ifstream:: What is the maximum file size that a ifstream can read

Question

I tried to read a 3GB data file using ifstream and it gives me wrong file size, whereas when I read a 600MB file, it gives me the correct result. In addition to wrong file size, I am also unable to read the entire file using ifstream. Here is the code that I used ``` std::wstring name; name.assign(fileName.begin(), fileName.end()); __stat64 buf; if (_wstat64(name.c_str(), &buf) != 0) std::cout << -1; // error, could use errno to find out more std::cout << " Windows file size : " << buf.st_size << std::endl;; std::ifstream fs(fileName.c_str(), std::ifstream::in | std::ifstream::binary); fs.seekg(0, std::ios_base::end); std::cout << " ifstream file size: " << fs.tellg() << std::endl; ``` The output for 3GB file was ``` Windows file size : 3147046042 ifstream file size: -1147921254 ``` Whereas the output for 600 MB file was ``` Windows file size : 678761111 ifstream file size: 678761111 ``` Just in case, I also tested for 5GB file and 300 MB file, The output for 5GB file was ``` Windows…

Accepted Answer

I think you want to say:

```
std::cout << " ifstream  file size: " << fs.tellg().seekpos() << std::endl;
```

At least that works correctly for a 6GB file I have laying around. But I'm compiling with Visual Studio 2012. And even your original code works fine too on that environment.

So I suspect that this is an bug in the std library on VS 2010 that got fixed in VS 2012. Whether it's a bug in the operator overloading for the pos_type or if that class isn't 64-bit aware is unknown. I'd have to install VS 2010 to validate, but that is likely the problem.

ifstream:: What is the maximum file size that a ifstream can read

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