how to find drive free space memory for drive_path Means( C,D,E) code in c

int main(int argc, char *argv[])
{
    long file_size = (long) DEFAULT_FILE_SIZE;
   
  //  printf("%d",sizeof(file_size));
    unsigned char drive_path[256];
    char *opts[256]; 
    FILE *f;
    
    #if (OS == 0)
       fprintf(stderr, "\nError: current OS is not supported.");
       goto exit;
    #endif
    //read input params
    if (get_opts(argc, argv, drive_path) != 0){
       goto exit;
    }
    
    if (can_write(drive_path) != 0){
       fprintf(stderr, "\nError: unable to access/write to drive \"%s\"", drive_path);
       goto exit;                          
    }
   // fseek(&drive_path, 0, SEEK_END);
    BOOL ret; 
    DWORD SectorsPerCluster;
    DWORD BytesPerSector;
    DWORD NumberOfFreeClusters;
    DWORD TotalNumberOfClusters;
    DWORD TotalSpace, TotalSpaceLeft;
    GetFreeSpace(drive_path);
    TotalSpace = BytesPerSector * SectorsPerCluster*TotalNumberOfClusters;

    TotalSpaceLeft=BytesPerSector * SectorsPerCluster * NumberOfFreeClusters;

    printf("  Drive: Total Space=%u bytes Space Left=%u Bytes\n",TotalSpace,TotalSpaceLeft);

   // TotalSpace = (double)diskfree.sectors_per_cluster * (double)diskfree.bytes_per_sector *(double)diskfree.total_clusters / (1024.0*1024.0);


    fprintf(stdout,"\nsize of drive : %d",TotalSpace);
    fprintf(stdout,"\nsize of drive trilok : %s",drive_path);
    char D;
    fprintf(stdout,"\nsize of drive : %d",sizeof(drive_path));
    //wipe free space
    fprintf(stdout, "\nPress ENTER to start wiping free space of drive \"%s\"", drive_path);
    getchar();
    wipe_wrap(drive_path, file_size);
    
    exit:
    
    fprintf(stdout, "\n\nWebsite: https://sourceforge.net/projects/simpledrivewipe/");
	 fprintf(stdout, "\nPress ENTER to quit.");
	 fflush(stdout);
	 
	 getchar();
     ////////////////////////trilok//////////////////////////////
     
     
     
     
        
    return 0;
}