PCALL LOG(LOGLVL : %STR(LOGTXT))

Books on this subject:
RPG IV Jump Start : Moving Ahead With the New RPG

Is LOGTXT defined as a character field, or as a basing pointer?

It sounds like it's defined as a character field.

If so, try this (not properly aligned!)

D LogTxt             S      20A  Based(LogTxtPtr)
D LogTxtPtr          S        *

then use %Str(LogTxtPtr)

Hope this helps.
Gary Guthrie Editor, The RPG Source Technical Editor, NEWS/400 magazine

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Another thing that might work, but wouldn't be as elegant as the pointer solution, would be to concatenate an X'00 (Hex 00 - Null) to the end of the string

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On your prototype define your second parameter with the keyword Options(*String) and then use the built-in-function %TrimR to call your procedure like this:

CALLP LOG(LOGLVL : %TRIMR(LOGTXT))

Here's another example:

Dperror           PR            10I 0 ExtProc( 'perror' )
D                                 *   Value  Options( *String )

C                   Eval      RC       =  perror( %TrimR( FileNam ))

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YES ! That works.
Hurray, I've written my 'hello world' program in RPG :

     D txt             S             40A   INZ('Hello, world !')

     D log             PR                  EXTPROC('logit')
     D    txt                          *   VALUE OPTIONS(*STRING)

     C                   CALLP     log(%TRIMR(txt))
     C                   RETURN

And the C module linked to this is simply

void logit (char *t)
{
  printf("'%s'\n", t);
}

Thanks for the solution.

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Are you sure the RPG compiler you use has the same release level as the manual? There are many enhancements to RPGLE between OS/400 3.2 and 4.2. If your compiler is old many of the other suggestions I read so far will also fail to work. In that case, using %trimr() and appending a x'00' manually is your only solution.

Also, you cannot write your own str() function in rpg or C, unless you also pass the length of the character field, or know the length of the character field in advance. Since you want to find the last non-blank character, you have to start looking at the end of the character string, and the compiler has no way of finding out, unless you either pass fixed-length fields, or pass the length as a parameter.

It would be a great idea though, if the rpg compiler writers gave us a macro or template facility, so that we could write our own functions, which would look like procedure calls, but would be able to handle arbitrary parameter variable lengths, just like the built in functions. Right now prototyped functions cannot handle parameters of different storage size very well.

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They can if they are character variables, but not numeric ones. You need to code the prototype with Options(*Varsize) which causes the compiler to pass "operational descriptors" along with the parameter.

The function then must do a call to CEEDOD to obtain the size of the expression or variable passed. This allows you to do implement this type of function even in V3R2 on CISC machines.

Unfortunately operational descriptors are not available for numeric variables so we don't have a good way of knowing length and decimal positions, which makes it hard to implement a %editc() look-alike.

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Check out the new (V4R2) keyword VARYING available to variables & parameters in RPG/IV. Once the length is set (using %Len or %TrimR where appropriate), the program keeps track of it.

Passing procedure parameters this way you won't have to check the actual length, the program will know what storage to access (and what not to).

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Me thinks this does it:

.
.
.
  *
  *    Determine input parameter lenght for procedure parameter.
  *
 C                   CALLP     CEEDOD(1         : DescType : DataType :
 C                                    DescInfo1 : DescInfo2: InLen    :
 C                                    *OMIT)
  *
 C     ' '           check     CenterString  LeftByte
  *
 C                   EVAL      WrkString =
 C                               %subst(CenterString:LeftByte:
 C                                      InLen - LeftByte + 1)
  *
 C                   EVAL      NbrofChar = %LEN(%trim(WrkString))
  *
 C                   IF        NbrofChar 

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Found it now.... It's because I use TGTRLS(V3R2M0). Leave that out
and it works. Probbaly %STR was introduced after 3.2. Drat !
Thanks all for pointing me in the right direction syntactically.

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