M172 - SIZEOF on dereferenced @STRING does not return size of STRING

[obscuresc]

Hi,

Using the SIZEOF function on a STRING pointer doesn't return the size of the STRING variable, see below.

I am expecting that 'udiStringSize_pointer' would return 6. Note that sStringAlloc5 is of type 'STRING[ 5 ]' while pString is '@STRING'. Is this expected behaviour?

This on EcoStruxure Machine Expert HVAC v1.10.0 on Windows 11 Enterprise 10.0.26200, and on a PLC with BIOS 668.17

Thanks.

[MargheritaM]

Hello,

Use LEN() to get the actual string length.

When SIZEOF() is called with a string, it returns the total size of the string, including the end-of-line character (1 character).

When SIZEOF() is called with a pointer, it returns the size of the pointer itself in bytes.

udiSizeptr1 := SIZEOF(@ptrString1); returns the size of the pointed-to element because the @ operator is interpreted as the dereferenced type of ptrString1, not as the memory address of ptrString1.

In your example, you are requesting the size of the dereferenced type pointed to by pString(@pString)
which corretly returns 1. 

Margherita

 

[obscuresc]

Hi Margherita,

Thanks for getting back to me.

I'm not after the length of the string; only after the size of memory allocated to it.
In your example, on line 9, I want the value of 33 - the same as what is returned on line 3. Why is the value of '1' correct in this case?

Thanks.

[MargheritaM · Accepted solution]

Hello,
it returns 1 because SIZEOF(@ptrString) is calculated during compilation, so it is not always possible to know in advance the size of the string it is pointing to.

Margherita