问如何在unistd.h中使用write()和read()

EN

#include <unistd.h>
#include <string.h>

int main (void) {
    size_t input_size = 50;
    // "+ 1" is for storing '\0'
    char buffer[input_size + 1];
    // We don't use the return value of
    //  memset(3), but it's good to know
    //  anyway that there is one. See also
    //  https://stackoverflow.com/q/13720428/20276305
    memset(buffer, '\0', input_size + 1);
    ssize_t bytes_read_count = -1;
    ssize_t bytes_written_count = -1;

    // Reading
    bytes_read_count = read(STDIN_FILENO,
                            buffer,
                            input_size);
    if (bytes_read_count == -1) {
        // No return value checking (and also below). It
        //  would make little sense here since we exit the
        //  function directly after write(2), no matter if
        //  write(2) succeeded or not
        write(STDERR_FILENO, "Error1\n", strlen("Error1\n"));
        return 1;
    }
    // We want to be sure to have a proper string, just in
    //  case we would like to perform more operations on it
    //  one day. So, we need to explicitly end the array
    //  with '\0'. We need to do it regardless of the earlier
    //  memset(3) call because the user might input more
    //  than input_size, so all the '\0' would be
    //  overwritten
    buffer[input_size] = '\0';

    // Writing
    bytes_written_count = write(STDOUT_FILENO,
                                buffer,
                                bytes_read_count);
    if (bytes_written_count == -1) {
        write(STDERR_FILENO, "Error2\n", strlen("Error2\n"));
        return 1;
    }

    return 0;
}