So, for example, almost all of Fortran 95 code is valid Fortran 90 code. In fact, fixed-form source is still valid even in the Fortran standard although only a lunatic would write object-oriented code in fixed-form format.
To sum up:. Stop the madness, or we're really going to be in trouble 75 years from now. May 16, Fortran File Extensions Part of the confusion about modern Fortran is what file extension to use.
This attribute applies to the pointer association status, not to the target of the pointer. Note that when setting the lower bound of any rank in a pointer assignment, the values must be explicitly specified there is no default of 1 like there is in array declarators and they must be specified for all dimensions of the pointer.
Note that when rank-remapping, the values for both the lower and upper bounds must be explicitly specified for all dimensions, there are no defaults. This is shown in the table below. Furthermore, the Fortran object cannot be polymorphic, a zero-sized array, an assumed-size array, or an array pointer. Note that in all the conversion cases it is up to the programmer to use the correct type and other information.
Again, the C name is for use only from C, the Fortran name is used from Fortran. If the C name is all blanks or a zero-length string , there is no C name. Such a procedure can still be called from C via a procedure pointer i. Each dummy argument must be a variable whose type corresponds to a C type, and cannot be allocatable, assumed-shape, optional or a pointer.
The kind used for a particular set of enumerators can be discovered by using the KIND intrinsic on one of the enumerators. Thus each procedure starts with the flags clear, and when it returns any flag that is set will cause the corresponding flag in the caller to become set.
This ensures that procedures that can be executed in parallel will not interfere with each other via the IEEE exception flags. This enables code motion optimisations within all routines, and the only cost is that procedures which modify the modes must restore them to the state on entry when they return.
The modes that are available are: separately, whether each floating point exception terminates the program or allows execution to continue providing a default result and raising an exception flag ; rounding mode for floating-point operations; underflow mode.
Those feature types which are required by the user procedure should be explicitly referenced by the USE statement with an ONLY clause, e. The following predefined constants are provided. This gradually reduces the precision of the numbers as they get closer to zero: the smallest number has only one bit of precision, so any calculation with such a number will have a very large relative error.
Its main advantage is that it can be much faster. A stream file is either a formatted stream or an unformatted stream. A formatted stream file is equivalent to a C text stream; this acts much like an ordinary sequential file, except that there is no limit on the length of a record. Just as in C, when writing to a formatted stream, an embedded newline character in the data causes a new record to be created.
Data written to an unformatted stream is transferred to the file with no formatting, and data read from an unformatted stream is transferred directly to the variable as it appears in the file.
The first character of the file is at position 1. Note that unlike unformatted sequential files, writing to an unformatted stream file at a position earlier than the end of the file does not truncate the file. However, this truncation does happen for formatted streams. This takes a scalar default character variable, which in the event of an error is assigned an explanatory message. If no error occurs, the value of the variable remains unchanged.
Furthermore, the output is right-justified within the output field. For list-directed output the output field is the minimum size to hold the result. Input of IEEE infinities and NaNs is now possible; these take the same form as the output described above, except that: case is not significant, a NaN may be preceded by a sign, which is ignored, and a NaN may be followed by alphanumeric characters enclosed in parentheses the NAG Fortran Compiler also ignores these.
The Fortran 90 and 95 standards both specified E format. Note that an allocatable variable that appears in a namelist group must be allocated, and a pointer variable that appears in a namelist group must be associated, when a READ or WRITE statement with that namelist is executed. In the OPEN statement, this specifier determines whether asynchronous data transfer is allowed for that file: the default setting is 'NO'.
After initiating an asynchronous data transfer, the variables affected must not be referenced or defined until after the transfer is known to have finished. For an asynchronous WRITE of a local variable, this means not returning from the procedure until after ensuring the transfer is complete. An asynchronous data transfer is known to have been finished if there is a subsequent synchronous data transfer, an INQUIRE statement which returns.
This is adequate for asynchronous data transfers that initiate and complete within a single procedure. Both of these restrictions apply whether the attribute was given explicitly or implicitly. It has the form WAIT wait-spec [ , wait-spec ] On completion of execution of the WAIT statement the specified asynchronous data transfers have been completed. Here is an example of using the WAIT statement. REAL array ,,10 ,xferid 10! This trivial extension was part of Fortran 66 that was removed in Fortran 77, and reinstated in Fortran The iomsg argument must be left alone if no error occurred, and must be assigned an explanatory message if iostat is set to a nonzero value.
The vlist argument contains the list of values in the DT edit descriptor if present, and is otherwise a zero-sized array. Note that the syntax of the DT edit descriptor is: DT [ character-literal ] [ value [ , value ] No file positioning commands are permitted. If unit is associated with an external file i. The name of an abstract interface can be used in the procedure declaration statement to declare a specifc procedure with that interface, e.
The procedure declaration statement can also be used with the name of any procedure that has an explicit interface, e. The following attributes can be declared at the same time on the procedure declaration statement: BIND C A non-intrinsic module is the normal kind of module i.
If these are not used, the compiler will select an intrinsic module only if no user-defined module is found. Note that this is only available for user-defined operator names; the intrinsic operators.
This allows expressions to be more readable when array constructors are being mixed with ordinary parentheses. The default value for std is gnu , which specifies a superset of the latest Fortran standard that includes all of the extensions supported by GNU Fortran, although warnings will be given for obsolete extensions not recommended for use in new code.
The legacy value is equivalent but without the warnings for obsolete extensions, and may be useful for old non-standard programs. The f95 , f , f , and f values specify strict conformance to the Fortran 95, Fortran , Fortran and Fortran standards, respectively; errors are given for all extensions beyond the relevant language standard, and warnings are given for the Fortran 77 features that are permitted but obsolescent in later standards.
Note that, with a few exceptions, the fortran standards are highly backwards-compatable, so that much "nice", standard conforming, fortran code is also valid fortran code. The main problem with that is that much fortran code from the 80s and earlier is neither "nice" nor standard-conforming. Some other compilers don't recognize. And do you really want to rename your files when a new standard comes out?
The main difference is the source layout that the compiler will expect: free form for. Upper-case filetypes will cause the preprocessor to be run. You can force fixed-form layout with the options -ffixed-form -ffixed-line-length-none. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How can gfortran tell if I am compiling f90 or f95 code? Ask Question. Asked 9 years, 7 months ago.
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