Question

In C one can write (disregarding any checks on purpose)

const int bytes = 10;
FILE* fp = fopen("file.bin","rb");
char* buffer = malloc(bytes);
int n = fread( buffer, sizeof(char), bytes, fp );
...

and n will contain the actual number of bytes read which could be smaller than 10 (bytes).

how do you do the equivalent in C++ ?

I have this but it seems suboptimal (feels so verbose and does extra I/O), is there a better way?

  const int bytes = 10;
  ifstream char> pf("file.bin",ios::binary);
  vector<char> v(bytes);

  pf.read(&v[0],bytes);
  if ( pf.fail() )
  {
    pf.clear();
    pf.seekg(0,SEEK_END);
    n = static_cast<int>(pf.tellg());
  }
  else
  {
    n = bytes;
  }

  ...

Answer 1

Call the gcount member function directly after your call to read.

pf.read(&v[0],bytes);
int n = pf.gcount();