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Is the comma (,) a sequence point in std::initializer_list?

example: is this UB or not:

#include <vector> int main() { auto nums = [] { static unsigned x = 2; return ( x++ % 2 ) + 1; }; std::vector< int > v{ nums(), nums(), nums(), nums(), nums() }; // not sure if this is different: (note the additional brackets) // std::vector< int > v({ nums(), nums(), nums(), nums(), nums() }); for( auto i : v ) { std::cout << i; } return 0; }
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    There are no "sequence points" any more in C++11. However, the order of evaluation is guaranteed and it is indeed ordered, but I'll search for a duplicate first before answering. Commented Nov 28, 2013 at 12:28
  • @DyP - thanks. I didn't find duplicate, although I'm pretty sure I've seen similar question.. I'm almost sure, the order is guaranteed, but not 100%. Commented Nov 28, 2013 at 12:29
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    [dcl.init.list]/4 "That is, every value computation and side effect associated with a given initializer-clause is sequenced before every value computation and side effect associated with any initializer-clause that follows it in the comma-separated list of the initializer-list." Commented Nov 28, 2013 at 12:30
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    @Kiril: Yeah, it's a notion of "sequenced-before" and "sequenced-after", now. Commented Nov 28, 2013 at 12:32
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    Also search for the [c++11] tag ;) To answer the question in the code comment: No, it's not different. It's list-initialization in both cases, so the same rules apply wrt sequencing. The second one could have a different meaning (in a general case), but is has the same meaning here: Call the initializer_list constructor of vector with an initializer_list constructed via list-initialization. Commented Nov 28, 2013 at 12:39

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According to C++11 § 8.5.4 [dcl.init.list] paragraph 4:

4 Within the initializer-list of a braced-init-list, the initializer-clauses, including any that result from pack expansions (14.5.3), are evaluated in the order in which they appear. That is, every value computation and side effect associated with a given initializer-clause is sequenced before every value computation and side effect associated with any initializer-clause that follows it in the comma-separated list of the initializer-list.

As far as I know GCC 4.8.1 has a bug relative to evaluation of initializers. I described it here

http://cpp.forum24.ru/?1-3-0-00000063-000-0-0-1378892425

Though the text is written in Russion but it can be simply translated in English by using for example google translate.

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