what is the use of "-" while printing hex using printf

Question

I was going through one of the example codes of esp-idf and I found out that they were using the following syntax to print hex number.

ESP_LOGE(TAG, "mbedtls_ssl_handshake returned -0x%x", -ret);

The ESP_LOGE() syntax just prints the output to the console through UART. I am not understanding what is the use of "-" in it. Can anyone help me why they have used "-" in it? The code which I was referring to is here. When I tried a simple example to print the same hex using CI was getting different output when I used -ret and when I replaced it with ret .

Answer 1

%x will print hex representation of the unsigned number.

example:

int x = -0x45;
printf("%x\n", x);

https://godbolt.org/z/j3r3nv1s1

It will print (assuming two's complement 32 bits integers) ffffffbb which is not you want to see if you intended to print a negative hex number. You need to convert it to a positive number and simply add - to the format string. REMEMBER in two complement's system it will not work for INT_MIN number and it will invoke an Undefined Behaviour.

int x = -0x45;
printf("-%x\n", -x);  //you can also use abs(x)

It will output -45. https://godbolt.org/z/ePbdrcqb5

You may add 0x as well to show that number is in hex format.

printf("-0x%x\n", -x);

https://godbolt.org/z/saqf8c9dY