GNU技术文档精粹 GNU C库技术手册 卷1 英文版PDF电子书下载

1 Introduction 1

1.1 Getting Started 1

1.2 Standards and Portability 1

1.2.1 ISO C 2

1.2.2 POSIX(The Portable Operating System Interface) 2

1.2.3 Berkeley Unix 3

1.2.4 SVID(The System V Interface Description) 3

1.2.5 XPG(The X/Open Portability Guide) 4

1.3 Using the Library 4

1.3.1 Header Files 4

1.3.2 Macro Definitions of Functions 5

1.3.3 Reserved Names 6

1.3.4 Feature Test Macros 8

1.4 Roadmap to the Manual 12

2 Error Reporting 17

2.1 Checking for Errors 17

2.2 Error Codes 18

2.3 Error Messages 30

3 Memory Allocation 33

3.1 Dynamic Memory Allocation Concepts 33

3.2 Dynamic Allocation and C 33

3.3 Unconstrained Allocation 34

3.3.1 Basic Storage Allocation 34

3.3.2 Examples of malloc 35

3.3.3 Freeing Memory Allocated with malloc 36

3.3.4 Changing the Size of a Block 37

3.3.5 Allocating Cleared Space 38

3.3.6 Efficiency Considerations for malloc 39

3.3.7 Allocating Aligned Memory Blocks 39

3.3.8 Malloc Tunable Parameters 39

3.3.9 Heap Consistency Checking 40

3.3.10 Storage Allocation Hooks 42

3.3.11 Statistics for Storage Allocation with malloc 45

3.3.12 Summary of malloc-Related Functions 46

3.4 Allocation Debugging 47

3.4.1 How to install the tracing functionality 47

3.4.2 Example program excerpts 48

3.4.3 Some more or less clever ideas 48

3.4.4 Interpreting the traces 49

3.5 Obstacks 51

3.5.1 Creating Obstacks 51

3.5.2 Preparing for Using Obstacks 52

3.5.3 Allocation in an Obstack 53

3.5.4 Freeing Objects in an Obstack 54

3.5.5 Obstack Functions and Macros 55

3.5.6 Growing Objects 56

3.5.7 Extra Fast Growing Objects 57

3.5.8 Status of an Obstack 59

3.5.9 Alignment of Data in Obstacks 60

3.5.10 Obstack Chunks 60

3.5.11 Summary of Obstack Functions 61

3.6 Automatic Storage with Variable Size 63

3.6.1 alloca Example 63

3.6.2 Advantages of alloca 64

3.6.3 Disadvantages of alloca 65

3.6.4 GNU C Variable-Size Arrays 65

4 Character Handling 67

4.1 Classification of Characters 67

4.2 Case Conversion 69

4.3 Character class determination for wide characters 70

4.4 Notes on using the wide character classes 74

4.5 Mapping of wide characters 75

5 String and Array Utilities 77

5.1 Representation of Strings 77

5.2 String and Array Conventions 78

5.3 String Length 78

5.4 Copying and Concatenation 79

5.5 String/Array Comparison 88

5.6 Collation Functions 91

5.7 Search Functions 94

5.8 Finding Tokens in a String 97

5.9 Encode Binary Data 100

5.10 Argz and Envz Vectors 102

5.10.1 Argz Functions 102

5.10.2 Envz Functions 104

6 Character Set Handling 107

6.1 Introduction to Extended Characters 107

6.2 Overview about Character Handling Functions 111

6.3 Restartable Multibyte Conversion Functions 111

6.3.1 Selecting the conversion and its properties 112

6.3.2 Representing the state of the conversion 113

6.3.3 Converting Single Characters 114

6.3.4 Converting Multibyte and Wide Character Strings 121

6.3.5 A Complete Multibyte Conversion Example 125

6.4 Non-reentrant Conversion Function 127

6.4.1 Non-reentrant Conversion of Single Characters 127

6.4.2 Non-reentrant Conversion of Strings 129

6.4.3 States in Non-reentrant Functions 130

6.5 Generic Charset Conversion 131

6.5.1 Generic Character Set Conversion Interface 132

6.5.2 A complete iconv example 136

6.5.3 Some Details about other iconv Implementations 138

6.5.4 The iconv Implementation in the GNU C library 140

6.5.4.1 Format of'gconv-modules'files 141

6.5.4.2 Finding the conversion path in iconv 143

6.5.4.3 iconv module data structures 143

6.5.4.4 iconv module interfaces 147

7 Locales and Internationalization 157

7.1 What Effects a Locale Has 157

7.2 Choosing a Locale 158

7.3 Categories of Activities that Locales Affect 158

7.4 How Programs Set the Locale 159

7.5 Standard Locales 161

7.6 Accessing Locale Information 162

7.6.1 localeconv:It is portable but 162

7.6.1.1 Generic Numeric Formatting Parameters 163

7.6.1.2 Printing the Currency Symbol 164

7.6.1.3 Printing the Sign of a Monetary Amount 166

7.6.2 Pinpoint Access to Locale Data 167

7.7 A dedicated function to format numbers 172

8 Message Translation 177

8.1 X/Open Message Catalog Handling 177

8.1.1 The catgets function family 178

8.1.2 Format of the message catalog files 181

8.1.3 Generate Message Catalogs files 183

8.1.4 How to use the catgets interface 185

8.1.4.1 Not using symbolic names 185

8.1.4.2 Using symbolic names 185

8.1.4.3 How does to this allow to develop 186

8.2 The Uniforum approach to Message Translation 188

8.2.1 The gettext family of functions 188

8.2.1.1 What has to be done to translate a message? 189

8.2.1.2 How to determine which catalog to be used 191

8.2.1.3 User influence on gettext 193

8.2.2 Programs to handle message catalogs for gettext 196

9 Searching and Sorting 199

9.1 Defining the Comparison Function 199

9.2 Array Search Function 199

9.3 Array Sort Function 200

9.4 Searching and Sorting Example 201

9.5 The hsearch function 204

9.6 The tsearch function 207

10 Pattern Matching 211

10.1 Wildcard Matching 211

10.2 Globbing 212

10.2.1 Calling glob 212

10.2.2 Flags for Globbing 214

10.2.3 More Flags for Globbing 216

10.3 Regular Expression Matching 218

10.3.1 POSIX Regular Expression Compilation 218

10.3.2 Flags for POSIX Regular Expressions 220

10.3.3 Matching a Compiled POSIX Regular Expression 221

10.3.4 Match Results with Subexpressions 222

10.3.5 Complications in Subexpression Matching 223

10.3.6 POSIX Regexp Matching Cleanup 223

10.4 Shell-Style Word Expansion 224

10.4.1 The Stages of Word Expansion 225

10.4.2 Calling wordexp 225

10.4.3 Flags for Word Expansion 227

10.4.4 wordexp Example 228

10.4.5 Details of Tilde Expansion 229

10.4.6 Details of Variable Substitution 229

11 Input/Output Overview 233

11.1 Input/Output Concepts 233

11.1.1 Streams and File Descriptors 233

11.1.2 File Position 234

11.2 File Names 235

11.2.1 Directories 235

11.2.2 File Name Resolution 236

11.2.3 File Name Errors 237

11.2.4 Portability of File Names 238

12 Input/Output on Streams 239

12.1 Streams 239

12.2 Standard Streams 239

12.3 Opening Streams 240

12.4 Closing Streams 243

12.5 Simple Output by Characters or Lines 244

12.6 Character Input 245

12.7 Line-Oriented Input 246

12.8 Unreading 248

12.8.1 What Unreading Means 248

12.8.2 Using ungetc To Do Unreading 249

12.9 Block Input/Output 250

12.10 Formatted Output 251

12.10.1 Formatted Output Basics 251

12.10.2 Output Conversion Syntax 252

12.10.3 Table of Output Conversions 254

12.10.4 Integer Conversions 255

12.10.5 Floating-Point Conversions 257

12.10.6 Other Output Conversions 259

12.10.7 Formatted Output Functions 261

12.10.8 Dynamically Allocating Formatted Output 262

12.10.9 Variable Arguments Output Functions 263

12.10.10 Parsing a Template String 266

12.10.11 Example of Parsing a Template String 267

12.11 Customizing printf 269

12.11.1 Registering New Conversions 269

12.11.2 Conversion Specifier Options 270

12.11.3 Defining the Output Handler 272

12.11.4 printf Extension Example 273

12.11.5 Predefined printf Handlers 274

12.12 Formatted Input 275

12.12.1 Formatted Input Basics 276

12.12.2 Input Conversion Syntax 277

12.12.3 Table of Input Conversions 278

12.12.4 Numeric Input Conversions 279

12.12.5 String Input Conversions 281

12.12.6 Dynamically Allocating String Conversions 282

12.12.7 Other Input Conversions 283

12.12.8 Formatted Input Functions 283

12.12.9 Variable Arguments Input Functions 284

12.13 End-Of-File and Errors 285

12.14 Text and Binary Streams 285

12.15 File Positioning 286

12.16 Portable File-Position Functions 289

12.17 Stream Buffering 291

12.17.1 Buffering Concepts 292

12.17.2 Flushing Buffers 292

12.1 7.3 Controlling Which Kind of Buffering 293

12.18 Other Kinds of Streams 295

12.18.1 String Streams 295

12.18.2 Obstack Streams 297

12.18.3 Programming Your Own Custom Streams 298

12.18.3.1 Custom Streams and Cookies 298

12.18.3.2 Custom Stream Hook Functions 300

12.19 Formatted Messages 301

12.19.1 Printing Formatted Messages 301

12.19.2 Adding Severity Classes 304

12.19.3 How to use fmtmsg and addseverity 304

13 Low-Level Input/Output 307

13.1 Opening and Closing Files 307

13.2 Input and Output Primitives 310

13.3 Setting the File Position of a Descriptor 315

13.4 Descriptors and Streams 318

13.5 Dangers of Mixing Streams and Descriptors 319

13.5.1 Linked Chanuels 320

13.5.2 Independent Channels 320

13.5.3 Cleaning Streams 321

13.6 Fast Scatter-Gather I/O 321

13.7 Memory-mapped I/O 323

13.8 Waiting for Input or Output 326

13.9 Synchronizing I/O operations 330

13.10 Perform I/O Operations in Parallel 331

13.10.1 Asynchronous Read and Write Operations 334

13.10.2 Getting the Status of AIO Operations 338

13.10.3 Getting into a Consistent State 340

13.10.4 Cancellation of AIO Operations 342

13.10.5 How to optimize the AIO implementation 343

13.11 Control Operations on Files 344

13.12 Duplicating Descriptors 345

13.13 File Descriptor Flags 347

13.14 File Status Flags 349

13.14.1 File Access Modes 349

13.14.2 Open-time Flags 350

13.14.3 I/O Operating Modes 352

13.14.4 Getting and Setting File Status Flags 353

13.15 File Locks 354

13.16 Interrupt-Driven Input 358

13.17 Generic I/O Control operations 359

14 File System Interface 361

14.1 Working Directory 361

14.2 Accessing Directories 363

14.2.1 Format of a Directory Entry 363

14.2.2 Opening a Directory Stream 364

14.2.3 Reading and Closing a Directory Stream 365

14.2.4 Simple Program to List a Directory 366

14.2.5 Random Access in a Directory Stream 367

14.2.6 Scanning the Content of a Directory 367

14.2.7 Simple Program to List a Directory,Mark II 369

14.3 Working with Directory Trees 370

14.4 Hard Links 374

14.5 Symbolic Links 375

14.6 Deleting Files 377

14.7 Renaming Files 378

14.8 Creating Directories 379

14.9 File Attributes 380

14.9.1 The meaning of the File Attributes 380

14.9.2 Reading the Attributes of a File 385

14.9.3 Testing the Type of a File 386

14.9.4 File Owner 388

14.9.5 The Mode Bits for Access Permission 389

14.9.6 How Your Access to a File is Decided 391

14.9.7 Assigning File Permissions 392

14.9.8 Testing Permission to Access a File 394

14.9.9 File Times 395

14.9.10 File Size 397

14.10 Making Special Files 400

14.11 Temporary Files 401

15 Pipes and FIFOs 405

15.1 Creating a Pipe 405

15.2 Pipe to a Subprocess 407

15.3 FIFO Special Files 409

15.4 Atomicity of Pipe I/O 410

16 Sockets 411

16.1 Socket Concepts 411

16.2 Communication Styles 412

16.3 Socket Addresses 413

16.3.1 Address Formats 414

16.3.2 Setting the Address of a Socket 415

16.3.3 Reading the Address of a Socket 416

16.4 Interface Naming 417

16.5 The Local Namespace 418

16.5.1 Local Namespace Concepts 418

16.5.2 Details of Local Namespace 418

16.5.3 Example of Local-Namespace Sockets 419

16.6 The Internet Namespace 420

16.6.1 Internet Socket Address Formats 421

16.6.2 Host Addresses 422

16.6.2.1 Internet Host Addresses 422

16.6.2.2 Host Address Data Type 424

16.6.2.3 Host Address Functions 425

16.6.2.4 Host Names 427

16.6.3 Internet Ports 431

16.6.4 The Services Database 432

16.6.5 Byte Order Conversion 433

16.6.6 Protocols Database 434

16.6.7 Internet Socket Example 436

16.7 Other Namespaces 437

16.8 Opening and Closing Sockets 437

16.8.1 Creating a Socket 437

16.8.2 Closing a Socket 438

16.8.3 Socket Pairs 439

16.9 Using Sockets with Connections 440

16.9.1 Making a Connection 440

16.9.2 Listening for Connections 441

16.9.3 Accepting Connections 442

16.9.4 Who is Connected to Me? 443

16.9.5 Transferring Data 444

16.9.5.1 Sending Data 444

16.9.5.2 Receiving Data 445

16.9.5.3 Socket Data Options 446

16.9.6 Byte Stream Socket Example 446

16.9.7 Byte Stream Connection Server Example 448

16.9.8 Out-of-Band Data 450

16.10 Datagram Socket Operations 454

16.10.1 Sending Datagrams 454

16.10.2 Receiving Datagrams 455

16.10.3 Datagram Socket Example 455

16.10.4 Example of Reading Datagrams 457

16.11 The inetd Daemon 458

16.11.1 inetd Servers 459

16.11.2 Configuring inetd 459

16.12 Socket Options 460

16.12.1 Socket Option Functions 460

16.12.2 Socket-Level Options 461

16.13 Networks Database 462

17 Low-Level Terminal Interface 465

17.1 Identifying Terminals 465

17.2 I/O Queues 466

17.3 Two Styles of Input:Canonical or Not 466

17.4 Terminal Modes 467

17.4.1 Terminal Mode Data Types 467

17.4.2 Terminal Mode Functions 468

17.4.3 Setting Terminal Modes Properly 470

17.4.4 Input Modes 471

17.4.5 Output Modes 473

17.4.6 Control Modes 474

17.4.7 Local Modes 476

17.4.8 Line Speed 479

17.4.9 Special Characters 480

17.4.9.1 Characters for Input Editing 481

17.4.9.2 Characters that Cause Signals 483

17.4.9.3 Special Characters for Flow Control 484

17.4.9.4 Other Special Characters 484

17.4.10 Noncanonical Input 485

17.5 Line Control Functions 487

17.6 Noncanonical Mode Example 489

17.7 Pseudo-Terminals 491

17.7.1 Allocating Pseudo-Terminals 491

17.7.2 Opening a Pseudo-Terminal Pair 493

18 Mathematics 495

18.1 Predefined Mathematical Constants 495

18.2 Trigonometric Functions 496

18.3 Inverse Trigonometric Functions 498

18.4 Exponentiation and Logarithms 499

18.5 Hyperbolic Functions 504

18.6 Special Functions 505

18.7 Pseudo-Random Numbers 508

18.7.1 ISO C Random Number Functions 508

18.7.2 BSD Random Number Functions 509

18.7.3 SVID Random Number Function 510

18.8 Is Fast Code or Small Code preferred? 515

19 Arithmetic Functions 517

19.1 Floating Point Numbers 517

19.2 Floating-Point Number Classification Functions 517

19.3 Errors in Floating-Point Calculations 519

19.3.1 FP Exceptions 519

19.3.2 Infinity and NaN 521

19.3.3 Examining the FPU status word 523

19.3.4 Error Reporting by Mathematical Functions 524

19.4 Rounding Modes 525

19.5 Floating-Point Control Functions 527

19.6 Arithmetic Functions 528

19.6.1 Absolute Value 528

19.6.2 Normalization Functions 529

19.6.3 Rounding Functions 531

19.6.4 Remainder Functions 532

19.6.5 Setting and modifying single bits of FP values 533

19.6.6 Floating-Point Comparison Functions 535

19.6.7 Miscellaneous FP arithmetic functions 536

19.7 Complex Numbers 537

19.8 Projections,Conjugates,and Decomposing of Complex 538

19.9 Integer Division 539

19.10 Parsing of Numbers 540

19.10.1 Parsing of Integers 541

19.10.2 Parsing of Floats 544

19.11 Old-fashioned System V number-to-string functions 545

20 Date and Time 549

20.1 Processor Time 549

20.1.1 Basic CPU Time Inquiry 549

20.1.2 Detailed Elapsed CPU Time Inquiry 550

20.2 Calendar Time 551

20.2.1 Simple Calendar Time 552

20.2.2 High-Resolution Calendar 552

20.2.3 Broken-down Time 555

20.2.4 Formatting Date and Time 558

20.2.5 Convert textual time and date information back 564

20.2.5.1 Interpret string according to given format 564

20.2.5.2 A user-friendlier way to parse times and dates 570

20.2.6 Specifying the Time Zone with TZ 572

20.2.7 Functions and Variables for Time Zones 575

20.2.8 Time Functions Example 576

20.3 Precision Time 576

20.4 Setting an Alarm 579

20.5 Sleeping 582

20.6 Resource Usage 583

20.7 Limiting Resource Usage 585

20.8 Process Priority 588

21 Non-Local Exits 591

21.1 Introduction to Non-Local Exits 591

21.2 Details of Non-Local Exits 593

21.3 Non-Local Exits and Signals 594

22 Signal Handling 595

22.1 Basic Concepts of Signals 595

22.1.1 Some Kinds of Signals 595

22.1.2 Concepts of Signal Generation 596

22.1.3 How Signals Are Delivered 596

22.2 Standard Signals 597

22.2.1 Program Error Signals 598

22.2.2 Termination Signals 601

22.2.3 Alarm Signals 602

22.2.4 Asynchronous I/O Signals 603

22.2.5 Job Control Signals 603

22.2.6 Operation Error Signals 605

22.2.7 Miscellaneous Signals 606

22.2.8 Signal Messages 607

22.3 Specifying Signal Actions 608

22.3.1 Basic Signal Handling 608

22.3.2 Advanced Signal Handling 610

22.3.3 Interaction of signal and sigaction 612

22.3.4 sigaction Function Example 612

22.3.5 Flags for sigaction 614

22.3.6 Initial Signal Actions 614

22.4 Defining Signal Handlers 615

22.4.1 Signal Handlers that Return 616

22.4.2 Handlers That Terminate the Process 617

22.4.3 Nonlocal Control Transfer in Handlers 618

22.4.4 Signals Arriving While a Handler Runs 619

22.4.5 Signals Close Together Merge into One 620

22.4.6 Signal Handling and Nonreentrant Functions 623

22.4.7 Atomic Data Access and Signal Handling 624

22.4.7.1 Problems with Non-Atomic Access 625

22.4.7.2 Atomic Types 626

22.4.7.3 Atomic Usage Patterns 626

22.5 Primitives Interrupted by Signals 627

22.6 Generating Signals 628

22.6.1 Signaling Yourself 628

22.6.2 Signaling Another Process 629

22.6.3 Permission for using kill 630

22.6.4 Using kill for Communication 631

22.7 Blocking Signals 633

22.7.1 Why Blocking Signals is Useful 633

22.7.2 Signal Sets 633

22.7.3 Process Signal Mask 635

22.7.4 Blocking to Test for Delivery of a Signal 636

22.7.5 Blocking Signals for a Handler 637

22.7.6 Checking for Pending Signals 638

22.7.7 Remembering a Signal to Act On Later 639

22.8 Waiting for a Signal 641

22.8.1 Using pause 641

22.8.2 Problems with pause 641

22.8.3 Using sigsuspend 642

22.9 Using a Separate Signal Stack 643

22.10 BSD Signal Handling 646

22.10.1 BSD Function to Establish a Handler 646

22.10.2 BSD Functions for Blocking Signals 647

23 Process Startup and Termination 649

23.1 Program Arguments 649

23.1.1 Program Argument Syntax Conventions 650

23.1.2 Parsing Program Arguments 651

23.2 Parsing program options using getopt 651

23.2.1 Using the getopt function 651

23.2.2 Example of Parsing Arguments with getopt 652

23.2.3 Parsing Long Options with getopt_long 654

23.2.4 Example of Parsing Long Options with getopt_long 656

23.3 Parsing Program Options with Argp 659

23.3.1 The argp_parse Function 659

23.3.2 Argp Global Variables 660

23.3.3 Specifying Argp Parsers 660

23.3.4 Specifying Options in an Argp Parser 662

23.3.4.1 Flags for Argp Options 663

23.3.5 Argp Parser Functions 664

23.3.5.1 Special Keys for Argp Parser Functions 665

23.3.5.2 Functions For Use in Argp Parsers 667

23.3.5.3 Argp Parsing State 668

23.3.6 Combining Multiple Argp Parsers 670

23.3.7 Flags for argp_parse 671

23.3.8 Customizing Argp Help Output 672

23.3.8.1 Special Keys for Argp Help Filter Functions 672

23.3.9 The argp_help Function 673

23.3.10 Flags for the argp_help Function 673

23.3.11 Argp Examples 675

23.3.11.1 A Minimal Program Using Argp 675

23.3.11.2 A Program Using Argp with Only Default Options 675

23.3.11.3 A Program Using Argp with User Options 677

23.3.11.4 A Program Using Multiple Combined Argp Parsers 681

23.3.12 Argp User Customization 681

23.3.12.5 Parsing of Suboptions 685

23.3.13 Parsing of Suboptions Example 686

23.4 Environment Variables 688

23.4.1 Environment Access 689

23.4.2 Standard Environment Variables 691

23.5 Program Termination 693

23.5.1 Normal Termination 693

23.5.2 Exit Status 694

23.5.3 Cleanups on Exit 694

23.5.4 Aborting a Program 696

23.5.5 Termination Internals 696

24 Processes 699

24.1 Running a Command 699

24.2 Process Creation Concepts 700

24.3 Process Identification 700

24.4 Creating a Process 701

24.5 Executing a File 702

24.6 Process Completion 705

24.7 Process Completion Status 708

24.8 BSD Process Wait Functions 709

24.9 Process Creation Example 710

25 Job Control 713

25.1 Concepts of Job Control 713

25.2 Job Control is Optional 714

25.3 Controlling Terminal of a Process 714

25.4 Access to the Controlling Terminal 715

25.5 Orphaned Process Groups 715

25.6 Implementing a Job Control Shell 716

25.6.1 Data Structures for the Shell 716

25.6.2 Initializing the Shell 718

25.6.3 Launching Jobs 720

25.6.4 Foreground and Background 724

25.6.5 Stopped and Terminated Jobs 725

25.6.6 Continuing Stopped Jobs 730

25.6.7 The Missing Pieces 730

25.7 Functions for Job Control 731

25.7.1 Identifying the Controlling Terminal 731

25.7.2 Process Group Functions 732

25.7.3 Functions for Controlling Terminal Access 734

26 System Databases and Name Service Switch 737

26.1 NSS Basics 737

26.2 The NSS Configuration File 738

26.2.1 Services in the NSS configuration File 739

26.2.2 Actions in the NSS configuration 739

26.2.3 Notes on the NSS Configuration File 740

26.3 NSS Module Internals 741

26.3.1 The Naming Scheme of the NSS Modules 741

26.3.2 The Interface of the Function in NSS Modules 742

26.4 Extending NSS 744

26.4.1 Adding another Service to NSS 744

26.4.2 Internals of the NSS Module Functions 745

27 Users and Groups 749

27.1 User and Group IDs 749

27.2 The Persona of a Process 749

27.3 Why Change the Persona of a Process? 750

27.4 How an Application Can Change Persona 751

27.5 Reading the Persona of a Process 751

27.6 Setting the User ID 752

27.7 Setting the Group IDs 753

27.8 Enabling and Disabling Setuid Access 755

27.9 Setuid Program Example 756

27.10 Tips for Writing Setuid Programs 759

27.11 Identifying Who Logged In 759

27.12 The User Accounting Database 760

27.12.1 Manipulating the User Accounting Database 761

27.12.2 XPG User Accounting Database Functions 766

27.12.3 Logging In and Out 768

27.13 User Database 769

27.13.1 The Data Structure that Describes a User 769

27.13.2 Looking Up One User 769

27.13.3 Scanning the List of All Users 770

27.13.4 Writing a User Entry 772

27.14 Group Database 772

27.14.1 The Data Structure for a Group 772

27.14.2 Looking Up One Group 772

27.14.3 Scanning the List of All Groups 773

27.15 User and Group Database Example 775

27.16 Netgroup Database 776

27.16.1 Netgroup Data 776

27.16.2 Looking up one Netgroup 777

27.16.3 Testing for Netgroup Membership 778

28 System Information 779

28.1 Host Identification 779

28.2 Hardware/Software Type Identification 780

28.3 Which filesystems are mounted and/or available? 781

29 System Configuration Parameters 789

29.1 General Capacity Limits 789

29.2 Overall System Options 790

29.3 Which Version of POSIX is Supported 792

29.4 Using sysconf 793

29.4.1 Definition of sysconf 793

29.4.2 Constants for sysconf Parameters 793

29.4.3 Examples of sysconf 801

29.5 Minimum Values for General Capacity Limits 802

29.6 Limits on File System Capacity 803

29.7 Optional Features in File Support 805

29.8 Minimum Values for File System Limits 806

29.9 Using pathconf 807

29.10 Utility Program Capacity Limits 808

29.11 Minimum Values for Utility Limits 809

29.12 String-Valued Parameters 810

30 DES Encryption and Password Handling 813

30.1 Legal Problems 813

30.2 Reading Passwords 814

30.3 Encrypting Passwords 815

30.4 DES Encryption 818

31 POSIX Threads 821

31.1 Basic Thread Operations 821

31.2 Thread Attributes 823

31.3 Cancellation 825

31.4 Cleanup Handlers 826

31.5 Mutexes 828

31.6 Condition Variables 832

31.7 POSIX Semaphores 835

31.8 Thread-Specific Data 836

31.9 Threads and Signal Handling 839

31.10 Miscellaneous Thread Functions 840

Appendix A C Language Facilities in the Library 845

A.1 Explicitly Checking Internal Consistency 845

A.2 Variadic Functions 846

A.2.1 Why Variadic Functions are Used 847

A.2.2 How Variadic Functions are Defined and Used 847

A.2.2.1 Syntax for Variable Arguments 848

A.2.2.2 Receiving the Argument Values 848

A.2.2.3 How Many Arguments Were Supplied 849

A.2.2.4 Calling Variadic Functions 850

A.2.2.5 Argument Access Macros 850

A.2.3 Example of a Variadic Function 852

A.2.3.1 Old-Style Variadic Functions 853

A.3 Null Pointer Constant 853

A.4 Important Data Types 854

A.5 Data Type Measurements 855

A.5.1 Computing the Width of an Integer Data Type 855

A.5.2 Range of an Integer Type 855

A.5.3 Floating Type Macros 857

A.5.3.1 Floating Point Representation Concepts 857

A.5.3.2 Floating Point Parameters 859

A.5.3.3 IEEE Floating Point 862

A.5.4 Structure Field Offset Measurement 863

App endix B Summary of Library Facilities 865

Appendix C Installing the GNU C Library 997

C.1 Configuring and compiling GNU Libc 997

C.2 Installing the C Library 1000

C.3 Recommended Tools for Compilation 1001

C.4 Supported Configurations 1003

C.5 Specific advice for Linux systems 1004

C.6 Reporting Bugs 1005

Appendix D Library Maintenance 1007

D.1 Adding New Functions 1007

D.2 Porting the GNU C Library 1008

D.2.1 Layout of the'sysdeps'Directory Hierarchy 1011

D.2.2 Porting the GNU C Library to Unix Systems 1014

Appendix E Contributors to the GNU C Library 1015

Appendix F GNU LIBRARY GENERAL PUBLIC LICENSE 1023

Preamble 1023

TERMS AND CONDITIONS FOR COPYING,DISTRIBUTION AND MODIFICATION 1025

How to Apply These Terms to Your New Libraries 1032

Concept Index 1033

Type Index 1047

Function and Macro Index 1051

Variable and Constant Macro Index 1067

Program and File Index 1079