How Does C Differ Subtly from C in Terms of Compilation and Syntax?

C's Subtle Departures from C

While it's widely believed that C is a subset of C , a closer examination reveals subtle differences. Here are some instances where code that compiles in C encounters obstacles in C :

No Tentative Definitions

In C , redefining variables is illegal, unlike in C, where tentative definitions allow for subsequent redefinitions.

Array Type Incompatibility

C distinguishes between array types with sizes and without, making int[] and int[N] incompatible. C, however, allows them to be used interchangeably.

K&R Function Syntax

C disallows the K&R style of function definition where the function parameter list directly follows the return type.

Nested Struct Scope

C defines nested structs to have class scope, while C adheres to the earlier behavior of local scope.

Default int

In C , using "auto" without an explicit type specifier is invalid, unlike in C, where it defaults to int.

Additional C99 Incompatibilities

C99 introduced further discrepancies:

Array Dimension Specifiers

C disallows declaration specifiers in array dimensions of function parameters, which is permitted in C.

Variable Length Arrays

C omits support for variable length arrays, whereas C allows them by declaring arrays with non-constant sizes.

Flexible Array Members

C lacks flexible array members within structs, a feature present in C.

Restrict Qualifier

C introduces the restrict qualifier to assist in aliasing analysis, but it's not supported in C.

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