Chapter 15, The preprocessor

It currently works similar to old C preprocessors but has a few extra features. This chapter describes the different preprocessor directives. This is what it can do:

DIRECTIVE

#!

DESCRIPTION

This directive is in effect a comment statement, since the preprocessor will ignore everything to the end of the line. This is used to write Unix type scripts in Pike by starting the script with

DIRECTIVE

#""

DESCRIPTION

Makes it possible to write strings with newline in them.

#"Foo
bar"

is the same as

"Foo\nbar"

DIRECTIVE

#define

DESCRIPTION

The simplest way to use define is to write

BUGS

Note that it is not a good idea to do something like this:

EXAMPLE

#define A "test"
#define B 17
#define C(X) (X)+(B)+"\n"
#define W write
#define Z Stdio.stdout
int main()
{
    Z->W(C(A));
}

DIRECTIVE

#undef

DESCRIPTION

This removes the effect of a #define, all subsequent occurrences of the undefined identifier will not be replaced by anything. Note that when undefining a macro, you just give the identifier, not the arguments.

EXAMPLES

#define foo bar
#undef foo
#define foo(bar) gazonk bar
#undef foo

DIRECTIVE

#if
#elif
#elseif
#else
#endif

DESCRIPTION

The #if directive causes conditional compiling of code depending on the expression after the #if directive. That is, if the expression is true, the code up to the next #else, #elif, #elseif or #endif is compiled. If the expression is false, that code will be skipped. If the skip leads up to a #else, the code after the else will be compiled. #elif and #elseif are equivalent and causes the code that follow them to be compiled if the previous #if or #elif evaluated false and the expression after the #elif evaluates true.

EXAMPLES

#if 1

#else

#endif

#elif defined(BAR)

#else

#endif

DIRECTIVE

#error

DESCRIPTION

This directive causes a compiler error, it can be used to notify the user that certain functions are missing and similar things.

EXAMPLES

#if !constant(write_file)
#error write_file function is missing
#endif

DIRECTIVE

#include

DESCRIPTION

This directive should be given a file as argument, it will then be compiled as if all those lines were written at the #include line. The compiler then continues to compile this file.

EXAMPLES

#include "foo.h"

DIRECTIVE

#line

DESCRIPTION

This directive tells the compiler what line and file we are compiling. This is for instance used by the #include directive to tell the compiler that we are compiling another file. The directive takes the line number first, and optionally, the file afterwards.

EXAMPLES

#line 4 "foo.cf" /* The next line was generated from 4 in foo.cf */

DIRECTIVE

#pragma

DESCRIPTION

This is a generic directive for flags to the compiler. Currently, the only flag available is 'all_inline' which is the same as adding the modifier 'inline' to all functions that follows.

DIRECTIVE

#string

DESCRIPTION

This directive works as #include but makes the included file a string.

string html_doc=#string "index.html";

This puts the file index.html into the string html_doc.