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When sizeof is applied to the name of an array, the result is the number of bytes required to store the entire array. This is one of the few exceptions to the rule that the name of an array is converted to a pointer to the first element of the array, and is possible just because the actual array size is fixed and known at compile time, when the ...
The sizeof operator on such a struct gives the size of the structure as if the flexible array member were empty. This may include padding added to accommodate the flexible member; the compiler is also free to re-use such padding as part of the array itself.
The last member of a C99 structure type with more than one member may be a flexible array member, which takes the syntactic form of an array with unspecified length. This serves a purpose similar to variable-length arrays, but VLAs cannot appear in type definitions, and unlike VLAs, flexible array members have no defined size.
In computer science, an array is a data structure consisting of a collection of elements (values or variables), of same memory size, each identified by at least one array index or key. An array is stored such that the position of each element can be computed from its index tuple by a mathematical formula.
It should be noted that, since sizeof is a compile-time operation, it is impossible to use sizeof to determine the size of an array if it cannot be evaluated at compile time. That's incorrect since C99 introduces variable-length arrays. In that case, the size of the array can only be evaluated at run-time, and sizeof() will be evaluated at runtime.
One use for such "packed" structures is to conserve memory. For example, a structure containing a single byte (such as a char) and a four-byte integer (such as uint32_t) would require three additional bytes of padding. A large array of such structures would use 37.5% less memory if they are packed, although accessing each structure might take ...
In computer programming, a variable-length array (VLA), also called variable-sized or runtime-sized, is an array data structure whose length is determined at runtime, instead of at compile time. [1] In the language C , the VLA is said to have a variably modified data type that depends on a value (see Dependent type ).
The A::max_size() member function returns the largest number of objects of type T that could be expected to be successfully allocated by an invocation of A::allocate; the value returned is typically A::size_type(-1) / sizeof(T). [14] Also, the A::address member function returns an A::pointer denoting the address of an object, given an A::reference.