simple problem about fseek()

i have seen some thread discuss about using fseek() to tell the size of the file.

from the msdn, it said it will return -1L if there is error.

i would like to ask how to check if the return value is an error or not?(i think that is not an integer right?)

thank you.

Quote:

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Originally posted by Jasonymk
i have seen some thread discuss about using fseek() to tell the size of the file.

from the msdn, it said it will return -1L if there is error.

i would like to ask how to check if the return value is an error or not?(i think that is not an integer right?)

thank you.

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If it succeeds, it returns zero. Otherwise, you can check errno for specific information about the error.

Code:

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if (fseek(...) != 0)
{
    switch (errno)
    {
        // ...
    }
}

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See here: http://www.mkssoftware.com/docs/man3/fseek.3.asp

or sorry, i should ask about tellg()

in fact my code is:

Code:

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file6.seekg (0, ios::end);
    int file_size = file6.tellg();
    cout << "The file is " << file_size << " bytes." << endl;

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for a file it cant open, the out put will be :

the file is -1 bytes

i have tried to detect the error by if (filesize = -1) but fail, i wonder if the error no is an int or anythng else.

thank you

Code:

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// read a file into memory
#include <iostream>
#include <fstream>
using namespace std;

int main () {
  int length;
  char * buffer;

  ifstream is;
  is.open ("test.txt", ios::binary );

  // get length of file:
  is.seekg (0, ios::end);
  length = is.tellg();
  is.seekg (0, ios::beg);

  // allocate memory:
  buffer = new char [length];

  // read data as a block:
  is.read (buffer,length);

  is.close();

  cout.write (buffer,length);

  return 0;
}

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[1] http://www.cplusplus.com/ref/iostrea...eam/tellg.html

Do you check if the stream is good ?

Code:

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if ( file6.good() ) 
{
  file6.seekg (0, ios::end);
  int file_size = file6.tellg();
  cout << "The file is " << file_size << " bytes." << endl;
  file6.seekg (0, ios::beg);
}
else
{
  cout << "There is a problem with the stream" << endl;
  //do error checking...
}

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