Question

I have two question :

• I have a data on binary file. I want read first 8 bytes to signed long int by using read function but I could not . Do you know how can I do that ?

• How can directly read a block of data to string ?
  Can I read like as shown in
  ex :

   ifstream is;
   is.open ("test.txt", ios::binary );
  
   string str ;
   is. read ( str.c_str, 40 ) ; // 40 bytes should be read
  

Answer 1

I want read first 8 bytes to signed long int by using read function but I could not . Do you know how can I do that?

Don’t assume long is wide enough, it often isn’t. long long is guaranteed to be at least 8 bytes wide, though:

long long x;
is.read(static_cast<char *>(&x), 8);

Mind you, this is still incredibly non-portable due to varying integer sizes and endiannesses.

As for your second question, try

char buf[41];
is.read(buf, 40);
// check for errors
buf[40] = '\0';

std::string str(buf);

or, safer

char buf[41];
is.get(buf, sizeof(buf), '\0');
std::string str(buf);