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Manual Reference Pages  -  FPP (1)


fpp - the Fortran language preprocessor for FORTRAN 77 and Fortran 90.


     Source files
     Macro definition.
     Including External Files.
     Line control.
     Conditional selection of source text.
     Scope of macro or variable definitions.
     End of macro definition
     Function-like macro definition
     Cancelling macro definitions of both kinds
     Conditional source code selection
     Including External Files
     Intrinsic functions
     Macro expansion
See Also


fpp [ options ] [ input-file [ output-file ] ]


fpp is the preprocessor for FORTRAN 77 and Fortran 90. fpp optionally accepts two filenames as arguments. input-file and output-file are, respectively, the input file read and the output file written by the preprocessor. By default standard input and output are used. fpp should be used instead of the cpp preprocessor with the Sun FORTRAN 77 compiler.


  By default, C style comments are recognized. Turn this off by specifying -c_com=no
-Dname Define the preprocessor variable name as 1 (one). This is the same as if a -Dname=1 option appeared on the fpp command line, or as if a
#define name 1
line appeared in the source file, which is processed by fpp.

  Define name as if by a #define directive. This is the same as if a
#define name def
line appeared in the source file that fpp is processing. The -D option has lower precedence than the -U option. That is, if the same name is used in both a -U option and a -D option, the name will be undefined regardless of the order of the options.
-fixed Assumes fixed format input source.
-free Assumes free format input source.
  Insert directory into the search path for #include files with names not beginning with /’. directory is inserted ahead of the standard list of ‘‘include’’ directories. Thus, #include files with names enclosed in double-quotes (") are searched for first in the directory of the file with the #include line, then in directories named with -I options, and lastly, in directories from the standard list. For #include files with names enclosed in angle-brackets (<>), the directory of the file with the #include line is not searched.
-M Generate a list of makefile dependencies and write them to the standard output. This list indicates that the object file which would be generated from the input file depends on the input file as well as the include files referenced.
  By default, macros are expanded everywhere. Turn off macro expansion in comments by specifying -macro=no_com and turn off macro expansion all together by specifying -macro=no
-P Do not put line numbering directives to the output file. This directive appears as #line-number file-name
-Uname Remove any initial definition of name, where name is a fpp variable that is predefined by a particular preprocessor. Here is a partial list of symbols that may be predefined, depending upon the architecture of the system:
Operating System: unix, __unix, and__SVR4
Hardware: sun, __sun, sparc, and__sparc
-undef Remove initial definitions for all predefined symbols.
-w0 Don’t output warnings from fpp to stderr.
-Xu Convert upper-case letters to lower-case, except within character-string constants. The default is to not convert upper-case letters to lower-case.
-Xw For fixed form source files (See below) fpp assumes that the symbol ’ ’ (space) is insignificant. By default for this form the ’space’ symbol is the delimiter of tokens.
  Use the specified directory in place of the standard list of directories when searching for files.
fpp also understands some FORTRAN 77 compiler options (See f77(1)):
-e Accept extended source lines, up to 132 characters long.
-w Do not output warnings to stderr.


    Source files

fpp operates on both fixed and free form source files. Files with ’.F’ extension are assumed to be in fixed form, and files with ’.F90’ extensions (and all others) are assumed to be in free form by default. There is the ’-fixed’ option for using fixed form in Fortran 90. fpp recognizes the tab format of a source line when in fixed mode.

A source file may contain fpp tokens. fpp tokens are close to those of Fortran. They are:

- fpp directive names.
- symbolic names including Fortran keywords. fpp permits all symbols in names that Fortran does.
- constants. Integer, real, double and quadruple precision, binary, octal, hexadecimal including alternate notation, character and hollerith.
- comments. There are Fortran comments and fpp comments.
- others. Special characters, space, tab, newline, etc.


Output consists of a modified copy of the input, plus lines of the form:

#line_number file_name

inserted to indicate the original source line number and filename of the output line that follows. There is the ’-P’ option (See above) which disables the generation of these lines.


Syntax and semantics of fpp directives are the same as cpp directives (See cpp(1)).

All fpp directives start with the hash symbol (#) as the first character on a line. White space (SPACE or TAB characters) can appear after the initial ’#’ for proper indentation. The directives can be divided into the following groups:

- macro definitions;

- conditional source code selection;

- inclusion of external files;

- line control.

    Macro definition.

The #define directive is used to define both simple string variables and more complicated macros:

#define name token-string

This is the definition of a fpp variable. Wherever ’name’ appears in the source lines following the definition, ’token-string’ will be substituted for ’name’.

#define name(argument [, argument] ... ) token-string

This is the definition of a function-like macro. Occurrences of the macro ’name’ followed by the comma-separated list of arguments within parentheses are substituted by the token string produced from the macro definition. Every occurrence of an argument identifier from the macro definition’s arguments list is substituted by the token sequence representing the corresponding macro actual argument.

In these definitions, spaces between the macro name and the ’(’ symbol are prohibited to prevent the directive being interpreted as a fpp variable definition with the rest of the line beginning with the ’(’ symbol being interpreted as a token-string.

#undef name

Remove any definition for ’name’ (produced by ’D’ options, #define directives or by default). No additional tokens are permitted on the directive line after the name.

    Including External Files.

There are two forms of file inclusion:

#include "filename"

#include <filename>

Read in the contents of filename at this location. The lines read in from the file are processed by fpp as if it were a part of the current file.

When the <filename> notation is used, filename is only searched for in the standard ‘‘include’’ directories. See the ’I’ and ’Y’ options above for more detail. No additional tokens are permitted in the directive line after the final ‘"’ or ‘>’.

    Line control.

#line-number "filename"

Generate line control information for the next pass of the compiler. The integer-constant is interpreted as the line number of the next line and the filename is interpreted as the name of the file from where it comes. If "filename" is not given, the current filename is unchanged.

    Conditional selection of source text.

There are two forms of conditional selection of source text

1) #if condition_1
#elif condition_2
2) #ifdef name
#elif condition
or #ifndef name
#elif condition
else- and elif-part are optional. There may be more than one elif-part. Condition is an expression involving fpp constants, macros and intrinsic functions. Condition expressions are similar to cpp expressions, and may contain any cpp operations and operands with the exception of c long, octal and hexadecimal constants. Additionally, fpp will accept and evaluate Fortran logical operations .NOT. .AND. .OR. .EQV. .NEQV. .GT. .LT. .LE. .GE. etc. and logical constants .TRUE. .FALSE.


    Scope of macro or variable definitions.

The scope of a definition begins from the place of its definition and encloses all the source lines (and source lines from included files) from that definition line to the end of the current file.

There are the following exceptions to the scope effected by an fpp definition:

- files included by Fortran INCLUDE statements;

- fpp and Fortran comments;

- IMPLICIT single letter specifications;

- FORMAT specifications;

- numeric, typeless and character constants.

The scope of the macro effect can be limited by means of the #undef directive.

    End of macro definition

Macro definition can be of any length and is limited only by the ’newline’ symbol. A Macro can be defined in multiple lines. A Macro can be continued to the next line with the insertion of ’\’. So, the occurrence of a ’newline’ without a macro-continuation signifies the end of the macro definition.

For example:
#define long_macro_name(x,\
y) x*y

    Function-like macro definition

The number of macro call arguments should be the same as the number of arguments in the corresponding macro definition. An error is flagged if they don’t.

    Cancelling macro definitions of both kinds

#undef name

After this directive, ’name’ would not interpreted by fpp as a macro or variable name. If this name has not been defined earlier as a macro name, then the given directive has no effect

    Conditional source code selection

- Constant-expression

Subsequent lines up to the matching #else, #elif, or #endif directive, appear in the output only if their constant-expression yields a true value.

The lines following the #elif directive appear in the output only if all of the following conditions hold:

- The constant-expression in the preceding #if directive evaluated to .FALSE. or the name in the preceding #ifdef directive is not defined or the name in the preceding #ifndef directive is defined.
- The constant-expression in all intervening #elif directives evaluated to .FALSE.
- The current constant-expression evaluates to .TRUE.

If the constant-expression evaluates to .TRUE., subsequent #elif and #else directives are ignored up to the matching #endif. Any constant-expression allowed in an #if directive is allowed in an #elif directive.

The intrinsic function ‘defined’ can be used in a constant-expression also.

The following items are permitted:

- C language operations: <, >, ==, !=, >=, <=, +, -, /, *, %, <<, >>, &, ~, |, &&, || They are interpreted by fpp in accordance to the C language semantics (this facility is provided for compatibility with "old" Fortran programs using cpp)
- Fortran language operations: .AND., .OR., .NEQV., .XOR., .EQV., .NOT. , .GT., .LT., .LE., .GE., .NE., .EQ., ** (power).
- Fortran logical constants: .TRUE. , .FALSE.
Only these items, integer constants, and names can be used within a constant-expression. Names which have not been defined with the help of the ’D’ option, a #define directive or by default, get 0 as the value. The C operation ’!=’ (not equal) can be used in #if or #elif directive, but NOT in #define directive, where the symbol ’!’ is considered as the Fortran comment symbol.
#ifdef name
  Subsequent lines up to the matching #else, #elif, or #endif appear in the output only if the name has been defined, either by a #define directive or by the ’D’ option, and in the absence of an intervening #undef directive. No additional tokens are permitted on the directive line after name.
#ifndef name
  Subsequent lines up to the matching #else, #elif, or #endif appear in the output only if name has not been defined, or if its definition has been removed with an #undef directive. No additional tokens are permitted on the directive line after name.
#elif constant-expression .
  Any number of #elif directives may appear between an #if, #ifdef, or #ifndef directive and a matching #else or #endif directive.
#else This inverts the sense of the conditional directive otherwise in effect. If the preceding conditional would indicate that lines are to be included, then lines between the #else and the matching #endif are ignored. If the preceding conditional indicates that lines would be ignored, subsequent lines are included in the output. Conditional directives and corresponding #else directives can be nested.
#endif End a section of lines begun by one of the conditional directives #if, #ifdef, or #ifndef. Each such directive must have a matching #endif.

    Including External Files

Is the same as it is for cpp. Files are searched as follows:

for #include "file_name":

- in the directory, in which the processed file has been found;
- in the directories specified by the -I option;
- in the default directory.

for #include <file_name>:

- in the directories specified by the -I option;
- in the default directory.

fpp directives (beginning with the # symbol in the first position of lines) can be placed anywhere in a source code, in particular before a Fortran continuation line. The only exception is the prohibition of fpp directives within a macro call divided on several lines by means of continuation symbols.


fpp permits comments of two kinds:

1) Fortran language comments. A source line containing one of the symbols ’C’, ’c’, ’*’, ’d’ or ’D’ in the first position, is considered as a comment line. Within such lines macro expansions are not performed. The ’!’ symbol is interpreted as the beginning of a comment extending to the end of the line. The only exception is the case when this symbol occurs within a constant-expression in #if and #elif directives (See above).

2) fpp comments enclosed in the ’/*’ and ’*/’ parasymbols. They are excluded from the output and macro expansions are not performed within these symbols. fpp comments can be nested and for each parasymbol ’/*’ there must be a corresponding parasymbol ’*/’. fpp comments are suitable for excluding the compilation of large portions of source instead of commenting every line with Fortran comment symbols.

    Intrinsic functions

The intrinsic function

defined(name) or defined name


.TRUE. - if name is defined as a macro.

.FALSE.- if the name is not defined.

    Macro expansion

If, during expansion of a macro, the column width of a line exceeds column 72 (for the fixed format) or column 132 (for the free format), fpp inserts appropriate continuation lines.

In the fixed form there is limitation on macro expansions in label fields (positions 1-5):

- a macro call (together with possible arguments) should not extend more than the column 5 position;
- a macro call whose name begins with one of the Fortran comment symbols is considered as a part of a comment;
- a macro expansion may produce a text extending beyond the column 5 position. In such a case a warning will be issued.

In the fixed form when the ’-Xw’ option has been specified an ambiguity may appear if a macro call occurs in a statement position and a macro name begins or coincides with a Fortran keyword. For example, in the following text:

#define callp(x) call f(x)
call p(0)

fpp can not determine with certainty how to interpret the ’call p’ token sequence. It could be considered as a macro name. The current implementation does the following:

- the longer identifier is chosen (callp in this case);
- from this identifier the longest macro name or keyword is extracted;
- if a macro name has been extracted a macro expansion is performed. If the name begins with some keyword fpp outputs an appropriate warning;
- the rest of the identifier is considered as a whole identifier.

In the above example the macro expansion would be performed and the following warning would be output:

warning: possibly incorrect substitution of macro callp

It should be noted that this situation appears only when preprocessing a fixed format source code and when the space symbol is not interpreted as a token delimiter. It should be said also that if a macro name coincides with a keyword beginning part, as in the following case:

#define INT INTEGER*8

then in accordance with the described algorithm, the INTEGER keyword will be found earlier than the INT macro name. Thus, there will be no warning when preprocessing such a macro definition.


There are three kinds of diagnostic messages:

- warnings. preprocessing of source code is continued and the return value remains to be 0.
- errors. fpp continues preprocessing but sets the return code to a nonzero value, namely number of errors.
- fatal error. fpp cancels preprocessing and returns a nonzero return value.

The messages produced by fpp are intended to be self-explanatory. The line number and filename where the error occurred are printed along with the diagnostic.


cpp(1), f77(1), f90(1)

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