Rationale for

American National Standard
      for Information Systems -
      Programming Language -

C

      (This Rationale is not part of American National Standard X3.159-1989, but is included for information only.)

UNIX is a registered trademark of AT&T.
DEC and PDP-11 are trademarks of Digital Equipment Corporation.
POSIX is a trademark of IEEE.

Contents

1  Introduction

1.1  Purpose
1.2  Scope
1.3  References
1.4  Organization of the document
1.5  Base documents
1.6  Definitions of terms
1.7  Compliance
1.8  Future directions

2  Environment

2.1  Conceptual models
2.1.1  Translation environment

2.1.1.1  Program structure
2.1.1.2  Translation phases
2.1.1.3  Diagnostics

2.1.2  Execution environments

2.1.2.1  Freestanding environment
2.1.2.2  Hosted environment
2.1.2.3  Program execution

2.2  Environmental considerations

2.2.1  Character sets

2.2.1.1  Trigraph sequences
2.2.1.2  Multibyte characters

2.2.2  Character display semantics
2.2.3  Signals and interrupts
2.2.4  Environmental limits

2.2.4.1  Translation limits
2.2.4.2  Numerical limits

2.2.4.2.1  Sizes of integral types <limits.h>
2.2.4.2.2  Characteristics of floating types <float.h>

3  Language

3.1  Lexical Elements

3.1.1  Keywords
3.1.2  Identifiers

3.1.2.1  Scopes of identifiers
3.1.2.2  Linkages of identifiers
3.1.2.3  Name spaces of identifiers
3.1.2.4  Storage durations of objects
3.1.2.5  Types
3.1.2.6  Compatible type and composite type

3.1.3  Constants

3.1.3.1  Floating constants
3.1.3.2  Integer constants
3.1.3.3  Enumeration constants
3.1.3.4  Character constants

3.1.4  String literals
3.1.5  Operators
3.1.6  Punctuators
3.1.7  Header names
3.1.8  Preprocessing numbers
3.1.9  Comments

3.2  Conversions

3.2.1  Arithmetic operands

3.2.1.1  Characters and integers
3.2.1.2  Signed and unsigned integers
3.2.1.3  Floating and integral
3.2.1.4  Floating types
3.2.1.5  Usual arithmetic conversions

3.2.2  Other operands

3.2.2.1  Lvalues and function designators
3.2.2.2  void
3.2.2.3  Pointers

3.3  Expressions

3.3.1  Primary expressions
3.3.2  Postfix operators

3.3.2.1  Array subscripting
3.3.2.2  Function calls
3.3.2.3  Structure and union members
3.3.2.4  Postfix increment and decrement operators

3.3.3  Unary operators

3.3.3.1  Prefix increment and decrement operators
3.3.3.2  Address and indirection operators
3.3.3.3  Unary arithmetic operators
3.3.3.4  The sizeof operator

3.3.4  Cast operators
3.3.5  Multiplicative operators
3.3.6  Additive operators
3.3.7  Bitwise shift operators
3.3.8  Relational operators
3.3.9  Equality operators
3.3.10  Bitwise AND operator
3.3.11  Bitwise exclusive OR operator
3.3.12  Bitwise inclusive OR operator
3.3.13  Logical AND operator
3.3.14  Logical OR operator
3.3.15  Conditional operator
3.3.16  Assignment operators

3.3.16.1  Simple assignment
3.3.16.2  Compound assignment

3.3.17  Comma operator

3.4  Constant Expressions
3.5  Declarations

3.5.1  Storage-class specifiers
3.5.2  Type specifiers

3.5.2.1  Structure and union specifiers
3.5.2.2  Enumeration specifiers
3.5.2.3  Tags

3.5.3  Type qualifiers
3.5.4  Declarators

3.5.4.1  Pointer declarators
3.5.4.2  Array declarators
3.5.4.3  Function declarators (including prototypes)

3.5.5  Type names
3.5.6  Type definitions
3.5.7  Initialization

3.6  Statements

3.6.1  Labeled statements
3.6.2  Compound statement, or block
3.6.3  Expression and null statements
3.6.4  Selection statements

3.6.4.1  The if statement
3.6.4.2  The switch statement

3.6.5  Iteration statements

3.6.5.1  The while statement
3.6.5.2  The do statement
3.6.5.3  The for statement

3.6.6  Jump statements

3.6.6.1  The goto statement
3.6.6.2  The continue statement
3.6.6.3  The break statement
3.6.6.4  The return statement

3.7  External definitions

3.7.1  Function definitions
3.7.2  External object definitions

3.8  Preprocessing directives

3.8.1  Conditional inclusion
3.8.2  Source file inclusion
3.8.3  Macro replacement

3.8.3.1  Argument substitution
3.8.3.2  The # operator
3.8.3.3  The ## operator
3.8.3.4  Rescanning and further replacement
3.8.3.5  Scope of macro definitions

3.8.4  Line control
3.8.5  Error directive
3.8.6  Pragma directive
3.8.7  Null directive
3.8.8  Predefined macro names

3.9  Future language directions

3.9.1  External names
3.9.2  Character escape sequences
3.9.3  Storage-class specifiers
3.9.4  Function declarators
3.9.5  Function definitions
3.9.6  Array parameters

4  Library

4.1  Introduction

4.1.1  Definitions of terms
4.1.2  Standard headers

4.1.2.1  Reserved identifiers

4.1.3  Errors  <errno.h>
4.1.4  Limits  <float.h> and <limits.h>
4.1.5  Common definitions  <stddef.h>
4.1.6  Use of library functions

4.2  Diagnostics  <assert.h>

4.2.1  Program diagnostics

4.2.1.1  The assert macro

4.3  Character Handling  <ctype.h>

4.3.1  Character testing functions

4.3.1.1  The isalnum function
4.3.1.2  The isalpha function
4.3.1.3  The iscntrl function
4.3.1.4  The isdigit function
4.3.1.5  The isgraph function
4.3.1.6  The islower function
4.3.1.7  The isprint function
4.3.1.8  The ispunct function
4.3.1.9  The isspace function
4.3.1.10  The isupper function
4.3.1.11  The isxdigit function

4.3.2  Character case mapping functions

4.3.2.1  The tolower function
4.3.2.2  The toupper function

4.4  Localization  <locale.h>

4.4.1  Locale control

4.4.1.1  The setlocale function

4.4.2