preprocessor: how to operate on strings

**red floyd** · Apr 11 '08, 05:35 AM

Re: preprocessor: how to operate on strings

abir wrote:

Hi,
This is not strictly a C++ language question.
Is there any way to form a string from an identifier with the
preprocessor with some operations ?
>
i.e to say to make a string from an identifier ID i use #ID.
Thats ok, but what if i want to alter it a little.
>
like if i have an identifier myID , and i want to generate an string
MYID (or any other form) from it.
I am also interested to know if it can be done using template also ,
i.e myID -myID (string, using preprocessor) -MYID (using
template) .
>
I am interested in a compile time solution, runtime one is trivial.
>

read up on the ## token pasting operator.

#define MY(id) my ## id

MY(Word) // generates myWord
MY(Goodness) // generates myGoodness

**abir** · Apr 11 '08, 05:55 AM

Re: preprocessor: how to operate on strings

On Apr 11, 10:34 am, red floyd <no.s...@here.d udewrote:

abir wrote:

Hi,
This is not strictly a C++ language question.
Is there any way to form a string from an identifier with the
preprocessor with some operations ?

>

i.e to say to make a string from an identifier ID i use #ID.
Thats ok, but what if i want to alter it a little.

>

like if i have an identifier myID , and i want to generate an string
MYID (or any other form) from it.
I am also interested to know if it can be done using template also ,
i.e myID -myID (string, using preprocessor) -MYID (using
template) .

>

I am interested in a compile time solution, runtime one is trivial.

>
read up on the ## token pasting operator.
>
#define MY(id) my ## id
>
MY(Word) // generates myWord
MY(Goodness) // generates myGoodness

Thats true, but i have an identifier myID, and not id. So i can't do
that.
to clarify the point, say i have an enum
enum MyEnum{
meType1,meType2
};
i want to make a few strings from it as TYPE1, TYPE2 , where the input
is meType1, meType2 and NOT anything else (which will be done using
some seq preprocessor constructs from boost) .
So to say, i want to apply some construct statically of meType1 to
generate TYPE1 either using preprocessor or using template.

thanks
abir

**James Kanze** · Apr 11 '08, 10:15 AM

Re: preprocessor: how to operate on strings

On Apr 11, 7:48 am, abir <abirba...@gmai l.comwrote:

On Apr 11, 10:34 am, red floyd <no.s...@here.d udewrote:

abir wrote:

This is not strictly a C++ language question.
Is there any way to form a string from an identifier with the
preprocessor with some operations ?

i.e to say to make a string from an identifier ID i use #ID.
Thats ok, but what if i want to alter it a little.

like if i have an identifier myID , and i want to generate an string
MYID (or any other form) from it.
I am also interested to know if it can be done using template also ,
i.e myID -myID (string, using preprocessor) -MYID (using
template) .

I am interested in a compile time solution, runtime one is trivial.

read up on the ## token pasting operator.

#define MY(id) my ## id

MY(Word) // generates myWord
MY(Goodness) // generates myGoodness

Thats true, but i have an identifier myID, and not id. So i can't do
that.
to clarify the point, say i have an enum
enum MyEnum{
meType1,meType2 };

i want to make a few strings from it as TYPE1, TYPE2 , where
the input is meType1, meType2 and NOT anything else (which
will be done using some seq preprocessor constructs from
boost) .

You can't, really. You have two choices: either write a small
parser yourself (e.g. ignoring everything but enum's), and use
it to generate the strings, or write a small program which
generates both the enum and the strings from some simply
formatted input. I've done the first, and it's not that hard.
And in your case, the second would only be about 10 lines of GNU
awk. (Standard awk doesn't have a toupper function, so you'd
have to implement that as well.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

**Ben Bacarisse** · Apr 11 '08, 12:55 PM

Re: preprocessor: how to operate on strings

abir <abirbasak@gmai l.comwrites:
<snip>

Thats true, but i have an identifier myID, and not id. So i can't do
that.
to clarify the point, say i have an enum
enum MyEnum{
meType1,meType2
};
i want to make a few strings from it as TYPE1, TYPE2 , where the input
is meType1, meType2 and NOT anything else (which will be done using
some seq preprocessor constructs from boost) .
So to say, i want to apply some construct statically of meType1 to
generate TYPE1 either using preprocessor or using template.

You might consider using an extra pre-processor step. M4 (a
general-purpose macro processor) can be told to use sufficiently
obscure syntax that it is unlikely to mess with any of your C++ but
will pick out exactly those bits where you want to do this sort of
transformation.

--
Ben.

**Robbie Hatley** · Apr 11 '08, 08:55 PM

Re: preprocessor: how to operate on strings

"abir" asked:

This is not strictly a C++ language question.

It's on-topic, though. The preprocessor is a part of C++.

Is there any way to form a string from an identifier with the
preprocessor with some operations ?

Some really nifty things can be done with the preprocessor.
I used the following to cut several hundred messy lines of
error-prone cut-n-paste code down to about a dozen lines in
the program I'm maintaining here at work:

#define AUXI_ITEM(r,t,c ) IG ## r ## _ ## t ## c

The "##" directive is a "string paster".
This macro builds a string out of 3 input strings (t, r, c).
It just pastes together "IG", r, "_", t, c.

For example, the preprocessor would convert

AUXI_ITEM ( 07 , AgQm , 3375 )

to:

IG07_AgQm3375

--
Cheers,
Robbie Hatley
lonewolf aatt well dott com
www dott well dott com slant user slant lonewolf slant

**Ben Bacarisse** · Apr 11 '08, 10:55 PM

Re: preprocessor: how to operate on strings

"Robbie Hatley" <see.my.signatu re@for.my.email .addresswrites:

"abir" asked:
>

>This is not strictly a C++ language question.

>
It's on-topic, though. The preprocessor is a part of C++.
>

>Is there any way to form a string from an identifier with the
>preprocessor with some operations ?

>
Some really nifty things can be done with the preprocessor.
I used the following to cut several hundred messy lines of
error-prone cut-n-paste code down to about a dozen lines in
the program I'm maintaining here at work:
>
#define AUXI_ITEM(r,t,c ) IG ## r ## _ ## t ## c
>
The "##" directive is a "string paster".

Small point: it is usually called a token paster. # is the one that
turns a macro argument into a string literal.

This macro builds a string out of 3 input strings (t, r, c).

Really, it builds a token out 3 other tokens. I know you know this.
I just think it help to keep the terminology clear.

It just pastes together "IG", r, "_", t, c.
>
For example, the preprocessor would convert
>
AUXI_ITEM ( 07 , AgQm , 3375 )
>
to:
>
IG07_AgQm3375

--
Ben.

**James Kanze** · Jun 27 '08, 04:34 PM

Re: preprocessor: how to operate on strings

On Apr 11, 7:48 am, abir <abirba...@gmai l.comwrote:

On Apr 11, 10:34 am, red floyd <no.s...@here.d udewrote:

abir wrote:

This is not strictly a C++ language question.
Is there any way to form a string from an identifier with the
preprocessor with some operations ?

i.e to say to make a string from an identifier ID i use #ID.
Thats ok, but what if i want to alter it a little.

like if i have an identifier myID , and i want to generate an string
MYID (or any other form) from it.
I am also interested to know if it can be done using template also ,
i.e myID -myID (string, using preprocessor) -MYID (using
template) .

I am interested in a compile time solution, runtime one is trivial.

read up on the ## token pasting operator.

#define MY(id) my ## id

MY(Word) // generates myWord
MY(Goodness) // generates myGoodness

Thats true, but i have an identifier myID, and not id. So i can't do
that.
to clarify the point, say i have an enum
enum MyEnum{
meType1,meType2 };

i want to make a few strings from it as TYPE1, TYPE2 , where
the input is meType1, meType2 and NOT anything else (which
will be done using some seq preprocessor constructs from
boost) .

You can't, really. You have two choices: either write a small
parser yourself (e.g. ignoring everything but enum's), and use
it to generate the strings, or write a small program which
generates both the enum and the strings from some simply
formatted input. I've done the first, and it's not that hard.
And in your case, the second would only be about 10 lines of GNU
awk. (Standard awk doesn't have a toupper function, so you'd
have to implement that as well.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

**Ben Bacarisse** · Jun 27 '08, 04:34 PM

Re: preprocessor: how to operate on strings

abir <abirbasak@gmai l.comwrites:
<snip>

Thats true, but i have an identifier myID, and not id. So i can't do
that.
to clarify the point, say i have an enum
enum MyEnum{
meType1,meType2
};
i want to make a few strings from it as TYPE1, TYPE2 , where the input
is meType1, meType2 and NOT anything else (which will be done using
some seq preprocessor constructs from boost) .
So to say, i want to apply some construct statically of meType1 to
generate TYPE1 either using preprocessor or using template.

You might consider using an extra pre-processor step. M4 (a
general-purpose macro processor) can be told to use sufficiently
obscure syntax that it is unlikely to mess with any of your C++ but
will pick out exactly those bits where you want to do this sort of
transformation.

--
Ben.

**Robbie Hatley** · Jun 27 '08, 04:34 PM

Re: preprocessor: how to operate on strings

"abir" asked:

This is not strictly a C++ language question.

It's on-topic, though. The preprocessor is a part of C++.

Is there any way to form a string from an identifier with the
preprocessor with some operations ?

Some really nifty things can be done with the preprocessor.
I used the following to cut several hundred messy lines of
error-prone cut-n-paste code down to about a dozen lines in
the program I'm maintaining here at work:

#define AUXI_ITEM(r,t,c ) IG ## r ## _ ## t ## c

The "##" directive is a "string paster".
This macro builds a string out of 3 input strings (t, r, c).
It just pastes together "IG", r, "_", t, c.

For example, the preprocessor would convert

AUXI_ITEM ( 07 , AgQm , 3375 )

to:

IG07_AgQm3375

--
Cheers,
Robbie Hatley
lonewolf aatt well dott com
www dott well dott com slant user slant lonewolf slant

**Ben Bacarisse** · Jun 27 '08, 04:34 PM

Re: preprocessor: how to operate on strings

"Robbie Hatley" <see.my.signatu re@for.my.email .addresswrites:

"abir" asked:
>

>This is not strictly a C++ language question.

>
It's on-topic, though. The preprocessor is a part of C++.
>

>Is there any way to form a string from an identifier with the
>preprocessor with some operations ?

>
Some really nifty things can be done with the preprocessor.
I used the following to cut several hundred messy lines of
error-prone cut-n-paste code down to about a dozen lines in
the program I'm maintaining here at work:
>
#define AUXI_ITEM(r,t,c ) IG ## r ## _ ## t ## c
>
The "##" directive is a "string paster".

Small point: it is usually called a token paster. # is the one that
turns a macro argument into a string literal.

This macro builds a string out of 3 input strings (t, r, c).

Really, it builds a token out 3 other tokens. I know you know this.
I just think it help to keep the terminology clear.

It just pastes together "IG", r, "_", t, c.
>
For example, the preprocessor would convert
>
AUXI_ITEM ( 07 , AgQm , 3375 )
>
to:
>
IG07_AgQm3375

--
Ben.

preprocessor: how to operate on strings

preprocessor: how to operate on strings

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment