RL-FlashFS - File overwrite?

It is very difficult to say - nothing of your program/expectations is really explained, but are you sure about this code

...head_index-1 * (4 *,...

Maybe you are missing brackets here?

Hi Tamir thanks for your reply.

Before I posted here I removed all the particulars of my program and tried on very simple test code. I am fairly confident in the multiplication - nonetheless I just re-tried it with a constant and still the same outcome. I went further and I tried this extremely simple test function:

    FILE * f;
    uint32_t i, j;

    if(f = fopen("tf.txt", "w"))
    {

        for(i = 0; i < 100; i++)
        {
            fputc(65,f);
        }
        fflush(f);
        fclose(f);
    }
    else
    {
        return;
    }

    if(f = fopen("tf.txt", "a"))
    {
        j = 38;
        rewind(f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fseek(f, -1L, SEEK_END);
        fclose(f);
    }
    else
    {
        return; //! \todo some form of error handling?
    }

My expectation for this test function would be to create a file with 100 'A' then overwrite the first 32 bytes with NULL and '&' characters.

Are my expectations incorrect?

The result is a file with 100 'A' characters followed by 4 '&' characters.

What am after is a simple example of overwriting a section of a file (using the RL-FlashFS lib). I have tried many combinations all without success in overwriting a section of a file. If I open the file with "a" I can only write to the end of the file.

Thanks

M

What you do seems correct. It could be interesting to test this with a SD card/NAND flash (assuming you use MDK 4.20+). Either way this is worth reporting to our friends at the support.
Did you try to replace the rewind with a fseek? What happens if you execute a fseek, followed by a ftell? does the file pointer even move?

I don't have an SD card or NAND on my hardware but I just tried it on USB and the same thing.

Interestingly enough the following:

...
    if(f = fopen("f:\tf.txt", "a"))
    {
        j = 38;
        printf("\r\n ftell = %d",ftell(f));
        rewind(f);
        printf("\r\n ftell = %d",ftell(f));
        fwrite(&j, sizeof(uint32_t), 1, f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fwrite(&j, sizeof(uint32_t), 1, f);
        fseek(f, -1L, SEEK_END);
        printf("\r\n ftell = %d",ftell(f));
        fclose(f);
    }
...

Outputs:
ftell = 100
ftell = 0
ftell = 115

I guess I will contact support.

Thanks.

M

The reply from support:

**********************
Thank you for using Keil software.

The file pointer only gets used for reading.

The C library does not allow you to open a file in a mode in which you can overwrite a portion of the file, you can either replace the contents of file, or append to it.

If you want to delete part of a file, you need to:

1) make a temporary copy of the file
2) open the original file with mode "w", and the copy in mode "r"
3) copy the portions you want to keep, from the temporary file to the original file
4) close both files
5) delete the temporary file

**********************

I followed up to see if there are any plans to implement other modes (like "r+")...

MDK-ARM Version 4.21
Release Date: 20 Jun, 2011
...
Added: File update mode (r+, w+, a+) support for FAT