what type of cast should I use here?

Question

I have this code:

m_file.seekg(0, std::ios_base::end);
int fileSize = (int)(m_file.tellg());
m_file.seekg(0, std::ios_base::beg);
m_fileContent.resize(fileSize);
m_file.read(m_fileContent.data(), fileSize);

the idea is to read the content of a binary file into a vector. This code is compiled and run well, but I am not sure this line is correct in a c++ environment?

 int fileSize = (int)(m_file.tellg());

Am I using the correct cast? It is ac style cast and not a c++ one. I tried this cast but it generate compiler error:

 int fileSize = reinterpret_cast<int>(m_file.tellg());

but I am getting this error:

'reinterpret_cast' : cannot convert from 'std::fpos<_Mbstatet>' to 'int'    

what is the best way to cast value types to each other? Should I use C style cast or C++ style cast?

Answer 1

您根本不需要演员，而是使用

size_t fileSize = file.tellg();

Answer 2

You shouldn't be casting at all, but rather (assuming C++11) using auto , ie:

auto fileSize = m_file.tellg();

It will ensure that you don't use the wrong type and avoid implicit casts that may end up in losing info (like casting from a larger type to a smaller one). Plus you don't have to bother with the actual type (which can be cumbersome to type, and that you may get wrong).

Answer 3

Before C++11 I believe the correct thing to do is this:

std::fstream::pos_type fileSize = m_file.tellg();

If you have C++11 then you can do this:

auto fileSize = m_file.tellg();