What does char c[2] = { [1] = 7 }; do?

Question

I am reading Bruce Dawson's article on porting Chromium to VC 2015, and he encountered some C code that I don't understand.

The code is:

char c[2] = { [1] = 7 };

Bruce's only comment on it is: "I am not familiar with the array initialization syntax used - I assume it is some C-only construct." So what does this syntax actually mean?

Adam B · Accepted Answer · 2016-03-25T17:03:15.893

12

C99 allows you to specify the elements of the array in any order (this appears to be called "Designated Initializers" if you're searching for it). So this construct is assigning 7 to the second element of c.

This expression is equivalent to char c[2] = {0, 7}; which does not save space for such a short initializer but is very helpful for larger sparse arrays.

See this page for more information: https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html

edited Mar 25 '16 at 17:03

answered Mar 25 '16 at 16:43

Adam B

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It's equivalent to `char c[2] = {0, 7};` here but designated initializer is very convenient in the cases long arrays and structures. – P.P Mar 25 '16 at 16:50
That is another easy way to visualize, it. Added to the answer. – Adam B Mar 25 '16 at 17:04

Mukesh · Answer 2 · 2016-03-25T16:59:07.387

2

Its meaning would be

char c[2]={ 0, 7 }

OR you can say

char c[2];
c[0]=0;
c[1]=7;

edited Mar 25 '16 at 16:59

answered Mar 25 '16 at 16:50

Mukesh

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Why `NULL`, that's a null ***pointer*** constant?! You want to use `0` or `'\0'` to initialise a `char`. – alk Mar 25 '16 at 16:54
oh sry i meant 0x0 its nt NULL – Mukesh Mar 25 '16 at 16:58
Your second example is not an initializer but run-time statements. – Paul Ogilvie Mar 25 '16 at 17:05
it was to explain what it does – Mukesh Mar 25 '16 at 17:09

What does char c[2] = { [1] = 7 }; do?

2 Answers2