topic Re: MQX 4.2.0 _io_write vs const data in MQX Software Solutions

MQX 4.2.0 _io_write vs const data

rvigneault — Tue, 04 Feb 2020 22:37:41 GMT

Hi,

We are using MQX 4.2.0 and I was quite surprised that _io_write is defined to take a non-const buffer for the data:

extern _mqx_int _io_write(MQX_FILE_PTR, void *, _mqx_int);

I would have expected the second parameter to be something like const void*, furthermore that it is used in the inline definition of fwrite:

#define fwrite(ptr,so,no,f) (_io_write(f,ptr,(so)*(no))/(so))

My question is: is it safe to assume that neither fwrite nor _io_write will modify the pointer that is given to them?

Can there be a problem to remove the const (using a cast) of an array we want to write using fwrite?

Thanks!

Re: MQX 4.2.0 _io_write vs const data

danielchen — Wed, 05 Feb 2020 23:55:18 GMT

Hi Ruby:

Thank you for your feedback. Yes, this is an issue. and it is fixed in MQX v5.

Your can fixed it by yourself.

For MQX v5 we did a full clean up of the code and we made things more consitent and up to date.

Regards

Daniel

Re: MQX 4.2.0 _io_write vs const data

rvigneault — Thu, 06 Feb 2020 14:34:32 GMT

Hi Daniel,

Thank you for your answer.

Just to be clear, the issue here is only that the parameter is not declared as const?

I mean, it is used as const (i.e. not modified) by the _io_write implementation right?

If so, I guess that _strnlen is the same (i.e. the first parameter is not modified and can be considered as const char*). I stumbled upon it yesterday after my question.

Thanks!

Re: MQX 4.2.0 _io_write vs const data

danielchen — Fri, 07 Feb 2020 03:05:59 GMT

Yes, you are right.

Regards

Daniel