Is there a possibility to convert array of double to char *?

Question

I am writing a program which has to create a file, map it to the memory and then write two-dimensional array of doubles to it. I encounter a problem when I look into the file. It is full of not expected values. I guess, this problem is related to casting, but can't come up with solution. So, the question is, how to convert array of doubles to char *? Hope someone can give me a clue to solve this problem.

int main(int argc, char **argv)
{
    HANDLE plik, mappedFile;
    char  *poi;
    LPCWSTR fileName = L"plik.txt";
    double tab[8][12];
    createMatrix(tab); // here I fill the array with values

    // creating file
     // mapping the file

   poi = (char *)MapViewOfFile(
    mappedFile,
    FILE_MAP_ALL_ACCESS,
    0,
    0,
    0);

if (!poi)
{
    puts("Can't allocate Memory!");
    abort();
}

memcpy(poi,tab,96*sizeof(double));

UnmapViewOfFile((void*)poi);
CloseHandle(mappedFile);
CloseHandle(plik);
getchar();
return 0;
}

Answer 1

I think your code is working, the file contains the double numbers, but remember that it's a binary format with floating point format, so a text editor will just show it as some junk. Try a hex editor, and check the double format. Or try to read it back.

The major problem with your approach is that it's not cross platform, a machine with different endianness wouldn't be able to properly read it (this may or may not be a problem for you).

What you want is serialization . The simplest version would just print the numbers in the file (with some user-defined limited precision) - eg with sprintf ..

Answer 2

Are you looking for something like this:

char* poi = new char[8*12*sizeof(double)];
int index = 0;

for(int i = 0; i < 8; i++)
{
    for(int j = 0; j < 12; j++)
    {
        *(double*)(poi + index) = tab[i][j];
        index+=sizeof(double);
    }
}

Answer 3

I suggest you to replace file mapping with simple WriteFile function. It can be faster for many applications.

WriteFile(plic, tab, sizeof(tab), 0, 0);

will serialize your data accurately and quickly.