C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
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Section 26:
[26.8] When initializing non-static data members of built-in / intrinsic / primitive types, should I use the "initialization list" or assignment?

For symmetry, it is usually best to initialize all non-static data members in the constructor's "initialization list," even those that are of a built-in / intrinsic / primitive type. The FAQ shows you why and how.