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It's really unclear to me why anyone would name a particular form of initialization "value initialization". It sounds as though it's initializing the object by giving it a value... but that's what initialization does in general, and the name doesn't tell you anything about which value it's going to use for the initialization.
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Again, in your case this just means that all members are value-initialized. Value initialization for fundamental types means zero-initialization, which in turn means that the variables are initialized to zero (which all fundamental types have). For objects of class type, both default- and value-initialization invoke the default constructor.
The way to value-initialize a named variable before C++11 was T object = T();, which value-initializes a temporary and then copy-initializes the object: most compilers optimize out the copy in this case. References cannot be value-initialized. As described in functional cast, the syntax T() (1) is prohibited for arrays, while T{} (5) is allowed.
The effects of value initialization are: 1) if T is a class type with at least one user-provided constructor of any kind, the default constructor is called; 2) if T is a non-union class type without any user-provided constructors, every non-static data member and base-class component of T is value-initialized;
A declared variable can be Zero Initialized, Value Initialized or Default Initialized. The C++03 Standard 8.5/5 aptly defines each: To zero-initialize an object of type T means: — if T is a reference type, no initialization is performed.
The Boost value_init write-up provide a rather detailed history of value initialization it ended up in the standard from defect report 178: More on value-initialization and it seems like the term originated from defect report 35: Definition of default-initialization. Although none of these documents really provide a proper origin for the term it does provide some good ideas, it says:
The first Technical Corrigendum for the C++ Standard (TC1), whose draft was released to the public in November 2001, introduced Core Issue 178 (among many other issues, of course).
That issue introduced the new concept of value-initialization (it also fixed the wording for zero-initialization). Informally, value-initialization is similar to default-initialization with the exception that in some cases non-static data members and base class sub-objects are also value-initialized. The difference is that an object that is value-initialized won't have (or at least is less likely to have) indeterminate values for data members and base class sub-objects; unlike the case of an object default constructed. (see Core Issue 178 for a normative description).
In order to specify value-initialization of an object we need to use the empty-set initializer: ().
and value initialization is less likely to leave an object with an indeterminate value versus default-initalization.
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