Finding file size with file input/output operations

[sedulous]

Hey people,

I want to be able to find file size using file input/output operations "open()" function.

Typically, to open a file, we use for example: ifstream f ("/home/arjun/test_file.txt");

But, I want the complete file name ("/home/arjun/test_file.txt") to be stored in a variable so that any file can be opened and read from. I can then use other file handling operations to find its size.

Right now, if I am using a string variable to store the file name and then use it in the "open()" function, it's giving me errors.
Can it be done? If yes, how?

Thanks

[Peter87]

Upgrade your compiler or use the c_str() member function to get a C-string from a std::string.

std::string filename = "/home/arjun/test_file.txt";
std::ifstream f(filename.c_str());

[sedulous]

Thanks a lot Peter for your help. I tried out using c_str() function mentioned by you and it works.
What has upgrading my computer got to do with this? My machine is a recent product and is not old though.

[TwilightSpectre]

Upgrading your compiler, not your computer - as in, the thing you build your program with. If you are using Code::Blocks or GCC or Clang or something along those lines, your compiler could well be recent enough, you just need to pass -std=c++11 to the command line (or find the option for C++11 compliance in the build settings). This is because before C++11, std::fstream did not have a constructor taking a std::string, only a const char*.

[sedulous]

Hey NT3, my bad for misreading compiler. Thanks for this new option for 'g++'. It worked!

[kbw]

Finding file size with file input/output operations

Don't. Check the file's metadata instead.

Opening a file is among one of the most expensive things you can ask an OS to do, so don't do it lightly.