How to convert int to byte in C?

Question

I would like to convert an int to a byte in C.

In Java, I'd write:

int num = 167;
byte b = num.toByte(); // -89

In C:

int num = 167;
???

Answer 1

byte is a java signed integer type with a range of -128 to 127. The corresponding type in C is int8_t defined in <stdint.h> for architectures with 8-bit bytes. It is an alias for signed char.

You can write:

#include <stdint.h>

void f() {
    int num = 167;
    int8_t b = num;  // or signed char b = num;
    ...

If your compiler emits a warning about the implicit conversion to a smaller type, you can add an explicit cast:

    int8_t b = (int8_t)num;  // or signed char b = (signed char)num;

Note however that it is much more common to think of 8-bit bytes as unsigned quantities in the range 0 to 255, for which one would use type uint8_t or unsigned char. The reason java byte is a signed type might be that there is no unsigned type in this language, but it is quite confusing for non-native readers.

byte can also be defined as a typedef:

typedef unsigned char byte;  // 0-255;

or

typedef signed char byte;    // -128-127;

Do not use type char because it is implementation defined whether this type is signed or unsigned by default. Reserve type char for the characters in C strings, although many functions actually consider these to be unsigned: strcmp(), functions from <ctype.h>...