Is there potentially an endianness trouble here?

Question

I would like to write a function such as putchar, with the help of write function.

#include <unistd.h>

ssize_t f(int fd, int c) {
    return write(fd, &c, 1);
}

But I think there could be an endianness problem here, isn't it ? So should I use sizeof (int) ? I am a bit confused, I don't know how to process (need a cast to unsigned char ?).

Answer 1

Yes, there is potentially an endianness problem here. The cure is to pass c as an unsigned char rather than as an int.

ssize_t
f(int fd, unsigned char c)
{
    return write(fd, &c, 1);
}

The <stdio.h> routines work with ints mostly for historical reasons. They are very old, and contain many interface design decisions that would be considered incorrect nowadays. Do not use them as a template.

Answer 2

Yes, good catch, there is an endian problem. If you want to keep the function signature, you need to temporarily store the data into an unsigned char and then output it;

#include <unistd.h>

ssize_t f(int fd, int c) {
    unsigned char ch = (unsigned char)c;
    return write(fd, &ch, sizeof(unsigned char));
}