The GNU Fortran Compiler

Table of Contents

• Introduction
• 1 Introduction
  • 1.1 About GNU Fortran
  • 1.2 GNU Fortran and GCC
  • 1.3 Preprocessing and conditional compilation
  • 1.4 GNU Fortran and G77
  • 1.5 Project Status
  • 1.6 Standards
    • 1.6.1 Varying Length Character Strings
• 2 GNU Fortran Command Options
  • 2.1 Option summary
  • 2.2 Options controlling Fortran dialect
  • 2.3 Enable and customize preprocessing
  • 2.4 Options to request or suppress errors and warnings
  • 2.5 Options for debugging your program or GNU Fortran
  • 2.6 Options for directory search
  • 2.7 Influencing the linking step
  • 2.8 Influencing runtime behavior
  • 2.9 Options for code generation conventions
  • 2.10 Environment variables affecting gfortran
• 3 Runtime: Influencing runtime behavior with environment variables
  • 3.1 TMPDIR—Directory for scratch files
  • 3.2 GFORTRAN_STDIN_UNIT—Unit number for standard input
  • 3.3 GFORTRAN_STDOUT_UNIT—Unit number for standard output
  • 3.4 GFORTRAN_STDERR_UNIT—Unit number for standard error
  • 3.5 GFORTRAN_UNBUFFERED_ALL—Do not buffer I/O on all units
  • 3.6 GFORTRAN_UNBUFFERED_PRECONNECTED—Do not buffer I/O on preconnected units
  • 3.7 GFORTRAN_SHOW_LOCUS—Show location for runtime errors
  • 3.8 GFORTRAN_OPTIONAL_PLUS—Print leading + where permitted
  • 3.9 GFORTRAN_DEFAULT_RECL—Default record length for new files
  • 3.10 GFORTRAN_LIST_SEPARATOR—Separator for list output
  • 3.11 GFORTRAN_CONVERT_UNIT—Set endianness for unformatted I/O
  • 3.12 GFORTRAN_ERROR_BACKTRACE—Show backtrace on run-time errors
• 4 Fortran 2003 and 2008 Status
  • 4.1 Fortran 2003 status
  • 4.2 Fortran 2008 status
  • 4.3 Technical Specification 29113 Status
• 5 Compiler Characteristics
  • 5.1 KIND Type Parameters
  • 5.2 Internal representation of LOGICAL variables
  • 5.3 Thread-safety of the runtime library
  • 5.4 Data consistency and durability
  • 5.5 Files opened without an explicit ACTION= specifier
• 6 Extensions
  • 6.1 Extensions implemented in GNU Fortran
    • 6.1.1 Old-style kind specifications
    • 6.1.2 Old-style variable initialization
    • 6.1.3 Extensions to namelist
    • 6.1.4 X format descriptor without count field
    • 6.1.5 Commas in FORMAT specifications
    • 6.1.6 Missing period in FORMAT specifications
    • 6.1.7 I/O item lists
    • 6.1.8 Q exponent-letter
    • 6.1.9 BOZ literal constants
    • 6.1.10 Real array indices
    • 6.1.11 Unary operators
    • 6.1.12 Implicitly convert LOGICAL and INTEGER values
    • 6.1.13 Hollerith constants support
    • 6.1.14 Cray pointers
    • 6.1.15 CONVERT specifier
    • 6.1.16 OpenMP
    • 6.1.17 OpenACC
    • 6.1.18 Argument list functions %VAL, %REF and %LOC
    • 6.1.19 Read/Write after EOF marker
  • 6.2 Extensions not implemented in GNU Fortran
    • 6.2.1 STRUCTURE and RECORD
    • 6.2.2 ENCODE and DECODE statements
    • 6.2.3 Variable FORMAT expressions
    • 6.2.4 Alternate complex function syntax
    • 6.2.5 Volatile COMMON blocks
• 7 Mixed-Language Programming
  • 7.1 Interoperability with C
    • 7.1.1 Intrinsic Types
    • 7.1.2 Derived Types and struct
    • 7.1.3 Interoperable Global Variables
    • 7.1.4 Interoperable Subroutines and Functions
    • 7.1.5 Working with Pointers
    • 7.1.6 Further Interoperability of Fortran with C
  • 7.2 GNU Fortran Compiler Directives
  • 7.3 Non-Fortran Main Program
    • 7.3.1 _gfortran_set_args — Save command-line arguments
    • 7.3.2 _gfortran_set_options — Set library option flags
    • 7.3.3 _gfortran_set_convert — Set endian conversion
    • 7.3.4 _gfortran_set_record_marker — Set length of record markers
    • 7.3.5 _gfortran_set_fpe — Enable floating point exception traps
    • 7.3.6 _gfortran_set_max_subrecord_length — Set subrecord length
  • 7.4 Naming and argument-passing conventions
    • 7.4.1 Naming conventions
    • 7.4.2 Argument passing conventions
• 8 Coarray Programming
  • 8.1 Type and enum ABI Documentation
    • 8.1.1 caf_token_t
    • 8.1.2 caf_register_t
  • 8.2 Function ABI Documentation
    • 8.2.1 _gfortran_caf_init — Initialiation function
    • 8.2.2 _gfortran_caf_finish — Finalization function
    • 8.2.3 _gfortran_caf_this_image — Querying the image number
    • 8.2.4 _gfortran_caf_num_images — Querying the maximal number of images
    • 8.2.5 _gfortran_caf_register — Registering coarrays
    • 8.2.6 _gfortran_caf_deregister — Deregistering coarrays
    • 8.2.7 _gfortran_caf_send — Sending data from a local image to a remote image
    • 8.2.8 _gfortran_caf_get — Getting data from a remote image
    • 8.2.9 _gfortran_caf_sendget — Sending data between remote images
    • 8.2.10 _gfortran_caf_lock — Locking a lock variable
    • 8.2.11 _gfortran_caf_lock — Unlocking a lock variable
    • 8.2.12 _gfortran_caf_event_post — Post an event
    • 8.2.13 _gfortran_caf_event_wait — Wait that an event occurred
    • 8.2.14 _gfortran_caf_event_query — Query event count
    • 8.2.15 _gfortran_caf_sync_all — All-image barrier
    • 8.2.16 _gfortran_caf_sync_images — Barrier for selected images
    • 8.2.17 _gfortran_caf_sync_memory — Wait for completion of segment-memory operations
    • 8.2.18 _gfortran_caf_error_stop — Error termination with exit code
    • 8.2.19 _gfortran_caf_error_stop_str — Error termination with string
    • 8.2.20 _gfortran_caf_atomic_define — Atomic variable assignment
    • 8.2.21 _gfortran_caf_atomic_ref — Atomic variable reference
    • 8.2.22 _gfortran_caf_atomic_cas — Atomic compare and swap
    • 8.2.23 _gfortran_caf_atomic_op — Atomic operation
    • 8.2.24 _gfortran_caf_co_broadcast — Sending data to all images
    • 8.2.25 _gfortran_caf_co_max — Collective maximum reduction
    • 8.2.26 _gfortran_caf_co_min — Collective minimum reduction
    • 8.2.27 _gfortran_caf_co_sum — Collective summing reduction
    • 8.2.28 _gfortran_caf_co_reduce — Generic collective reduction
• 9 Intrinsic Procedures
  • 9.1 Introduction to intrinsic procedures
  • 9.2 ABORT — Abort the program
  • 9.3 ABS — Absolute value
  • 9.4 ACCESS — Checks file access modes
  • 9.5 ACHAR — Character in ASCII collating sequence
  • 9.6 ACOS — Arccosine function
  • 9.7 ACOSH — Inverse hyperbolic cosine function
  • 9.8 ADJUSTL — Left adjust a string
  • 9.9 ADJUSTR — Right adjust a string
  • 9.10 AIMAG — Imaginary part of complex number
  • 9.11 AINT — Truncate to a whole number
  • 9.12 ALARM — Execute a routine after a given delay
  • 9.13 ALL — All values in MASK along DIM are true
  • 9.14 ALLOCATED — Status of an allocatable entity
  • 9.15 AND — Bitwise logical AND
  • 9.16 ANINT — Nearest whole number
  • 9.17 ANY — Any value in MASK along DIM is true
  • 9.18 ASIN — Arcsine function
  • 9.19 ASINH — Inverse hyperbolic sine function
  • 9.20 ASSOCIATED — Status of a pointer or pointer/target pair
  • 9.21 ATAN — Arctangent function
  • 9.22 ATAN2 — Arctangent function
  • 9.23 ATANH — Inverse hyperbolic tangent function
  • 9.24 ATOMIC_ADD — Atomic ADD operation
  • 9.25 ATOMIC_AND — Atomic bitwise AND operation
  • 9.26 ATOMIC_CAS — Atomic compare and swap
  • 9.27 ATOMIC_DEFINE — Setting a variable atomically
  • 9.28 ATOMIC_FETCH_ADD — Atomic ADD operation with prior fetch
  • 9.29 ATOMIC_FETCH_AND — Atomic bitwise AND operation with prior fetch
  • 9.30 ATOMIC_FETCH_OR — Atomic bitwise OR operation with prior fetch
  • 9.31 ATOMIC_FETCH_XOR — Atomic bitwise XOR operation with prior fetch
  • 9.32 ATOMIC_OR — Atomic bitwise OR operation
  • 9.33 ATOMIC_REF — Obtaining the value of a variable atomically
  • 9.34 ATOMIC_XOR — Atomic bitwise OR operation
  • 9.35 BACKTRACE — Show a backtrace
  • 9.36 BESSEL_J0 — Bessel function of the first kind of order 0
  • 9.37 BESSEL_J1 — Bessel function of the first kind of order 1
  • 9.38 BESSEL_JN — Bessel function of the first kind
  • 9.39 BESSEL_Y0 — Bessel function of the second kind of order 0
  • 9.40 BESSEL_Y1 — Bessel function of the second kind of order 1
  • 9.41 BESSEL_YN — Bessel function of the second kind
  • 9.42 BGE — Bitwise greater than or equal to
  • 9.43 BGT — Bitwise greater than
  • 9.44 BIT_SIZE — Bit size inquiry function
  • 9.45 BLE — Bitwise less than or equal to
  • 9.46 BLT — Bitwise less than
  • 9.47 BTEST — Bit test function
  • 9.48 C_ASSOCIATED — Status of a C pointer
  • 9.49 C_F_POINTER — Convert C into Fortran pointer
  • 9.50 C_F_PROCPOINTER — Convert C into Fortran procedure pointer
  • 9.51 C_FUNLOC — Obtain the C address of a procedure
  • 9.52 C_LOC — Obtain the C address of an object
  • 9.53 C_SIZEOF — Size in bytes of an expression
  • 9.54 CEILING — Integer ceiling function
  • 9.55 CHAR — Character conversion function
  • 9.56 CHDIR — Change working directory
  • 9.57 CHMOD — Change access permissions of files
  • 9.58 CMPLX — Complex conversion function
  • 9.59 CO_BROADCAST — Copy a value to all images the current set of images
  • 9.60 CO_MAX — Maximal value on the current set of images
  • 9.61 CO_MIN — Minimal value on the current set of images
  • 9.62 CO_REDUCE — Reduction of values on the current set of images
  • 9.63 CO_SUM — Sum of values on the current set of images
  • 9.64 COMMAND_ARGUMENT_COUNT — Get number of command line arguments
  • 9.65 COMPILER_OPTIONS — Options passed to the compiler
  • 9.66 COMPILER_VERSION — Compiler version string
  • 9.67 COMPLEX — Complex conversion function
  • 9.68 CONJG — Complex conjugate function
  • 9.69 COS — Cosine function
  • 9.70 COSH — Hyperbolic cosine function
  • 9.71 COUNT — Count function
  • 9.72 CPU_TIME — CPU elapsed time in seconds
  • 9.73 CSHIFT — Circular shift elements of an array
  • 9.74 CTIME — Convert a time into a string
  • 9.75 DATE_AND_TIME — Date and time subroutine
  • 9.76 DBLE — Double conversion function
  • 9.77 DCMPLX — Double complex conversion function
  • 9.78 DIGITS — Significant binary digits function
  • 9.79 DIM — Positive difference
  • 9.80 DOT_PRODUCT — Dot product function
  • 9.81 DPROD — Double product function
  • 9.82 DREAL — Double real part function
  • 9.83 DSHIFTL — Combined left shift
  • 9.84 DSHIFTR — Combined right shift
  • 9.85 DTIME — Execution time subroutine (or function)
  • 9.86 EOSHIFT — End-off shift elements of an array
  • 9.87 EPSILON — Epsilon function
  • 9.88 ERF — Error function
  • 9.89 ERFC — Error function
  • 9.90 ERFC_SCALED — Error function
  • 9.91 ETIME — Execution time subroutine (or function)
  • 9.92 EXECUTE_COMMAND_LINE — Execute a shell command
  • 9.93 EXIT — Exit the program with status.
  • 9.94 EXP — Exponential function
  • 9.95 EXPONENT — Exponent function
  • 9.96 EXTENDS_TYPE_OF — Query dynamic type for extension
  • 9.97 FDATE — Get the current time as a string
  • 9.98 FGET — Read a single character in stream mode from stdin
  • 9.99 FGETC — Read a single character in stream mode
  • 9.100 FLOOR — Integer floor function
  • 9.101 FLUSH — Flush I/O unit(s)
  • 9.102 FNUM — File number function
  • 9.103 FPUT — Write a single character in stream mode to stdout
  • 9.104 FPUTC — Write a single character in stream mode
  • 9.105 FRACTION — Fractional part of the model representation
  • 9.106 FREE — Frees memory
  • 9.107 FSEEK — Low level file positioning subroutine
  • 9.108 FSTAT — Get file status
  • 9.109 FTELL — Current stream position
  • 9.110 GAMMA — Gamma function
  • 9.111 GERROR — Get last system error message
  • 9.112 GETARG — Get command line arguments
  • 9.113 GET_COMMAND — Get the entire command line
  • 9.114 GET_COMMAND_ARGUMENT — Get command line arguments
  • 9.115 GETCWD — Get current working directory
  • 9.116 GETENV — Get an environmental variable
  • 9.117 GET_ENVIRONMENT_VARIABLE — Get an environmental variable
  • 9.118 GETGID — Group ID function
  • 9.119 GETLOG — Get login name
  • 9.120 GETPID — Process ID function
  • 9.121 GETUID — User ID function
  • 9.122 GMTIME — Convert time to GMT info
  • 9.123 HOSTNM — Get system host name
  • 9.124 HUGE — Largest number of a kind
  • 9.125 HYPOT — Euclidean distance function
  • 9.126 IACHAR — Code in ASCII collating sequence
  • 9.127 IALL — Bitwise AND of array elements
  • 9.128 IAND — Bitwise logical and
  • 9.129 IANY — Bitwise OR of array elements
  • 9.130 IARGC — Get the number of command line arguments
  • 9.131 IBCLR — Clear bit
  • 9.132 IBITS — Bit extraction
  • 9.133 IBSET — Set bit
  • 9.134 ICHAR — Character-to-integer conversion function
  • 9.135 IDATE — Get current local time subroutine (day/month/year)
  • 9.136 IEOR — Bitwise logical exclusive or
  • 9.137 IERRNO — Get the last system error number
  • 9.138 IMAGE_INDEX — Function that converts a cosubscript to an image index
  • 9.139 INDEX — Position of a substring within a string
  • 9.140 INT — Convert to integer type
  • 9.141 INT2 — Convert to 16-bit integer type
  • 9.142 INT8 — Convert to 64-bit integer type
  • 9.143 IOR — Bitwise logical or
  • 9.144 IPARITY — Bitwise XOR of array elements
  • 9.145 IRAND — Integer pseudo-random number
  • 9.146 IS_IOSTAT_END — Test for end-of-file value
  • 9.147 IS_IOSTAT_EOR — Test for end-of-record value
  • 9.148 ISATTY — Whether a unit is a terminal device.
  • 9.149 ISHFT — Shift bits
  • 9.150 ISHFTC — Shift bits circularly
  • 9.151 ISNAN — Test for a NaN
  • 9.152 ITIME — Get current local time subroutine (hour/minutes/seconds)
  • 9.153 KILL — Send a signal to a process
  • 9.154 KIND — Kind of an entity
  • 9.155 LBOUND — Lower dimension bounds of an array
  • 9.156 LCOBOUND — Lower codimension bounds of an array
  • 9.157 LEADZ — Number of leading zero bits of an integer
  • 9.158 LEN — Length of a character entity
  • 9.159 LEN_TRIM — Length of a character entity without trailing blank characters
  • 9.160 LGE — Lexical greater than or equal
  • 9.161 LGT — Lexical greater than
  • 9.162 LINK — Create a hard link
  • 9.163 LLE — Lexical less than or equal
  • 9.164 LLT — Lexical less than
  • 9.165 LNBLNK — Index of the last non-blank character in a string
  • 9.166 LOC — Returns the address of a variable
  • 9.167 LOG — Natural logarithm function
  • 9.168 LOG10 — Base 10 logarithm function
  • 9.169 LOG_GAMMA — Logarithm of the Gamma function
  • 9.170 LOGICAL — Convert to logical type
  • 9.171 LONG — Convert to integer type
  • 9.172 LSHIFT — Left shift bits
  • 9.173 LSTAT — Get file status
  • 9.174 LTIME — Convert time to local time info
  • 9.175 MALLOC — Allocate dynamic memory
  • 9.176 MASKL — Left justified mask
  • 9.177 MASKR — Right justified mask
  • 9.178 MATMUL — matrix multiplication
  • 9.179 MAX — Maximum value of an argument list
  • 9.180 MAXEXPONENT — Maximum exponent of a real kind
  • 9.181 MAXLOC — Location of the maximum value within an array
  • 9.182 MAXVAL — Maximum value of an array
  • 9.183 MCLOCK — Time function
  • 9.184 MCLOCK8 — Time function (64-bit)
  • 9.185 MERGE — Merge variables
  • 9.186 MERGE_BITS — Merge of bits under mask
  • 9.187 MIN — Minimum value of an argument list
  • 9.188 MINEXPONENT — Minimum exponent of a real kind
  • 9.189 MINLOC — Location of the minimum value within an array
  • 9.190 MINVAL — Minimum value of an array
  • 9.191 MOD — Remainder function
  • 9.192 MODULO — Modulo function
  • 9.193 MOVE_ALLOC — Move allocation from one object to another
  • 9.194 MVBITS — Move bits from one integer to another
  • 9.195 NEAREST — Nearest representable number
  • 9.196 NEW_LINE — New line character
  • 9.197 NINT — Nearest whole number
  • 9.198 NORM2 — Euclidean vector norms
  • 9.199 NOT — Logical negation
  • 9.200 NULL — Function that returns an disassociated pointer
  • 9.201 NUM_IMAGES — Function that returns the number of images
  • 9.202 OR — Bitwise logical OR
  • 9.203 PACK — Pack an array into an array of rank one
  • 9.204 PARITY — Reduction with exclusive OR
  • 9.205 PERROR — Print system error message
  • 9.206 POPCNT — Number of bits set
  • 9.207 POPPAR — Parity of the number of bits set
  • 9.208 PRECISION — Decimal precision of a real kind
  • 9.209 PRESENT — Determine whether an optional dummy argument is specified
  • 9.210 PRODUCT — Product of array elements
  • 9.211 RADIX — Base of a model number
  • 9.212 RAN — Real pseudo-random number
  • 9.213 RAND — Real pseudo-random number
  • 9.214 RANDOM_NUMBER — Pseudo-random number
  • 9.215 RANDOM_SEED — Initialize a pseudo-random number sequence
  • 9.216 RANGE — Decimal exponent range
  • 9.217 RANK — Rank of a data object
  • 9.218 REAL — Convert to real type
  • 9.219 RENAME — Rename a file
  • 9.220 REPEAT — Repeated string concatenation
  • 9.221 RESHAPE — Function to reshape an array
  • 9.222 RRSPACING — Reciprocal of the relative spacing
  • 9.223 RSHIFT — Right shift bits
  • 9.224 SAME_TYPE_AS — Query dynamic types for equality
  • 9.225 SCALE — Scale a real value
  • 9.226 SCAN — Scan a string for the presence of a set of characters
  • 9.227 SECNDS — Time function
  • 9.228 SECOND — CPU time function
  • 9.229 SELECTED_CHAR_KIND — Choose character kind
  • 9.230 SELECTED_INT_KIND — Choose integer kind
  • 9.231 SELECTED_REAL_KIND — Choose real kind
  • 9.232 SET_EXPONENT — Set the exponent of the model
  • 9.233 SHAPE — Determine the shape of an array
  • 9.234 SHIFTA — Right shift with fill
  • 9.235 SHIFTL — Left shift
  • 9.236 SHIFTR — Right shift
  • 9.237 SIGN — Sign copying function
  • 9.238 SIGNAL — Signal handling subroutine (or function)
  • 9.239 SIN — Sine function
  • 9.240 SINH — Hyperbolic sine function
  • 9.241 SIZE — Determine the size of an array
  • 9.242 SIZEOF — Size in bytes of an expression
  • 9.243 SLEEP — Sleep for the specified number of seconds
  • 9.244 SPACING — Smallest distance between two numbers of a given type
  • 9.245 SPREAD — Add a dimension to an array
  • 9.246 SQRT — Square-root function
  • 9.247 SRAND — Reinitialize the random number generator
  • 9.248 STAT — Get file status
  • 9.249 STORAGE_SIZE — Storage size in bits
  • 9.250 SUM — Sum of array elements
  • 9.251 SYMLNK — Create a symbolic link
  • 9.252 SYSTEM — Execute a shell command
  • 9.253 SYSTEM_CLOCK — Time function
  • 9.254 TAN — Tangent function
  • 9.255 TANH — Hyperbolic tangent function
  • 9.256 THIS_IMAGE — Function that returns the cosubscript index of this image
  • 9.257 TIME — Time function
  • 9.258 TIME8 — Time function (64-bit)
  • 9.259 TINY — Smallest positive number of a real kind
  • 9.260 TRAILZ — Number of trailing zero bits of an integer
  • 9.261 TRANSFER — Transfer bit patterns
  • 9.262 TRANSPOSE — Transpose an array of rank two
  • 9.263 TRIM — Remove trailing blank characters of a string
  • 9.264 TTYNAM — Get the name of a terminal device.
  • 9.265 UBOUND — Upper dimension bounds of an array
  • 9.266 UCOBOUND — Upper codimension bounds of an array
  • 9.267 UMASK — Set the file creation mask
  • 9.268 UNLINK — Remove a file from the file system
  • 9.269 UNPACK — Unpack an array of rank one into an array
  • 9.270 VERIFY — Scan a string for characters not a given set
  • 9.271 XOR — Bitwise logical exclusive OR
• 10 Intrinsic Modules
  • 10.1 ISO_FORTRAN_ENV
  • 10.2 ISO_C_BINDING
  • 10.3 IEEE modules: IEEE_EXCEPTIONS, IEEE_ARITHMETIC, and IEEE_FEATURES
  • 10.4 OpenMP Modules OMP_LIB and OMP_LIB_KINDS
  • 10.5 OpenACC Module OPENACC
• Contributing
  • Contributors to GNU Fortran
  • Projects
  • Proposed Extensions
    • Compiler extensions:
    • Environment Options
• GNU General Public License
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  • ADDENDUM: How to use this License for your documents
• Funding Free Software
• Option Index
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