How do I generate code like for using a C macro? #for?-CodePudding

Is there are C macro like the for loop, that can generate code for me to use functions?

for example:

I have

SetSystem1();
SetSystem2();
SetSystem3();
...
SetSystem100();

can I write

#for index = 0 to 100
    SetSystem##index();
#endfor

so the system will generate SetSystem1 to SetSystem100?

Is there are some macro can create code like this?

I can't use array pointer to the C library.

CodePudding user response：

Is there are some macro can create code like this?

No, not really. Even if you want to create such macro, you have to spell out all possibilities - it will take 100 macros for 100 cases.

You can use libraries that come with such maros, like p99 https://gustedt.gitlabpages.inria.fr/p99/p99-html/group__preprocessor__for_gae3eb0e3a5216300874ed6cb9abc170ce.html#gae3eb0e3a5216300874ed6cb9abc170ce :

#define P00_SEP(NAME, I, REC, RES) REC; RES
#define P00_VASSIGN(NAME, X, I)  SetSystem##I()
P99_FOR(A, 101, P00_SEP, P00_VASSIGN, , );

Or boost https://www.boost.org/doc/libs/1_78_0/libs/preprocessor/doc/index.html :

#define DECL(z, I, text) SetSystem##I();
BOOST_PP_REPEAT_FROM_TO(1, 100, DECL, )

You can also use some external preprocessor additionally to C preprocessor. For example with m4:

# forloop.m4, from documentation
divert(`-1')
# forloop(var, from, to, stmt)
define(`forloop',
  `pushdef(`$1', `$2')_forloop(`$1', `$2', `$3', `$4')popdef(`$1')')
define(`_forloop',
  `$4`'ifelse($1, `$3', ,
    `define(`$1', incr($1))_forloop(`$1', `$2', `$3', `$4')')')
divert`'dnl

forloop(`i', `1', `100', `dnl
`      SetSystem'i`();
'')

or with php:

<?php for ($i = 1; $i <= 100; $i  ) echo "SystemOut".$i."();\n"; ?>

or with Python Jinja2:

{% for i in range(1, 100) %}
      SystemOut{{ i }}();
{% endfor %}

CodePudding user response：

There is no such facility in the C preprocessor. Given the complexity of this tool and its shortcomings, there is no chance that it be extended in future versions of the C Standard.

You can use another tool to generate the text and include that in your source file. Here is an example using the bash shell:

for i in {1..100} ; do echo "    SetSystem$i();" ; done

Alternately, using the tr utility:

echo "SetSystem"{1..100}"();" | tr ' ' '\n'

Or as commented by Eric Postpischil, using jot on BSD systems:

jot -w '    SetSystem%d();' 100

But KamilCuk found a simpler and most elegant solution:

printf "    SetSystem%d();\n" {1..100}

Advanced programmers' editors have powerful macro systems that will enable you to produce the same output interactively.