Using fpp Directives

Directives for string substitution

fpp contains directives that result in substitutions in a user's program:

Directive for inclusion of external files

There are two forms of file inclusion:

#include "filename"

#include <filename>

This directive reads in the contents of the named file into this location in the source. The lines read in from the file are processed by fpp just as if they were part of the current file.

When the <filename> notation is used, filename is only searched for in the standard "include" directories. See the fpp -I and the -Y options in Using Fortran Preprocessor Options. No additional tokens are allowed on the directive line after the final '"' or ">".

Files are searched for in the following order:

• for #include "filename":

  • in the directory in which the source file resides

  • in the directories specified by the -I or -Y option

  • in the default directory

• for #include <filename>:

  • in the directories specified by the -I or -Y option

  • in the default directory

Directive for line control

This directive takes the following form:

#line-number "filename"

This directive generates line control information for the Fortran compiler. line-number is an integer constant that is the line number of the next line. "filename" is the name of the file containing the line. If "filename" is not provided, the current filename is assumed.

Directive for fpp variable and macro definitions

The #define directive, used to define both simple string variables and more complicated macros, takes the two forms.

The first form is the definition of an fpp variable:

 #define name token-string

In the above, occurrences of name in the source file will be substituted with token-string.

The second form is the definition of an fpp macro.

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

In the above, occurrences of the macro name followed by the comma-separated list of actual arguments within parentheses are replaced by token-string with each occurrence of each argument in token-string replaced by the token sequence representing the corresponding "actual" argument in the macro call.

An error is produced if the number of macro call arguments is not the same as the number of arguments in the corresponding macro definition. For example, consider this macro definition:

#define INTSUB(m, n, o) call mysub(m, n, o)

Any use of the macro INTSUB must have three arguments. In macro definitions, spaces between the macro name and the open parenthesis "(" are prohibited to prevent the directive from being interpreted as an fpp variable definition with the rest of the line beginning with the open parenthesis "(" being interpreted as its token-string.

An fpp variable or macro definition can be of any length and is limited only by the newline symbol. It can be defined in multiple lines by continuing it to the next line with the insertion of "\". The occurrence of a newline without a macro-continuation signifies the end of the macro definition.

Example:

#define long_macro_name(x,\
   y) x*y

The scope of a definition begins from the #define and encloses all the source lines (and source lines from #include files) to the end of the current file, except for:

• files included by Fortran INCLUDE statements

• fpp and Fortran comments

• Fortran IMPLICIT statements that specify a single letter

• Fortran FORMAT statements

• numeric, typeless, and character constants

Directive for undefining a macro

This directive takes the following form:

#undef name

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

If name has not been defined earlier, then the #undef directive has no effect.

Directive for macro expansion

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

For fixed format, there is a limit on macro expansions in label fields (positions 1-5):

• a macro call (together with possible arguments) should not extend beyond column 5

• a macro call whose name begins with one of the Fortran comment symbols is considered to be part of a comment

• a macro expansion may produce text extending beyond column 5. In this case, a warning will be issued

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

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

fpp cannot determine how to interpret the "call p" token sequence above. 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 issues an appropriate warning

• the rest of the identifier is considered as a whole identifier

In the previous example, the macro expansion is performed and the following warning is produced:

warning: possibly incorrect substitution of macro callp

This situation appears only when preprocessing a fixed format source code and when the space symbol is not interpreted as a token delimiter.

In the following case, a macro name coincides with a beginning of a keyword:

 #define INT  INTEGER*8
              INTEGER k

The INTEGER keyword will be found earlier than the INT macro name. There will be no warning when preprocessing such a macro definition.

Directives for conditional selection of source text

There are three forms of conditional selection of source text.

Form 1:

#if condition_1
block_1
#elif condition_2
block_2
#elif ...
#else
block_n
#endif

Form 2:

#ifdefname
block_1
#elif condition
block_2
#elif ...
#else
block_n
#endif

Form 3:

#ifndef name
block_1
#elif condition
block_2
#elif ...
#else
block_n
#endif

The #elif and #else parts are optional in all three forms. There can be more than one #elif part in each form.

Conditional expressions

condition_1, condition_2, etc. are logical expressions involving fpp constants, macros, and intrinsic functions. 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.

• the fpp intrinsic function "defined": defined(name) or defined name which returns .TRUE. if name is defined as an fpp variable or a macro or returns .FALSE. if the name is not defined

#ifdef is a shorthand for #if defined(name) and #ifndef is a shorthand for #if .not. defined(name).

Only these items, integer constants, and names can be used within a constant-expression. A name that has not been defined with the -D option, a #define directive, or by default, has a value of 0. The C operation != (not equal) can be used in the #if or #elif directive, but not in the #define directive, where the symbol ! is considered to be the Fortran comment symbol by default.

Conditional constructs

The following table summarizes conditional constructs.