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 Numeric formatting convention inquiry

4.4.2.1 The localeconv function

4.5 Mathematics <math.h>

4.5.1 Treatment of error conditions
4.5.2 Trigonometric functions
4.5.2.1 The acos function

4.5.2.2 The asin function
4.5.2.3 The atan function
4.5.2.4 The atan2 function
4.5.2.5 The cos function
4.5.2.6 The sin function
4.5.2.7 The tan function

4.5.3 Hyperbolic functions

4.5.3.1 The cosh function
4.5.3.2 The sinh function
4.5.3.3 The tanh function

4.5.4 Exponential and logarithmic functions

4.5.4.1 The exp function
4.5.4.2 The frexp function
4.5.4.3 The ldexp function
4.5.4.4 The log function
4.5.4.5 The log10 function
4.5.4.6 The modf function

4.5.5 Power functions

4.5.5.1 The pow function
4.5.5.2 The sqrt function

4.5.6 Nearest integer, absolute value, and remainder functions

4.5.6.1 The ceil function
4.5.6.2 The fabs function
4.5.6.3 The floor function
4.5.6.4 The fmod function

4.6 Nonlocal jumps <setjmp.h>

4.6.1 Save calling environment

4.6.1.1 The setjmp macro

4.6.2 Restore calling environment

4.6.2.1 The longjmp function

4.7 Signal Handling <signal.h>

4.7.1 Specify signal handling

4.7.1.1 The signal function

4.7.2 Send signal

4.7.2.1 The raise function

4.8 Variable Arguments <stdarg.h>

4.8.1 Variable argument list access macros

4.8.1.1 The va_start macro
4.8.1.2 The va_arg macro
4.8.1.3 The va_end macro

4.9 Input/Output <stdio.h>

4.9.1 Introduction
4.9.2 Streams
4.9.3 Files
4.9.4 Operations on files

4.9.4.1 The remove function
4.9.4.2 The rename function
4.9.4.3 The tmpfile function
4.9.4.4 The tmpnam function

4.9.5 File access functions

4.9.5.1 The fclose function
4.9.5.2 The fflush function
4.9.5.3 The fopen function
4.9.5.4 The freopen function
4.9.5.5 The setbuf function
4.9.5.6 The setvbuf function

4.9.6 Formatted input/output functions

4.9.6.1 The fprintf function
4.9.6.2 The fscanf function
4.9.6.3 The printf function
4.9.6.4 The scanf function
4.9.6.5 The sprintf function
4.9.6.6 The sscanf function
4.9.6.7 The vfprintf function
4.9.6.8 The vprintf function
4.9.6.9 The vsprintf function

4.9.7 Character input/output functions

4.9.7.1 The fgetc function
4.9.7.2 The fgets function
4.9.7.3 The fputc function
4.9.7.4 The fputs function
4.9.7.5 The getc function
4.9.7.6 The getchar function
4.9.7.7 The gets function
4.9.7.8 The putc function
4.9.7.9 The putchar function
4.9.7.10 The puts function
4.9.7.11 The ungetc function

4.9.8 Direct input/output functions

4.9.8.1 The fread function
4.9.8.2 The fwrite function

4.9.9 File positioning functions

4.9.9.1 The fgetpos function
4.9.9.2 The fseek function
4.9.9.3 The fsetpos function
4.9.9.4 The ftell function
4.9.9.5 The rewind function

4.9.10 Error-handling functions

4.9.10.1 The clearerr function
4.9.10.2 The feof function
4.9.10.3 The ferror function
4.9.10.4 The perror function

4.10 General Utilities <stdlib.h>

4.10.1 String conversion functions

4.10.1.1 The atof function
4.10.1.2 The atoi function
4.10.1.3 The atol function
4.10.1.4 The strtod function
4.10.1.5 The strtol function
4.10.1.6 The strtoul function

4.10.2 Pseudo-random sequence generation functions

4.10.2.1 The rand function
4.10.2.2 The srand function

4.10.3 Memory management functions

4.10.3.1 The calloc function
4.10.3.2 The free function
4.10.3.3 The malloc function
4.10.3.4 The realloc function

4.10.4 Communication with the environment

4.10.4.1 The abort function
4.10.4.2 The atexit function
4.10.4.3 The exit function
4.10.4.4 The getenv function
4.10.4.5 The system function

4.10.5 Searching and sorting utilities

4.10.5.2 The bsearch function
4.10.5.1 The qsort function

4.10.6 Integer arithmetic functions

4.10.6.1 The abs function
4.10.6.2 The div function
4.10.6.3 The labs function
4.10.6.4 The ldiv function

4.10.7 Multibyte character functions

4.10.7.1 The mblen function
4.10.7.2 The mbtowc function
4.10.7.3 The wctomb function

4.10.8 Multibyte string functions

4.10.8.1 The mbstowcs function
4.10.8.2 The wcstombs function

4.11 String Handling <string.h>

4.11.1 String function conventions
4.11.2 Copying functions

4.11.2.1 The memcpy function
4.11.2.2 The memmove function
4.11.2.3 The strcpy function
4.11.2.4 The strncpy function

4.11.3 Concatenation functions

4.11.3.1 The strcat function
4.11.3.2 The strncat function

4.11.4 Comparison functions

4.11.4.1 The memcmp function
4.11.4.2 The strcmp function
4.11.4.3 The strcoll function
4.11.4.4 The strncmp function
4.11.4.5 The strxfrm function

4.11.5 Search functions

4.11.5.1 The memchr function
4.11.5.2 The strchr function
4.11.5.3 The strcspn function
4.11.5.4 The strpbrk function
4.11.5.5 The strrchr function
4.11.5.6 The strspn function
4.11.5.7 The strstr function
4.11.5.8 The strtok function

4.11.6 Miscellaneous functions

4.11.6.1 The memset function
4.11.6.2 The strerror function
4.11.6.3 The strlen function

4.12 Date and Time <time.h>

4.12.1 Components of time
4.12.2 Time manipulation functions

4.12.2.1 The clock function
4.12.2.2 The difftime function
4.12.2.3 The mktime function
4.12.2.4 The time function

4.12.3 Time conversion functions

4.12.3.1 The asctime function
4.12.3.2 The ctime function
4.12.3.3 The gmtime function
4.12.3.4 The localtime function
4.12.3.5 The strftime function

4.13 Future library directions

4.13.1 Errors <errno.h>
4.13.2 Character handling <ctype.h>
4.13.3 Localization <locale.h>
4.13.4 Mathematics <math.h>
4.13.5 Signal handling <signal.h>
4.13.6 Input/output <stdio.h>
4.13.7 General utilities <stdlib.h>
4.13.8 String handling <string.h>

5 Appendices