GCC Online Documents

This file documents the use of the GNU compilers. Copyright © 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 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 the Invariant Sections being “Funding Free Software”, the Front-Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled “GNU Free Documentation License”.

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.

Short Contents

• Introduction
• 1 Programming Languages Supported by GCC
• 2 Language Standards Supported by GCC
• 3 GCC Command Options
• 4 C Implementation-defined behavior
• 5 Extensions to the C Language Family
• 6 Extensions to the C++ Language
• 7 GNU Objective-C runtime features
• 8 Binary Compatibility
• 9 gcov—a Test Coverage Program
• 10 Known Causes of Trouble with GCC
• 11 Reporting Bugs
• 12 How To Get Help with GCC
• 13 Contributing to GCC Development
• Funding Free Software
• The GNU Project and GNU/Linux
• GNU General Public License
• GNU Free Documentation License
• Contributors to GCC
• Option Index
• Keyword Index

Table of Contents

• Introduction
• 1 Programming Languages Supported by GCC
• 2 Language Standards Supported by GCC
  • 2.1 C language
  • 2.2 C++ language
  • 2.3 Objective-C and Objective-C++ languages
• 3 GCC Command Options
  • 3.1 Option Summary
  • 3.2 Options Controlling the Kind of Output
  • 3.3 Compiling C++ Programs
  • 3.4 Options Controlling C Dialect
  • 3.5 Options Controlling C++ Dialect
  • 3.6 Options Controlling Objective-C and Objective-C++ Dialects
  • 3.7 Options to Control Diagnostic Messages Formatting
  • 3.8 Options to Request or Suppress Warnings
  • 3.9 Options for Debugging Your Program or GCC
  • 3.10 Options That Control Optimization
  • 3.11 Options Controlling the Preprocessor
  • 3.12 Passing Options to the Assembler
  • 3.13 Options for Linking
  • 3.14 Options for Directory Search
  • 3.15 Specifying subprocesses and the switches to pass to them
  • 3.16 Specifying Target Machine and Compiler Version
  • 3.17 Hardware Models and Configurations
    • 3.17.1 ARC Options
    • 3.17.2 ARM Options
    • 3.17.3 AVR Options
    • 3.17.4 Blackfin Options
    • 3.17.5 CRIS Options
    • 3.17.6 CRX Options
    • 3.17.7 Darwin Options
    • 3.17.8 DEC Alpha Options
    • 3.17.9 DEC Alpha/VMS Options
    • 3.17.10 FRV Options
    • 3.17.11 GNU/Linux Options
    • 3.17.12 H8/300 Options
    • 3.17.13 HPPA Options
    • 3.17.14 Intel 386 and AMD x86-64 Options
    • 3.17.15 IA-64 Options
    • 3.17.16 M32C Options
    • 3.17.17 M32R/D Options
    • 3.17.18 M680x0 Options
    • 3.17.19 M68hc1x Options
    • 3.17.20 MCore Options
    • 3.17.21 MIPS Options
    • 3.17.22 MMIX Options
    • 3.17.23 MN10300 Options
    • 3.17.24 PDP-11 Options
    • 3.17.25 picoChip Options
    • 3.17.26 PowerPC Options
    • 3.17.27 IBM RS/6000 and PowerPC Options
    • 3.17.28 S/390 and zSeries Options
    • 3.17.29 Score Options
    • 3.17.30 SH Options
    • 3.17.31 SPARC Options
    • 3.17.32 SPU Options
    • 3.17.33 Options for System V
    • 3.17.34 V850 Options
    • 3.17.35 VAX Options
    • 3.17.36 VxWorks Options
    • 3.17.37 x86-64 Options
    • 3.17.38 Xstormy16 Options
    • 3.17.39 Xtensa Options
    • 3.17.40 zSeries Options
  • 3.18 Options for Code Generation Conventions
  • 3.19 Environment Variables Affecting GCC
  • 3.20 Using Precompiled Headers
  • 3.21 Running Protoize
• 4 C Implementation-defined behavior
  • 4.1 Translation
  • 4.2 Environment
  • 4.3 Identifiers
  • 4.4 Characters
  • 4.5 Integers
  • 4.6 Floating point
  • 4.7 Arrays and pointers
  • 4.8 Hints
  • 4.9 Structures, unions, enumerations, and bit-fields
  • 4.10 Qualifiers
  • 4.11 Declarators
  • 4.12 Statements
  • 4.13 Preprocessing directives
  • 4.14 Library functions
  • 4.15 Architecture
  • 4.16 Locale-specific behavior
• 5 Extensions to the C Language Family
  • 5.1 Statements and Declarations in Expressions
  • 5.2 Locally Declared Labels
  • 5.3 Labels as Values
  • 5.4 Nested Functions
  • 5.5 Constructing Function Calls
  • 5.6 Referring to a Type with typeof
  • 5.7 Conditionals with Omitted Operands
  • 5.8 Double-Word Integers
  • 5.9 Complex Numbers
  • 5.10 Additional Floating Types
  • 5.11 Decimal Floating Types
  • 5.12 Hex Floats
  • 5.13 Fixed-Point Types
  • 5.14 Arrays of Length Zero
  • 5.15 Structures With No Members
  • 5.16 Arrays of Variable Length
  • 5.17 Macros with a Variable Number of Arguments.
  • 5.18 Slightly Looser Rules for Escaped Newlines
  • 5.19 Non-Lvalue Arrays May Have Subscripts
  • 5.20 Arithmetic on void- and Function-Pointers
  • 5.21 Non-Constant Initializers
  • 5.22 Compound Literals
  • 5.23 Designated Initializers
  • 5.24 Case Ranges
  • 5.25 Cast to a Union Type
  • 5.26 Mixed Declarations and Code
  • 5.27 Declaring Attributes of Functions
  • 5.28 Attribute Syntax
  • 5.29 Prototypes and Old-Style Function Definitions
  • 5.30 C++ Style Comments
  • 5.31 Dollar Signs in Identifier Names
  • 5.32 The Character <ESC> in Constants
  • 5.33 Inquiring on Alignment of Types or Variables
  • 5.34 Specifying Attributes of Variables
    • 5.34.1 Blackfin Variable Attributes
    • 5.34.2 M32R/D Variable Attributes
    • 5.34.3 i386 Variable Attributes
    • 5.34.4 PowerPC Variable Attributes
    • 5.34.5 SPU Variable Attributes
    • 5.34.6 Xstormy16 Variable Attributes
    • 5.34.7 AVR Variable Attributes
  • 5.35 Specifying Attributes of Types
    • 5.35.1 ARM Type Attributes
    • 5.35.2 i386 Type Attributes
    • 5.35.3 PowerPC Type Attributes
    • 5.35.4 SPU Type Attributes
  • 5.36 An Inline Function is As Fast As a Macro
  • 5.37 Assembler Instructions with C Expression Operands
    • 5.37.1 Size of an asm
    • 5.37.2 i386 floating point asm operands
  • 5.38 Constraints for asm Operands
    • 5.38.1 Simple Constraints
    • 5.38.2 Multiple Alternative Constraints
    • 5.38.3 Constraint Modifier Characters
    • 5.38.4 Constraints for Particular Machines
  • 5.39 Controlling Names Used in Assembler Code
  • 5.40 Variables in Specified Registers
    • 5.40.1 Defining Global Register Variables
    • 5.40.2 Specifying Registers for Local Variables
  • 5.41 Alternate Keywords
  • 5.42 Incomplete enum Types
  • 5.43 Function Names as Strings
  • 5.44 Getting the Return or Frame Address of a Function
  • 5.45 Using vector instructions through built-in functions
  • 5.46 Offsetof
  • 5.47 Built-in functions for atomic memory access
  • 5.48 Object Size Checking Builtins
  • 5.49 Other built-in functions provided by GCC
  • 5.50 Built-in Functions Specific to Particular Target Machines
    • 5.50.1 Alpha Built-in Functions
    • 5.50.2 ARM iWMMXt Built-in Functions
    • 5.50.3 ARM NEON Intrinsics
      • 5.50.3.1 Addition
      • 5.50.3.2 Multiplication
      • 5.50.3.3 Multiply-accumulate
      • 5.50.3.4 Multiply-subtract
      • 5.50.3.5 Subtraction
      • 5.50.3.6 Comparison (equal-to)
      • 5.50.3.7 Comparison (greater-than-or-equal-to)
      • 5.50.3.8 Comparison (less-than-or-equal-to)
      • 5.50.3.9 Comparison (greater-than)
      • 5.50.3.10 Comparison (less-than)
      • 5.50.3.11 Comparison (absolute greater-than-or-equal-to)
      • 5.50.3.12 Comparison (absolute less-than-or-equal-to)
      • 5.50.3.13 Comparison (absolute greater-than)
      • 5.50.3.14 Comparison (absolute less-than)
      • 5.50.3.15 Test bits
      • 5.50.3.16 Absolute difference
      • 5.50.3.17 Absolute difference and accumulate
      • 5.50.3.18 Maximum
      • 5.50.3.19 Minimum
      • 5.50.3.20 Pairwise add
      • 5.50.3.21 Pairwise add, single_opcode widen and accumulate
      • 5.50.3.22 Folding maximum
      • 5.50.3.23 Folding minimum
      • 5.50.3.24 Reciprocal step
      • 5.50.3.25 Vector shift left
      • 5.50.3.26 Vector shift left by constant
      • 5.50.3.27 Vector shift right by constant
      • 5.50.3.28 Vector shift right by constant and accumulate
      • 5.50.3.29 Vector shift right and insert
      • 5.50.3.30 Vector shift left and insert
      • 5.50.3.31 Absolute value
      • 5.50.3.32 Negation
      • 5.50.3.33 Bitwise not
      • 5.50.3.34 Count leading sign bits
      • 5.50.3.35 Count leading zeros
      • 5.50.3.36 Count number of set bits
      • 5.50.3.37 Reciprocal estimate
      • 5.50.3.38 Reciprocal square-root estimate
      • 5.50.3.39 Get lanes from a vector
      • 5.50.3.40 Set lanes in a vector
      • 5.50.3.41 Create vector from literal bit pattern
      • 5.50.3.42 Set all lanes to the same value
      • 5.50.3.43 Combining vectors
      • 5.50.3.44 Splitting vectors
      • 5.50.3.45 Conversions
      • 5.50.3.46 Move, single_opcode narrowing
      • 5.50.3.47 Move, single_opcode long
      • 5.50.3.48 Table lookup
      • 5.50.3.49 Extended table lookup
      • 5.50.3.50 Multiply, lane
      • 5.50.3.51 Long multiply, lane
      • 5.50.3.52 Saturating doubling long multiply, lane
      • 5.50.3.53 Saturating doubling multiply high, lane
      • 5.50.3.54 Multiply-accumulate, lane
      • 5.50.3.55 Multiply-subtract, lane
      • 5.50.3.56 Vector multiply by scalar
      • 5.50.3.57 Vector long multiply by scalar
      • 5.50.3.58 Vector saturating doubling long multiply by scalar
      • 5.50.3.59 Vector saturating doubling multiply high by scalar
      • 5.50.3.60 Vector multiply-accumulate by scalar
      • 5.50.3.61 Vector multiply-subtract by scalar
      • 5.50.3.62 Vector extract
      • 5.50.3.63 Reverse elements
      • 5.50.3.64 Bit selection
      • 5.50.3.65 Transpose elements
      • 5.50.3.66 Zip elements
      • 5.50.3.67 Unzip elements
      • 5.50.3.68 Element/structure loads, VLD1 variants
      • 5.50.3.69 Element/structure stores, VST1 variants
      • 5.50.3.70 Element/structure loads, VLD2 variants
      • 5.50.3.71 Element/structure stores, VST2 variants
      • 5.50.3.72 Element/structure loads, VLD3 variants
      • 5.50.3.73 Element/structure stores, VST3 variants
      • 5.50.3.74 Element/structure loads, VLD4 variants
      • 5.50.3.75 Element/structure stores, VST4 variants
      • 5.50.3.76 Logical operations (AND)
      • 5.50.3.77 Logical operations (OR)
      • 5.50.3.78 Logical operations (exclusive OR)
      • 5.50.3.79 Logical operations (AND-NOT)
      • 5.50.3.80 Logical operations (OR-NOT)
      • 5.50.3.81 Reinterpret casts
    • 5.50.4 Blackfin Built-in Functions
    • 5.50.5 FR-V Built-in Functions
      • 5.50.5.1 Argument Types
      • 5.50.5.2 Directly-mapped Integer Functions
      • 5.50.5.3 Directly-mapped Media Functions
      • 5.50.5.4 Raw read/write Functions
      • 5.50.5.5 Other Built-in Functions
    • 5.50.6 X86 Built-in Functions
    • 5.50.7 MIPS DSP Built-in Functions
    • 5.50.8 MIPS Paired-Single Support
    • 5.50.9 MIPS Loongson Built-in Functions
      • 5.50.9.1 Paired-Single Arithmetic
      • 5.50.9.2 Paired-Single Built-in Functions
      • 5.50.9.3 MIPS-3D Built-in Functions
    • 5.50.10 picoChip Built-in Functions
    • 5.50.11 Other MIPS Built-in Functions
    • 5.50.12 PowerPC AltiVec Built-in Functions
    • 5.50.13 SPARC VIS Built-in Functions
    • 5.50.14 SPU Built-in Functions
  • 5.51 Format Checks Specific to Particular Target Machines
    • 5.51.1 Solaris Format Checks
  • 5.52 Pragmas Accepted by GCC
    • 5.52.1 ARM Pragmas
    • 5.52.2 M32C Pragmas
    • 5.52.3 RS/6000 and PowerPC Pragmas
    • 5.52.4 Darwin Pragmas
    • 5.52.5 Solaris Pragmas
    • 5.52.6 Symbol-Renaming Pragmas
    • 5.52.7 Structure-Packing Pragmas
    • 5.52.8 Weak Pragmas
    • 5.52.9 Diagnostic Pragmas
    • 5.52.10 Visibility Pragmas
    • 5.52.11 Push/Pop Macro Pragmas
    • 5.52.12 Function Specific Option Pragmas
  • 5.53 Unnamed struct/union fields within structs/unions
  • 5.54 Thread-Local Storage
    • 5.54.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage
    • 5.54.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
  • 5.55 Binary constants using the `0b' prefix
• 6 Extensions to the C++ Language
  • 6.1 When is a Volatile Object Accessed?
  • 6.2 Restricting Pointer Aliasing
  • 6.3 Vague Linkage
  • 6.4 #pragma interface and implementation
  • 6.5 Where's the Template?
  • 6.6 Extracting the function pointer from a bound pointer to member function
  • 6.7 C++-Specific Variable, Function, and Type Attributes
  • 6.8 Namespace Association
  • 6.9 Type Traits
  • 6.10 Java Exceptions
  • 6.11 Deprecated Features
  • 6.12 Backwards Compatibility
• 7 GNU Objective-C runtime features
  • 7.1 +load: Executing code before main
    • 7.1.1 What you can and what you cannot do in +load
  • 7.2 Type encoding
  • 7.3 Garbage Collection
  • 7.4 Constant string objects
  • 7.5 compatibility_alias
• 8 Binary Compatibility
• 9 gcov—a Test Coverage Program
  • 9.1 Introduction to gcov
  • 9.2 Invoking gcov
  • 9.3 Using gcov with GCC Optimization
  • 9.4 Brief description of gcov data files
  • 9.5 Data file relocation to support cross-profiling
• 10 Known Causes of Trouble with GCC
  • 10.1 Actual Bugs We Haven't Fixed Yet
  • 10.2 Cross-Compiler Problems
  • 10.3 Interoperation
  • 10.4 Incompatibilities of GCC
  • 10.5 Fixed Header Files
  • 10.6 Standard Libraries
  • 10.7 Disappointments and Misunderstandings
  • 10.8 Common Misunderstandings with GNU C++
    • 10.8.1 Declare and Define Static Members
    • 10.8.2 Name lookup, templates, and accessing members of base classes
    • 10.8.3 Temporaries May Vanish Before You Expect
    • 10.8.4 Implicit Copy-Assignment for Virtual Bases
  • 10.9 Caveats of using protoize
  • 10.10 Certain Changes We Don't Want to Make
  • 10.11 Warning Messages and Error Messages
• 11 Reporting Bugs
  • 11.1 Have You Found a Bug?
  • 11.2 How and where to Report Bugs
• 12 How To Get Help with GCC
• 13 Contributing to GCC Development
• Funding Free Software
• The GNU Project and GNU/Linux
• GNU General Public License
• GNU Free Documentation License
  • ADDENDUM: How to use this License for your documents
• Contributors to GCC
• Option Index
• Keyword Index

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