My introduction to "##"

Todd_s02

I was never one for the intricacies of the C preprocessor. On my latest project, apparently (or rather, unfortunately) someone is. An .h file has a bunch of definitions (real variable names changed to protect the innocent): statedefs.h: makeState(State1, 0x01) makeState(State2, 0x02) makeState(State3, 0x03) Odd, I think, but ok. Then I go look up "makeState". What the... 3 entries? That's not a good sign. Instance 1: #define makeState(NAME, NUM) ST_##NAME## = ##NUM##, typedef enum { #include "statedefs.h" ST_LAST } statetype; Instance 2: Embedded in the middle of a function(!) #undef makestate #define makeState(NAME, NUM) somevariable++; #include "statedefs.h" Instance 3: #define makestate(NAME, NUM) { "ST_"#NAME,0,0}, sometype stateinfo[] = { #include "statedefs.h" } There are no external programs being used, no weird autogeneration stuff.. the entire set of code is a replacement for: enum { ST_State1 = 1, ST_State2 = 2, ST_State3 = 3, ST_LAST } Most editors I've tried cannot tag it, due to the preprocessor concatenation used ("##" in instance 1). References don't work either. And this is one of the easier to read examples of preprocessor abuse... I just try and remind myself that code written this way makes it that much easier on my next job interview!

Michael Dunn

#define makeState(NAME, NUM) ST_##NAME## = ##NUM##,

:wtf: To add insult to, well, insult - he only needed the first ##. Maybe he thought the macro params needed to be "quoted" with ## ?

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ Ford, what's this fish doing in my ear?

Pete OHanlon

That's somebody trying to be clever just to show off. I'm a great believer in the KISS principle, and this person deserves to be severely slapped with a wet haddock.

Deja View - the feeling that you've seen this post before.

Marcus J Smith

Pete O`Hanlon wrote:

KISS

Yeah I wish people would remember that...dangit!

CleaKO

"I think you'll be okay here, they have a thin candy shell. 'Surprised you didn't know that.'" - Tommy (Tommy Boy)
"Fill it up again! Fill it up again! Once it hits your lips, it's so good!" - Frank the Tank (Old School)

Tristan Rhodes

KISS - 1) Lots of small, primitive working components that perform a specific task and clip together? 2) Few large complex classes? Which one? [Edit: Typo - Simple = Complex in 2nd option]

------------------------------- Carrier Bags - 21st Century Tumbleweed.

peterchen

somestateinfo gives you literal strings for the names, so it's a replacement for:

enum
{
ST_State1 = 1,
ST_State2 = 2,
ST_State3 = 3,

ST_LAST
}

sometype stateinfo[] =
{
{ "ST_State1", 0, 0 },
{ "ST_State2", 0, 0 },
{ "ST_State2", 0, 0 },
}

If he'd used, say, #define makestate(NAME, NUM) { "ST_"#NAME,NUM,0}, you could derive a name-value mapping for enums. It could even remove a prefix from the enum constant. The "inside a function" counts the values actually defined, which would be better derived from sizeof(stateinfo)/sizeof(stateinfo[0]) Not that I ever endorse such conding practices :rolleyes: But it's a not-to-unusual way around lack of reflection in C / C++.

We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
My first real C# project | Linkify!|FoldWithUs! | sighist

PIEBALDconsult

I'm just trying to figure out how I'd do this. I never liked having an enum and a separate string array that had to be kept in sync. I learned some more about the "C preprocessor" today. More reason to like C#

peterchen

I think the best thing would be an Excel sheet (or similar) and a code generator that is included in the build process.

We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
My first real C# project | Linkify!|FoldWithUs! | sighist

peterchen

You got something here! At a certain point, complexity can be moved around between "participants", but it remains in the project. "clipping components together" can increase complexity by one (thinking on a logarithmic scale) If your target is, however, still two or three orders of complexity away, you are in trouble. I think the idea is to plug together the next layer's "small, primitive classes" from the layer below. However, plugging components may give you the robustness of an application, but components have much higher requirements to be pluggable. At each layer, you spend more and more glue code to fit things together. It helps to start with a "more skilled", higher level language (i.e. start at higher complexity already, so the gap gets smaller), or apply KISS to the project goals (but that's not always possible). Hmmm... no solution, nope.

We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
My first real C# project | Linkify!|FoldWithUs! | sighist

Pete OHanlon

Complexity does not necessarily contradict the KISS principle. Many problems are complex, but the constituent parts to the solution should be as simple as possible to solve the problem.

Deja View - the feeling that you've seen this post before.

PIEBALDconsult

I'm now pondering storing the values in XML and using XSLT to create the h file. XSLT: the new C Preprocessor

Dan Neely

that'd be worthy of a fresh thread here in and of itself.

-- CleaKO The sad part about this instance is that none of the users ever said anything [about the problem]. Pete O`Hanlon Doesn't that just tell you everything you need to know about users?

peterchen

I actually wanted to do that as a project to "learn XML", but just the basics were such a bumpy ride that I contracted some kind of XML allergy. So if you do: A R T I C L E ! ;)

We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
My first real C# project | Linkify!|FoldWithUs! | sighist

PIEBALDconsult

Correct you are, but should I? Or should it go in, perhaps, the XML/XSL forum? Or an article? Aw heck, here it is, you decide: state.xml

state.xsl

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" >
<xsl:output omit-xml-declaration="yes" method="text"/>
<xsl:template match="/">
<xsl:for-each select="*">
typedef enum {
<xsl:for-each select="*">
<xsl:value-of select="../@Prefix"/><xsl:value-of select="name()"/>=<xsl:value-of select="."/>,
<xsl:if test="position()=last()"><xsl:value-of select="../@Prefix"/>LAST=<xsl:value-of select="last()"/></xsl:if>
</xsl:for-each>} <xsl:value-of select="name()"/>type ;
<xsl:value-of select="@Type"/>xsl:text </xsl:text><xsl:value-of select="name()"/>info[] = {
<xsl:for-each select="*">
<xsl:if test="position()!=1">,</xsl:if>{"<xsl:value-of select="../@Prefix"/><xsl:value-of select="name()"/>",0,0}
</xsl:for-each>}
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>

result

  typedef enum {
  ST\_State1=0x01,
    ST\_State2=0x02,
    ST\_State3=0x03,
    ST\_LAST=3} statetype ;
  sometype stateinfo\[\] = {
  {"ST\_State1",0,0}
  ,{"ST\_State2",0,0}
  ,{"ST\_State3",0,0}
  }

As mentioned elsewhere, the counting of the entries in part two is unnecessary, but notice that here I set the value of ST_LAST to the number of entries.

PIEBALDconsult

Be careful what you ask for.

Dan Neely

I call a WTF!:laugh:

-- CleaKO The sad part about this instance is that none of the users ever said anything [about the problem]. Pete O`Hanlon Doesn't that just tell you everything you need to know about users?

Tristan Rhodes

From my experience, combining the smallest atomic parts together to create another simple atomic part is simply part of good system design. I've encountered HUGE function classes which have masses of dependancies on other stuff and it's a complete nightmare to figure out. At least with lots of small components you can black box at each level and the whole system becomes that much simpler to comprehend. T

------------------------------- Carrier Bags - 21st Century Tumbleweed.

PIEBALDconsult

What's your alternative of choice?

Anton Afanasyev

PIEBALDconsult wrote:

Be careful what you ask for.

I believe this actually is a case where he wants to get what he wishes for..

:badger:

PIEBALDconsult

(He's probably the only one.)