Hello,
I'm wondering if it's possible, and if so if someone has an example, to overwrite a portion of a file using the RL-FlashFS library.
Basically I have a working setup and I have a small file system on NOR flash. I have a fixed size file and I want to overwrite a middle section of this file.
If I try something like:
if(f = fopen("my_test_file", "a")) { int j = 38; rewind(f); fseek(f, header.head_index-1 * (4 * sizeof(uint32_t)), SEEK_SET); 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); }
The rewind doesn't seem to do anything and it just appends the 4 ints to the end of the file.
Any ideas? Am I doing something wrong?
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.
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