As of version 0.6, WebFortran's Command Line Interface includes a simple preprocessor similar to those provided by other Fortran and C compilers. Unlike some other preprocessors, this system will accept strings passed with either single or double quotes, similar to the Fortran language itself. For example, the following #define directives are equivalent:

#define MYNAME    "Margaux"
#define MYNAME    'Margaux'

This structure allows the embedding of quotes within a string simply by using the opposite set:

#define QUOTATION '"Good morning," Henry said.'

Supported Directives

WebFortran only supports the following directives:

Directive Description
#define LABEL [value]Define LABEL in the preprocessor, optionally to the value passed
#elsePaired with an #if, #ifdef, or #ifndef, perform processing using the opposite of the condition
#endifPaired with an #if, #ifdef, #ifndef, and/or #else, close the condition and proceed with processing based on any earlier conditions
#error [message]Immediately raise an error during preprocessing, printing the message if specified
#if EXPRESSIONIf EXPRESSION resolves as true, process the contents until an #else or #endif are encountered (See below for EXPRESSION details)
#ifdef LABELIf LABEL is defined, process the contents until an #else or #endif are encountered
#ifndef LABELIf LABEL is defined, do not process the contents until an #else or #endif are encountered
#include "FILE"Open the specified file at the filename FILE based on any compiler flags dictating search locations and include its contents in the current file, continuing with preprocessing said FILE's contents as well
#undef LABELUndefine LABEL in the preprocessor

Predefined Values

WebFortran, by default, defines the following:

Label Description
__FILE__The current file name (without path) being preprocessed
__GFORTRAN__Because WebFortran relies on a GNU Fortran backend, this label is defined, though not set to a sensible value
__LINE__The current line number in the file being preprocessed
__WEBFORTRAN__Indicates the WebFortran compiler is being used


The #if directive can resolve simple expressions revolving around "defined" state of macros. These expressions can combine logical operators and parentheses with the defined(LABEL) operation for more complex barriers. For example, to check if both __WEBFORTRAN__ and WINDOWS are defined, one would write:

#if defined(__WEBFORTRAN__) && defined(WINDOWS)

Because WebFortran is a Fortran compiler first and foremost, it will also accept Fortran-style logical operators:

#if defined(__WEBFORTRAN__) .and. defined(WINDOWS)

The following operators are supported:

Operator Description
!, .not. Logical NOT
&&, .and. Logical AND
||, .or. Logical OR
true, .true. Resolves to true in an expression, but nowhere else in the preprocessor
false, .false. Resolves to false in an expression, but nowhere else in the preprocessor

At this time, WebFortran does not support any arithmetic, numeric comaprisons, or macro replacement within expressions.


The WebFortran preprocessor will not follow Fortran INCLUDE statements when processing source files, though it does follow #include directives. The INCLUDE statement is part of the Fortran language, which is always processed after the preprocessor.

All preprocessing is handled locally before passing the processed source to the server's compiler. Users should therefore not assume that the entire GNU C preprocessor is available.

Functional macros, which would accept arguments and generate replacement code, are not supported at this time.

Any defined LABEL encountered during preprocessing that reside inside comments or strings are ignored.