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c++c++11auto

C++11 auto variable : float array vs auto

Size of float array declared is suing auto is different than actual size. why is it so ??

For e.g:

declaration: 

float duto[] = {2.2222f,2.223f,34.5f,1.0f,9.0f};
auto dutot = {2.2222f,2.223f,34.5f,1.0f,9.0f};

Size print:

std::cout << " float array size v: " << sizeof(duto)<<std::endl;
std::cout << " auto v: " << sizeof(dutot)<<std::endl;

Output: 

float array size v: 20
auto v: 16
Solution

  • auto dutot = {2.2222f,2.223f,34.5f,1.0f,9.0f};

    auto here is actually deduced as initializer_list<float>. so you are printing the size of initializer_list<float>.

    I just took a look at initializer_list implementation in g++ 4.8.2 on my ubuntu 14.04. it contains two members _M_array and _M_len. _M_array is a pointer, _M_len's type is size_t. So I guess your machine is 64bit. since pointer and size_t are usually 8 bytes on 64bit platform.