C++ 扩展 Ascii 和负值

Question

I am trying to read some values from a binary file. I read byte by byte. I just want to store each int value from a certain char into a buffer, sized as the number of bytes contained in the file..So I expect to have values between 0 and 255 stored int the buffer. But I am getting some negative ones some times..Does anyone know how can this problem be fixed? I would appreciate your response.

Answer 1

I expect to have values between 0 and 255 stored int the buffer.

This suggests you want the value range of unsigned char .

But I am getting some negative ones some times

This suggests you are reading signed values. The computer will not do something you do not tell it to do. If you don't want signed values, don't allow that possibility. The signed char type allows negative values, the char type may (depending on the system) allow negative values, and the unsigned char type does not allow negative values. Simply choose the correct tool for the job at hand.

It's just a guess without seeing your code, but I'm pretty sure you are using an array of char for your buffer when you should be using either an array of unsigned char or an array of std::byte (a type that implements the concept of a byte without the baggage of interpreting bytes as characters, useful when reading a binary file).