Write to ESC/POS protocol to BLE printer

printer_helloworld_with_style.m

- (IBAction)printHelloWorld:(id)sender {
    
    NSString * str = @"Hello World\n\r";
    
    NSString *command = @"1B2100";
    
    NSMutableData *commandToSend= [[NSMutableData alloc] init];
    unsigned char whole_byte;
    char byte_chars[3] = {'\0','\0','\0'};
    int i;
    for (i=0; i < [command length]/2; i++) {
        byte_chars[0] = [command characterAtIndex:i*2];
        byte_chars[1] = [command characterAtIndex:i*2+1];
        whole_byte = strtol(byte_chars, NULL, 16);
        [commandToSend appendBytes:&whole_byte length:1];
    }
    NSData* data = [str dataUsingEncoding:NSUTF8StringEncoding];
    [commandToSend appendData:data];
    
    [self.printerPeripheral writeValue:commandToSend forCharacteristic:self.writeCharacteristic type:CBCharacteristicWriteWithoutResponse];
}