Redundant C variable initialization for redundant reasons.

The top article on this site for the past 5 or so years has been a simple C tidbit about splitting 16-bit values in to 8-bit values. Because of this, I continue to drop small C things here in case they might help when someone stumbles upon them.

Today, I’ll mention some redundant, useless code I always try to add.,,

I seem to recall that older specifications for the C programming language did not guarantee variables would be initialized to 0. I am not even sure if the current specification defines this, since one of the compilers I use at work has a specific proprietary override to enable this behavior.

You might find that this code prints non-zero on certain systems:

int i;

printf ("i = %d\n", i);

Likewise, trying to print a buffer that has not been initialized might produce non-empty data:

char message[32];

printf ("Message: '%s'\n", message);

Because of this, it’s a good habit to always initialize variables with at least something:

int i=0;

char message[42];
memset (message, 0x0, sizeof(message));

Likewise, when setting variables in code, it is also a good idea to always set an expected result and NOT rely on any previous initialization. For example:

int result = -1;

if (something == 1)
    result = 10;
else if (something == 2)
    result = 42;
    result = -1;

Above, you can clearly see that in the case none of the something values are met, it defaults to setting “result” to the same value it was just initialized to.

This is just redundant, wasteful code.

And you should always do it, unless you absolutely positively need those extra bytes of code space.

It is quite possible that at some point this code could be copy/pasted elsewhere, without the initialization. On first compile, the coder sees the undeclared “result” and just adds “int result;” at the top of the function. If the final else with “result = -1;” wasn’t there, the results could be unexpected.

The reverse of this is also true. If you know you are coding so you ALWAYS return a value and never rely on initialized defaults, it would be safe to just do “int result;” at the top of this code. But, many modern compilers will warn you of “possibly initialized variables.”

Because of this, I always try to initialize any variable (sometimes to a value I know it won’t ever use, to aid in debugging — “why did I suddenly get 42 back from this function? Oh, my code must not be running…”).

And I always try to have a redundant default “else” or whatever to set it, instead of relying on “always try.”

Maybe two “always tries” make a “did”?

Until next time…

2 thoughts on “Redundant C variable initialization for redundant reasons.

  1. MiaM

    A decent optimizer will ensure that your result = -1 duplication won’t generate any extra code anyways, so there isn’t even any increase in program size by doing this.

    Sure, some embedded systems C compilers might not be smart enough…

    1. Allen Huffman Post author

      Those compilers are my world :) But I do like the idea of writing it out full code that only has a negative impact on poor compilers.


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