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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

Constant expressions

8.16 Constant expressions

Extended constant expressions are supported in initializers.

The following examples show the compiler behavior for the default, --strict_warnings, and --strict compiler modes.

Example 1, assigning the address of variable

Your code might contain constant expressions that assign the address of a variable at file scope, for example:
int i;
int j = (int)&i; /* but not allowed by ISO */
When compiling for C, this produces the following behavior:
  • In default mode a warning is produced.
  • In --strict_warnings mode a warning is produced.
  • In --strict mode, an error is produced.

Example 2, constant value initializers

The following table compares the behavior of the ARM compilation tools with the ISO C Standard.
If compiling with --strict_warnings in place of --strict, the example source code that is not valid with --strict become valid. The --strict error message is downgraded to a warning message.

Table 8-1 Behavior of constant value initializers in comparison with ISO Standard C

Example source code ISO C Standard ARM compilation tools
--strict mode Nonstrict mode
extern int const c = 10; Valid Valid Valid
extern int const x = c + 10; Not valid Not valid Valid
static int y = c + 10; Not valid Not valid Valid
static int const z = c + 10; Not valid Not valid Valid
extern int *const cp = (int*)0x100; Valid Valid Valid
extern int *const xp = cp + 0x100; Not valid Not valid Valid
static int *yp = cp + 0x100; Not valid Not valid Valid
static int *const zp = cp + 0x100; Not valid Not valid Valid
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