How to suppress sprintf() warning 'directive writing between 1 and 11 bytes into a region of size 6 '

with

sprintf(tag, "Literal - %d", literal); 

since your buffer is 16 bytes, and the prefix is 10 bytes, that leaves 5 bytes to write the string representation of literal.

Since int is probably 32 bit on your system, it ranges up to 2147483647 and negative-wise -2147483648 (11 characters), the compiler warns you (since it was able to compute all the sizes)

Now since you know that the range cannot be outside 0-255, just reduce literal size by, for instance, declaring it as unsigned short (short can be 6 bytes long as a string: -32768 as chux noted in comments) so you have leeway for your value.

unsigned short literal = 123;
sprintf(tag, "Literal - %hu", literal); 

(you could use unsigned char which ranges exactly from 0 to 255, using %hhu format specifier)

or just cast when printing:

sprintf(tag, "Literal - %hu", (unsigned short)literal); 

(%u probably works too, but depends on how smart the compiler is: is it analysing just the format or the size of variable args?)

Let's not forget the most obvious solution now that we know why the warning occurs: let's define the array with a large enough size.

char tag[25];  // 21 would have been okay

should do it. Shaving it too close isn't generally a good idea, unless you're running out of ressources.

This warning is valid because tag is not large enough to hold all possible values of the string to be constructed.

An integer, assuming 32 bits, needs up to 11 characters to store its string representation. There are 10 characters written to tag before the integer value, so there are 6 bytes left to write other data. That's what the warning is telling you.

Since literal has a range of 0 to 255, you can cast the value to unsigned char and use %hhu for the format specifier, which states that the argument is an unsigned char.

In general sprintf is considered unsafe, as it doesn't check the bounds of its ouput array. You should consider using snprintf instead when writing into a fixed size buffer:

snprintf(tag, sizeof(tag), "Literal - %d", literal);