Autoconf Creating Automatic Configuration Scripts for version 2.62, 8 April 2008 David MacKenzie Ben Elliston Akim Demaille This manual is for GNU Autoconf (version 2.62, 8 April 2008), a package for creating scripts to configure source code packages using templates and an M4 macro package. Copyright c 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.” (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.” i Table of Contents 1 Introduction............................... 1 2 The GNU Build System .................... 3 2.1 Automake .................................................. 3 2.2 Gnulib ..................................................... 3 2.3 Libtool ..................................................... 4 2.4 Pointers .................................................... 4 3 Making configure Scripts................... 5 3.1 Writing ‘configure.ac’...................................... 6 3.1.1 A Shell Script Compiler ................................. 6 3.1.2 The Autoconf Language ................................. 7 3.1.3 Standard ‘configure.ac’ Layout ........................ 8 3.2 Using autoscan to Create ‘configure.ac’ .................... 9 3.3 Using ifnames to List Conditionals .......................... 10 3.4 Using autoconf to Create configure ........................ 10 3.5 Using autoreconf to Update configure Scripts .............. 13 4 Initialization and Output Files............. 15 4.1 Initializing configure ...................................... 15 4.2 Dealing with Autoconf versions.............................. 16 4.3 Notices in configure ....................................... 16 4.4 Finding configure Input ................................... 17 4.5 Outputting Files ........................................... 18 4.6 Performing Configuration Actions ........................... 18 4.7 Creating Configuration Files ................................ 20 4.8 Substitutions in Makefiles ................................... 21 4.8.1 Preset Output Variables................................ 21 4.8.2 Installation Directory Variables ......................... 24 4.8.3 Changed Directory Variables ........................... 27 4.8.4 Build Directories ...................................... 28 4.8.5 Automatic Remaking .................................. 29 4.9 Configuration Header Files .................................. 30 4.9.1 Configuration Header Templates ........................ 31 4.9.2 Using autoheader to Create ‘config.h.in’.............. 31 4.9.3 Autoheader Macros .................................... 33 4.10 Running Arbitrary Configuration Commands ................ 33 4.11 Creating Configuration Links............................... 34 4.12 Configuring Other Packages in Subdirectories................ 35 4.13 Default Prefix............................................. 35 ii Autoconf 5 Existing Tests ............................ 37 5.1 Common Behavior ......................................... 37 5.1.1 Standard Symbols ..................................... 37 5.1.2 Default Includes ....................................... 37 5.2 Alternative Programs ....................................... 38 5.2.1 Particular Program Checks ............................. 39 5.2.2 Generic Program and File Checks ....................... 41 5.3 Files ...................................................... 44 5.4 Library Files ............................................... 44 5.5 Library Functions .......................................... 45 5.5.1 Portability of C Functions .............................. 45 5.5.2 Particular Function Checks ............................. 48 5.5.3 Generic Function Checks ............................... 54 5.6 Header Files ............................................... 56 5.6.1 Portability of Headers .................................. 56 5.6.2 Particular Header Checks............................... 58 5.6.3 Generic Header Checks ................................. 63 5.7 Declarations ............................................... 64 5.7.1 Particular Declaration Checks .......................... 64 5.7.2 Generic Declaration Checks............................. 64 5.8 Structures ................................................. 65 5.8.1 Particular Structure Checks ............................ 65 5.8.2 Generic Structure Checks............................... 66 5.9 Types ..................................................... 67 5.9.1 Particular Type Checks ................................ 67 5.9.2 Generic Type Checks .................................. 69 5.10 Compilers and Preprocessors ............................... 70 5.10.1 Specific Compiler Characteristics ...................... 70 5.10.2 Generic Compiler Characteristics ...................... 71 5.10.3 C Compiler Characteristics ............................ 72 5.10.4 C++ Compiler Characteristics .......................... 78 5.10.5 Objective C Compiler Characteristics .................. 78 5.10.6 Erlang Compiler and Interpreter Characteristics......... 79 5.10.7 Fortran Compiler Characteristics....................... 79 5.11 System Services ........................................... 84 5.12 Posix Variants ............................................ 85 5.13 Erlang Libraries........................................... 86 6 Writing Tests............................. 89 6.1 Language Choice ........................................... 89 6.2 Writing Test Programs ..................................... 90 6.2.1 Guidelines for Test Programs ........................... 91 6.2.2 Test Functions......................................... 91 6.2.3 Generating Sources .................................... 92 6.3 Running the Preprocessor ................................... 94 6.4 Running the Compiler ...................................... 95 6.5 Running the Linker......................................... 96 6.6 Checking Runtime Behavior................................. 96 iii 6.7 Systemology ............................................... 98 6.8 Multiple Cases ............................................. 98 7 Results of Tests ......................... 101 7.1 Defining C Preprocessor Symbols ........................... 101 7.2 Setting Output Variables .................................. 102 7.3 Special Characters in Output Variables ..................... 104 7.4 Caching Results ........................................... 105 7.4.1 Cache Variable Names ................................ 106 7.4.2 Cache Files .......................................... 106 7.4.3 Cache Checkpointing.................................. 107 7.5 Printing Messages ......................................... 108 8 Programming in M4 ..................... 111 8.1 M4 Quotation............................................. 111 8.1.1 Active Characters .................................... 111 8.1.2 One Macro Call ...................................... 112 8.1.3 Quoting and Parameters .............................. 113 8.1.4 Quotation and Nested Macros ......................... 114 8.1.5 changequote is Evil .................................. 115 8.1.6 Quadrigraphs......................................... 116 8.1.7 Quotation Rule Of Thumb ............................ 117 8.2 Using autom4te ........................................... 118 8.2.1 Invoking autom4te.................................... 118 8.2.2 Customizing autom4te ................................ 122 8.3 Programming in M4sugar .................................. 123 8.3.1 Redefined M4 Macros ................................. 123 8.3.2 Diagnostic messages from M4sugar ..................... 125 8.3.3 Diversion support..................................... 126 8.3.4 Conditional constructs ................................ 128 8.3.5 Looping constructs ................................... 129 8.3.6 Evaluation Macros .................................... 131 8.3.7 String manipulation in M4 ............................ 134 8.3.8 Arithmetic computation in M4......................... 137 8.3.9 Forbidden Patterns ................................... 139 8.4 Programming in M4sh ..................................... 139 8.5 File Descriptor Macros .................................... 141 9 Writing Autoconf Macros ................ 143 9.1 Macro Definitions ......................................... 143 9.2 Macro Names ............................................. 143 9.3 Reporting Messages ....................................... 145 9.4 Dependencies Between Macros ............................. 145 9.4.1 Prerequisite Macros ................................... 145 9.4.2 Suggested Ordering ................................... 147 9.4.3 One-Shot Macros ..................................... 147 9.5 Obsoleting Macros ........................................ 148 9.6 Coding Style .............................................. 148 iv Autoconf 10 Portable Shell Programming ............ 153 10.1 Shellology ............................................... 153 10.2 Here-Documents ........................................