How can I detect error in ioctl I2C_SLAVE call - c

Question

I have been writing some code to access I²C based on the following (which works).
I was attempting to implement something more general, and include error checking.
All the code examples I have seen include similar code to:-
if(ioctl(file, I2C_SLAVE, 0x68) < 0){
perror("Failed to connect to the sensor\n");
return 1;
}
If I use a nonexistent address the code fails, but there is no error.
Can anyone suggest what I am doing wrong?
/** Simple I2C example to read the time from a DS3231 module
* Written by Derek Molloy for the book "Exploring Raspberry Pi" */
#include<stdio.h>
#include<unistd.h> // IB 2022-6-29
#include<fcntl.h>
#include<sys/ioctl.h>
#include<linux/i2c.h>
#include<linux/i2c-dev.h>
#define BUFFER_SIZE 19
// the time is in the registers in decimal form
int bcdToDec(char b) { return (b/16)*10 + (b%16); }
int main(){
int file;
printf("Starting the DS3231 test application\n");
if((file=open("/dev/i2c-1", O_RDWR)) < 0){
perror("failed to open the bus\n");
return 1;
}
if(ioctl(file, I2C_SLAVE, 0x68) < 0){
perror("Failed to connect to the sensor\n");
return 1;
}
char writeBuffer[1] = {0x00};
if(write(file, writeBuffer, 1)!=1){
perror("Failed to reset the read address\n");
return 1;
}
char buf[BUFFER_SIZE];
if(read(file, buf, BUFFER_SIZE)!=BUFFER_SIZE){
perror("Failed to read in the buffer\n");
return 1;
}
printf("The RTC time is %02d:%02d:%02d\n", bcdToDec(buf[2]),
bcdToDec(buf[1]), bcdToDec(buf[0]));
float temperature = buf[0x11] + ((buf[0x12]>>6)*0.25);
printf("The temperature is %.2f°C\n", temperature);
close(file);
return 0;
}