D.1 Extensions Compatible with ANSI C

• Relaxed pointer and pointer/integer compatibility is allowed. That is, all pointer and integer types are compatible, and pointer types are compatible with each other regardless of the type of object they point to. Therefore, under the common C option, a pointer to float is compatible with a pointer to int .

• The digits 8 and 9 are valid in octal integer constants. (A warning message is issued by the compiler, however.)

• Bit-field data types may include enum , short , char , and long . The ANSI C Standard allows only int , unsigned int , or signed int .

• long float is recognized as a synonym for double .

• A third argument to the function main() , namely char *envp[] , is allowed.[1]

  When DEC C is run in common C compatibility mode, the main function can accept a third parameter, the environment array envp. This array contains process information such as the user name and controlling information, and has no bearing on passing command- line arguments. Its primary use is during exec and getenv library function calls.

  See your platform-specific DEC C documentation for more information about invoking the main function within your host environment.

• Text is allowed following the preprocessing directives #else and #endif .

• Address constants may be cast to int .

• Tentative definitions that exist at the completion of a compilation remain tentative to the linker, in accordance with the traditional model of definition resolution.

• Casts that do not cause a change in representation are legal as lvalues.

• Implicit function declarations are created at file level, rather than at block level.

• The types int and long are compatible.

• Taking the address of a variable with the register storage class is allowed.

• Block-level declarations of functions with static storage class are allowed.

• In array types, the element types are allowed to be incomplete.

• The type of a tentatively-defined variable is allowed to be incomplete at the end of the compilation unit. A warning is issued for this case.

• Values in case labels are allowed to have a pointer type.

• Trailing (extra) commas are allowed in enumeration lists.

• The semicolon following the last structure or union member may be omitted.

• Carriage returns are accepted and treated as white space.

[1] Parameters to the function main() are only checked in strict ANSI mode.