data, you can cast the elements to unsigned char*.