更新时间:2022-10-15 17:21:11
In some cases, braces can be elided. This is one of those cases. The outer-most braces for initializing a
and b
are optional. It is syntactically correct either way - but it's clearer to just include them. Clang is just warning you (warning, not error) about this - it's a perfectly valid warning. And as chris, points out, with -Wmissing-braces
, gcc issues the same warning. Ultimately, both compilers accept the code, which is correct; it is, after all, a valid program. That's all that matters.
From [dcl.init.aggr]:
Braces can be elided in an initializer-list as follows. If the initializer-list begins with a left brace, then the succeeding comma-separated list of initializer-clauses initializes the members of a subaggregate; it is erroneous for there to be more initializer-clauses than members. If, however, the initializer-list for a subaggregate does not begin with a left brace, then only enough initializer-clauses from the list are taken to initialize the members of the subaggregate; any remaining initializer-clauses are left to initialize the next member of the aggregate of which the current subaggregate is a member. [ Example:
float y[4][3] = { { 1, 3, 5 }, { 2, 4, 6 }, { 3, 5, 7 }, };
is a completely-braced initialization:
1
,3
, and5
initialize the first row of the arrayy[0]
, namelyy[0][0]
,y[0][1]
, andy[0][2]
. Likewise the next two lines initializey[1]
andy[2]
. The initializer ends early and thereforey[3]
s elements are initialized as if explicitly initialized with an expression of the formfloat()
, that is, are initialized with0.0
. In the following example, braces in the initializer-list are elided; however the initializer-list has the same effect as the completely-braced initializer-list of the above example,float y[4][3] = { 1, 3, 5, 2, 4, 6, 3, 5, 7 };
The initializer for
y
begins with a left brace, but the one fory[0]
does not, therefore three elements from the list are used. Likewise the next three are taken successively fory[1]
andy[2]
. —end example ]