Re: [EE] Ideas about improving safety in C language

On Tue, 15 Apr 2025, Isaac Marino Bavaresco wrote:

> Hi folks,
>
> I was thinking about the current discussion about C/C++ language safety, 
> and I recalled an old idea I had long ago about creating a new string 
> format and library.
>
> It could be possible for one person alone to implement and use it 
> privately, but of course it would be even better if it becomes a 
> standard, perhaps with support from the compilers.
>
> I don't know whether something similar was already suggested or is being 
> used, but I would like to know your opinion about it.
>

Hi Isaac,

Really sorry to rain on your parade but nothing you do will ever make 
C/C++ strings safe.

The problem is that no mater how you craft your libraries, the complier is 
not aware of the fundamental properties of a string so a pointer to a 
string will never feedback info to the compiler and the compiler will 
therefore never be able to compensate for pointer misuse.

Consider two fundamental common operations on a string:
(1) appending data to a string
(2) scanning a string character by character

In (1) it is often necessary to increase the size of the string. This 
involves allocating a new memory area on the heap (often using realloc). 
This sometimes causes old pointers to be invalidated - they point to 
sections of the heap which have been freed while the grown string has been 
copied to a new section of the heap.

In (2) a pointer is slowly moved along a string while each character of 
the string is processed. Maybe a specific character is being search for. 
What happens if the string suddenly changes size or is moved to a new heap 
position? The pointer will become rouge and could cause all kinds of 
damage. We get the argument that a string cannot suddenly move. Actually 
this is a VERY real danger. What happens if two of more threads access the 
same string at the same time? Can't happen? What about the main line and 
an interrupt handler? What about a function calling another function with 
a string it is actualy using? The child function modifies the string, the 
string gets realloced and the parent function is now (sometimes) left 
procesing a freed section of memory.

The only way you are ever going to have safe strings is if the compiler 
can track their use and generate extra code depending on how it sees they 
are being used.

Just my 2 cents worth.

Friendly Regards
Sergio Masci