How to read file created by C++ program in java?

I have one file created by c++ program which is in encrypted format. I want to read it in my java program. In case of decryption of file contents, decryption algorithm is performing operations on byte[which is unsigned char-BYTE in c/c+开发者_StackOverflow中文版+]. I used same decryption algorithm which I have used in my c/c++ program. This algorithm contains ^, %, * and - operations on byte. But byte datatype of java is signed because of which I am facing problems in decryption. How can I read file or process read data with 1byte at a time which is unsigned? thanks in advance.

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byte b = <as read from file>;
int i = b & 0xFF;

Perform operations on i as required

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The standard method InputStream.read() reads one byte and fits it into a int, so in practice it is an unsinged byte. There are no unsigned primitive data types in java, so the only approach is to fit it in an upper primitive.

That being said you should have no trouble performing encryption/decryption over data bytes read from the file, since the bytes are the same, no matter if they are interpreted as signed or unsigned (0xFF can be 255 or -1). You say the alghorithm contains "^, %, *", etc. That is an interpretation of raw bytes, taking into account a character encoding (that fits 8 bit per character I suppose). You should not perform encryption/decryption operations over other than raw bytes.

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First, InputStream.read() returns an int but it holds a byte; it uses an int so -1 can be returned if the EOF is reached. If the int is not -1, you can cast it to byte.

Second, there are read() metods that allow storing the bytes directly in a byte[]

And last, if you are going to use the file as a byte[] (and it is not too big) maybe it would be interesting copying the data from FileInputStream and write it into a ByteArrayOutputStream. You can get the resulting byte[] from the late object (note: do not use the .read() method, use .read(byte[], int, int) for performance).

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Since there is no unsigned primitive type in Java, I think what you can do is to convert signed byte into integer (which will virtually be unsigned because the integer will always be positive). You can follow the code in here: Can we make unsigned byte in Java for the conversion.