Get size of very large file in C - Example

Programmazione » Get size large file c linux example
04/05/2018 - 547

How to get the size of a very large file C Linux

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Example of how get the size of very large file in C Linux, with GCC

Working with large files can be a bit tricky under Linux with C due to the lack of documentation. I had some problem with the large file support topic so I decided to provide some examples on working with large files under C Linux, there are no standard functions and for this reason the code portability is not achievable.
In this example below we use the define _LARGEFILE64_SOURCE to enable the large file support on GCC, after that we use the 64 bit versions of the functions fopen -> fopen64, ftell -> ftello64, fseek -> fseeko64, to open the file, get the file pointer, set the file pointer at the end of the file and finally getting the file size.

The function use uses the __off64_t data type that is basically a 8 byte signed integer, could be replaced with long long int in almost all architectures.

//enables the large file support on GCC, must be defined before the includes

#define _LARGEFILE64_SOURCE

#include "stdio.h""

#include "stdlib.h"

#include "string.h"

__off64_t FILE_GetFileSizeFromPath(char *TheFileName);

__off64_t FILE_GetFileSizeFromPath(char *TheFileName)

{

    __off64_t Prev = 0, TheFileSize = 0;

    FILE *TheFilePointer = fopen64(TheFileName, "rb");

    Prev = ftello64(TheFilePointer);

    fseeko64(TheFilePointer, 0, SEEK_END);

    TheFileSize = ftello64(TheFilePointer);

    fseeko64(TheFilePointer, Prev, SEEK_SET);

    fclose(TheFilePointer);

    return TheFileSize;

}

int main(int argc, char** argv) 

{

    __off64_t theSize = 0;

    theSize = FILE_GetFileSizeFromPath("/path/to/theLargeFile");

    printf("\nSize : %lld ", theSize);

    return (EXIT_SUCCESS);

}

Output example:

Size : 10565296876

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