Sets the initial value of an object to zero.

[edit]Syntax

Note that this is not the syntax for zero-initialization, which does not have a dedicated syntax in the language. These are examples of other types of initializations, which might perform zero-initialization.

[edit]Explanation

Zero-initialization is performed in the following situations:

The effects of zero-initialization are:

• IfT is ascalar type, the object is initialized to the value obtained byexplicitly converting the integer literal​0​ (zero) toT.
• IfT is a non-union class type:

• allpadding bits are initialized to zero bits,
• each non-staticdata member is zero-initialized,
• each non-virtual base classsubobject is zero-initialized, and
• if the object is not a base class subobject, eachvirtual base class subobject is zero-initialized.

• IfT is a union type:

• all padding bits are initialized to zero bits, and
• the object’s first non-static named data member is zero-initialized.

• IfT is array type, each element is zero-initialized.
• IfT is reference type, nothing is done.

[edit]Notes

As described innon-local initialization, static and thread-local(since C++11) variables that aren't constant-initialized are zero-initialized before any other initialization takes place. If the definition of a non-class non-local variable has no initializer, then default initialization does nothing, leaving the result of the earlier zero-initialization unmodified.

A zero-initialized pointer is the null pointer value of its type, even if the value of the null pointer is not integral zero.

[edit]Example

#include <iostream>#include <string> struct A{int a, b, c;}; double f[3];// zero-initialized to three 0.0's int* p;// zero-initialized to null pointer value// (even if the value is not integral 0) std::string s;// zero-initialized to indeterminate value, then// default-initialized to "" by the std::string default constructor int main(int argc,char*[]){    delete p;// safe to delete a null pointer staticint n= argc;// zero-initialized to 0 then copy-initialized to argcstd::cout<<"n = "<< n<<'\n';     A a= A();// the effect is same as: A a{}; or A a = {};std::cout<<"a = {"<< a.a<<' '<< a.b<<' '<< a.c<<"}\n";}

n = 1a = {0 0 0}

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

• constructor
• copy assignment
• default constructor
• initialization
  • aggregate initialization
  • constant initialization
  • copy initialization
  • default initialization
  • direct initialization
  • list initialization
  • value initialization
• move assignment
• new

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