About Representation of C data types

Garvin Tan said:

I saw a table C table types

Where did you see it?

Garvin Tan said:

What did items in the representation mean

Didn't the context of the table explain that?

Whithout knowing the context, it's impossible to know exactly what it was intended to mean or convey!

At a guess, it looks to me like a table of how a debugger will display various data types;  presumably, these are defaults - and can be changed if required.

Garvin Tan said:

the different between them

Again, didn't the context of the table explain that?

Any basic textbook - or a bit of googling - should explain what "ASCII", "2's complement", "Binary", and "IEEE" formats mean...

Garvin Tan said:

In my opinin

It's not your opinion that counts - it's whatever is defined by the particular tool or device. You must study its documentation for details...

Garvin Tan said:

variables are binary stored in memory

Although it is true that the memory hardware just stores 1s and 0s^[1] (ie, binary), those 1s and 0s can be used in many different ways to represent many different types of data; eg,

• To represent printable characters - commonly using ASCII encoding;
   
• To represent unsigned integral numeric values (values never less than zero);
   
• To represent signed integral numeric values (values above, below, or equal to zero);
   
• To represent non-integral values (with a fractional part);
   
• To represent a memory address;
   
• As raw, binary bit patterns;
   
• etc, etc,...

[1] Note: the memory hardware itself doesn't even know about "1" or "0" - it just knows about voltage levels. The use of "1" and "0" is just a convenient representation...

Petr Kras said:

What does it mean IEEE 33-bit (for double) and IEEE 34-bit (for long double) ?
I guess that it is typo. I expect IEEE 32-bit in both cases.

Agreed. What I think has happened is that the table was entered using a spreadsheet tool, and it decided to auto-increment the number of bits when copy/pasting.

>variables are binary stored in memory
Yes they are.
But as C will use correct assembler instruction for it or emulate FPU in software etc, it needs to know the type.
Plus it also warns you from passing data with incompatible types to each other, but with type casting may be overridden.