Overview
A C program can be seen as a sort of machine that manipulates values: the particular values that variables of the program have at a given time, and also intermediate values that are the result of computed expressions.
This quote describes C’s abstract state machine. Whatever instructions a C program compiles down to is “unimportant” provided that all observable states are correctly reproduced. This is the essence of optimization.
Values
An object is a region of data storage in the execution environment, the contents of which can represent values. An lvalue is an expression (with non-void object type) that potentially designates an object. An rvalue is the “value of the expression.”
The notion of a value in C is an abstract entity. It exists beyond the program or the representation of the value in the program. For example, the value 0 (no matter how its represented) added to variable x should always yield result x regardless of platform.
Types
Types are additional properties that C associates with values. All values have a type that is statically determined and all possible operations on a value are determined by its type.
Representations
The binary representation of a type is the model used to represent values of said type on a given platform. The object representation of a type determines how values are stored in memory, disk, etc.
Bibliography
- “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.
- Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).