Simple C string initialization concept clarification needed

Question

If I have a C string initialization like this:

char a[5]={'a','b','c'};

Is this valid? What's the value of a[3] and a[4]? Is the null character automatically attached to the end of a?

Thanks!

The last two elements should be indeterminate or uninitialized IMO. — Morten Jensen, Feb 27 '14 at 23:35
_If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration._ 6.7.8 Initialization 21 — BLUEPIXY, Feb 28 '14 at 00:20

score 5 · Answer 1 · answered Feb 27 '14 at 23:36

5

They would be initialized to a value of 0. Null is automatically added when you leave some elements uninitialized.

answered Feb 27 '14 at 23:36

user376507

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brokenfoot · Answer 2 · 2014-02-28T22:10:18.893

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It depends on what C std you are following:

If you follow C90 STRICTLY then it forbids you to do it, Thanks BLUEPIXY for the enlightenment
Then, there are certain extensions to these standards which enable you to compile this code without any error, in which case, this is fine.

So, in case of the later, C language takes care by initializing rest to zero .

char a[5] = {}

initializes all indexes to zero.

edited Feb 28 '14 at 22:10

answered Feb 27 '14 at 23:38

brokenfoot

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I think when somebody down votes, he should convey the reason for doing so. – brokenfoot Feb 28 '14 at 00:01
ISO C forbids empty initializer braces. – BLUEPIXY Feb 28 '14 at 00:26
No, ISO C99 allows it: http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html Also, the same has been answered here at SO: http://stackoverflow.com/questions/201101/how-to-initialize-an-array-in-c – brokenfoot Feb 28 '14 at 00:34
you try `gcc prog.c -std=c99 -pedantic` – BLUEPIXY Feb 28 '14 at 00:45
You seem to be creating a program that takes a long time really. – BLUEPIXY Feb 28 '14 at 08:20
Oh..You shared the link to the ideone code.. remember? I trust you :) – brokenfoot Feb 28 '14 at 18:54
How is that so?? Please look at the top ans, says the exact same thing ! It has 5 votes, are you challenging those 5 voters ? – brokenfoot Feb 28 '14 at 22:41

score 0 · Answer 3 · answered Feb 27 '14 at 23:39

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If called within a function a[3] and a[4] will be uninitiallised. That is to say, they will be whatever happens to be sitting in memory at the time.

If declared outside a function, a[3] and a[4] will be set to 0.

answered Feb 27 '14 at 23:39

DXsmiley

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This is not true. Missing indexes in initializer are treated as zero. – user3125367 Feb 28 '14 at 00:00

score -1 · Answer 4 · answered Feb 27 '14 at 23:37

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Depending on the implementation I believe that the last elements of an array will be either completely random or just equivalents of 0's or even something else, but besides of that array will get initialized just fine.

answered Feb 27 '14 at 23:37

Peter Nimroot

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Simple C string initialization concept clarification needed

4 Answers4