Thread: what am I doing wrong with this fseek?

From MinGW-users - ftello64

I suggest trying ftello64 and fseeko64; I have never even heard of them before.
But, it is worth trying.

Tim S.

Originally Posted by Salem

When writing portable code, you should look to create your own wrapper functions around the variable functionality.
Eg.

Code:

#ifdef WIN32
// Windows
long long myGetFileSize ( const char *filename ) {
    long long result = -1;
    LARGE_INTEGER answer;
    HANDLE hFile = CreateFile( filename, ... );
    if ( GetFileSizeEx(hFile,&answer) ) {
        result = (long long)answer;
    }
    CloseHandle(hFile);
    return result;
}
#else
// assume POSIX
long long myGetFileSize ( const char *filename ) {
    long long result = -1;
    int fd = open(filename,O_RDONLY);
    if ( fd >= 0 ) {
        result = lseek64(fd, 0, SEEK_END);
    }
    close(fd);
    return result;
}
#endif

In a larger project, you'll end up with several of these, so it make sense to have
- porting.h containing all the prototypes
- porting_win32.c containing all the win32 stuff
- porting_posix.c containing all the posix stuff

So you compile all your code, and whichever of the porting.... files makes sense for the platform you're using.

Your code doesn't compile. I just need a working example so that I can understand what is going on with it, substitute vars and play around with it untill I am sure that I know it.
POSIX from what I have searched on the web does not appear to have any working examples either just like the Win32.

> Your code doesn't compile. I just need a working example so that I can understand what is going on with it
You'll learn more by making what I've posted work.

> substitute vars and play around with it untill I am sure that I know it.
Yes, the "painting by numbers" approach.
All this will teach you is how to solve problems which are very similar to problems you've already seen.

> I am hoping to write code that can be compiled for Windows, Mac OSX, and Linux
If you seriously want to get to this point in any reasonable amount of time, you need to pick up the pace of learning and trying things for yourself.
Waiting for other people to give you fully working code just so you can tinker with it a line at a time just won't get you to where you're aspiring to be.

I have tried google and dogpile searching for information about how to do this, I have concluded that there is very little information to be had about these processes.
The best I could come up with was:

Code:

#include <stdio.h>
FILE = *fp;
main()


{
    unsigned long long filesize;
    char[] s= "g:\\Mess.m2ts"
    fp = &s;
    open64("fp, "rb");
    fpos_t file_pos;
    filesize =ftell (fsetpos SEEK_END);
    printf (" the file size is : %ull",filesize);
    return 0;
}

but I can't get it to work,not even compile. how do I define the _LARGE_FILE_API macro?
Salem I just don't understand your example

This was more or less OK (as a valid C program)

Code:

FILE *f = fopen("g:\\Mess.m2ts", "rb");
if (f)
   fseek(f, 0ull, SEEK_END);
   size = ftell(f);
   fclose(f);
   printf ("size is : %ull", size);

This on the other hand misses the target by a country mile.

Code:

FILE = *fp;
main()
{
    unsigned long long filesize;
    char[] s= "g:\\Mess.m2ts"
    fp = &s;
    open64("fp, "rb");
    fpos_t file_pos;
    filesize =ftell (fsetpos SEEK_END);
    printf (" the file size is : %ull",filesize);
    return 0;
}

This isn't code, this is just random key presses.

I repeat my previous assertion.
Learn standard C before venturing out into the world of OS specific API calls.

These are NOT the same characters: 0, O, and o !!

I am giving up on helping you; you seem to not understand simple C syntax.
You need to walk before you try to run.

Tim S.

Salem, your code does not compile, the IDE(Code::Blocks) keeps saying that LARGE_INTEGER is an unknown type and so is HANDLE and that #ifdef is unterminated.
Is there something that I should #include? Or is there something wrong with my compiler(GCC)?
I am focusing on the Windows part of your program only.
Thanks

Code:

#include <stdio.h>

// Code from http://www.daniweb.com/software-development/c/code/238780/fseeko64-and-ftello64-for-deal-with-large-files-eg.-file-dimension
// Edited for CB MinGW GCC

int main ()
{

    FILE * pFile;

    unsigned long long file_dim = 0;
    char file_name[260] = "";

/////////////////////////////////////////////////////////

    printf("ENTER [path] file name.ext:\n");
    gets(file_name);

    pFile = fopen (file_name,"rb");

    if (pFile==NULL)
        perror ("Error opening file");
    else
    {
        fseeko64 (pFile, 0, SEEK_END);
        file_dim = ftello64 (pFile);
        fclose (pFile);
        printf ("File:\n%s\ncontains %I64d bytes:\n", file_name, file_dim);
    }
    return 0;
}

Tim S.

Salem example was likely using MS Visual C or C++; My posted example used MinGW GCC C code or maybe Borland C code.

FYI: When doing MS Visual C or C++ example code always include "windows.h" unless told to NOT do so.

Tim S.

Thanks for informing me. I thought that visual C after version 6 uses .NET
I might look into trying it since it does native code, I could use the multi thread options I think but it is not free which will probably mean that I will hold off on trying it for a while