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Compiler User Guide

Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler Coding Practices Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler Command-line Options Language Extensions Preprocessor extensions #assert #include_next #unassert #warning C99 language features available in C90 // comments Subscripting struct Flexible array members C99 language features available in C++ and C90 Variadic macros long long restrict Hexadecimal floats Standard C language extensions Constant expressions Array and pointer extensions Block scope function declarations Dollar signs in identifiers Top-level declarations Benign redeclarations External entities Function prototypes Standard C++ language extensions ? operator Declaration of a class member friend Read/write constants Scalar type constants Specialization of nonmember function templates Type conversions Standard C and Standard C++ language extensions Address of a register variable Arguments to functions Anonymous classes, structures and unions Assembler labels Empty declaration Hexadecimal floating-point constants Incomplete enums Integral type extensions Label definitions Long float Nonstatic local variables Structure, union, enum, and bitfield extensions GNU extensions to the C and C++ languages Compiler-specific Features C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Array and pointer extensions

8.17 Array and pointer extensions

The compiler supports a number of array and pointer extensions, for example permitting assignment between pointers to types that are interchangeable but not identical.

The following array and pointer extensions are supported:
  • Assignment and pointer differences are permitted between pointers to types that are interchangeable but not identical, for example, unsigned char * and char *. This includes pointers to same-sized integral types, typically, int * and long *. A warning is issued.
    Assignment of a string constant to a pointer to any kind of character is permitted without a warning.
  • Assignment of pointer types is permitted in cases where the destination type has added type qualifiers that are not at the top level, for example, assigning int ** to const int **. Comparisons and pointer difference of such pairs of pointer types are also permitted. A warning is issued.
  • In operations on pointers, a pointer to void is always implicitly converted to another type if necessary. Also, a null pointer constant is always implicitly converted to a null pointer of the right type if necessary. In ISO C, some operators permit these, and others do not.
  • Pointers to different function types can be assigned or compared for equality (==) or inequality (!=) without an explicit type cast. A warning or error is issued.
    This extension is prohibited in C++ mode.
  • A pointer to void can be implicitly converted to, or from, a pointer to a function type.
  • In an initializer, a pointer constant value can be cast to an integral type if the integral type is big enough to contain it.
  • A non lvalue array expression is converted to a pointer to the first element of the array when it is subscripted or similarly used.
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