seekUserFile MDot API fails, when fetching last byte in the file.

[Ajay K]

I have a requirement to read the last byte from a custom file we store in the flash using the MDot File Api.

Here is a log information, when attempting to read the last byte of the file.

[TRACE] File Name: DeviceInfoBkp.dat, Size: 162 bytes.
[ERROR] SPIFFS_lseek failed -10003

This is the version of the production mbed mdot library we are using.
MDOT Library version: 3.1.0 and MBED OS Version: 5.7.7.

Also here is the code that we are using

uint8_t nChannelPlan = 0;
    
//check and see if the bkp file exists, if so read the file and read the last //byte of the file.
mDot::mdot_file file = m_pDot->openUserFile(DeviceInfoBkpFileName, mDot::FM_RDONLY);

//check if the file exists.    
if(file.fd >= 0 && file.size > 0) {
     if(m_pDot->seekUserFile(file, 1, SEEK_END)) {
         if(m_pDot->readUserFile(file, &nChannelPlan , sizeof(uint8_t))){
            logDebug("Channel Plan: %u", nChannelPlan);
         }
     }
}

m_pDot->closeUserFile(file);

Thanks,
Ajay.

[Jason Reiss]

Did you try to seek using offset -1 from the end to get the last byte.

https://fresh2refresh.com/c-programming/c-file-handling/fseek-seek_set-seek_cur-seek_end-functions-c/

[Ajay K]

Hi Jason,

Thanks for taking the time to respond, isn’t size_t below an unsigned integer type? Can I pass a negative number?

bool seekUserFile(mDot::mdot_file& file, size_t offset, int whence);

Thanks,
Ajay

[Jason Reiss]

It should be signed, that will be an issue for using SEEK_END. I will have to change that in the future.

Can you use the size to seek from the beginning?

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