Call RPGLE from a C program

[d7d1cd_]

Hey. I have a service program in RPGLE that has a procedure that returns a value (10 characters). Can someone explain how to declare this procedure in a C program to get the return value?

[Scott Klement]

Normally, C will only pass character strings by reference (i.e. a pointer is passed.) However, you can work around this with a struct or typedef. Is that what you're asking? Can you provide a copy of the RPG prototype so we can see the specifics you are referring to?

[d7d1cd_]

Scott, you probably misunderstood me. I need to call a procedure in C code, which is in a service program written in RPG. Here is a synthetic example of a procedure in a service program:

     D SomeFoo         pr            10    EXTPROC('SomeFoo')
     D   param1                      10A   const


     PSomeFoo          B                   export
     DSomeFoo          pi            10
     D   param1                      10A   const
      *
     C                   clear                   ret              10
     C                   movel     'Text from'   ret
     C     param1        dsply
     C                   return    ret
     C
     pSomeFoo          e

And this is a C program in which a procedure from a service program is called and in which I need to get what the procedure returns:

char* SomeFoo(char*);

int main()
{
  char* ptr;
  ptr = SomeFoo("asdfg     "); // Here ptr doesn't get any meaning
}

In this example, in C, the service program works, since when the SomeFoo procedure is called, the line passed in the procedure parameter appears in the job log. However, I cannot get the information that the procedure returns to me.

[d7d1cd_]

Scott, you probably misunderstood me. I need to call a procedure in C code, which is in a service program written in RPG. Here is a synthetic example of a procedure in a service program:

     D SomeFoo         pr            10    EXTPROC('SomeFoo')
     D   param1                      10A   const


     PSomeFoo          B                   export
     DSomeFoo          pi            10
     D   param1                      10A   const
      *
     C                   clear                   ret              10
     C                   movel     'Text from'   ret
     C     param1        dsply
     C                   return    ret
     C
     pSomeFoo          e

And this is a C program in which a procedure from a service program is called and in which I need to get what the procedure returns:

char* SomeFoo(char*);

int main()
{
  char* ptr;
  ptr = SomeFoo("asdfg     "); // Here ptr doesn't get any meaning
}

In this example, in C, the service program works, since when the SomeFoo procedure is called, the line passed in the procedure parameter appears in the job log. However, I cannot get the information that the procedure returns to me.

[Scott Klement]

So... I've already explained to you why that code sample won't work!

While C expects strings as a pointer, RPG does not. So you can't assign a pointer to the return value because the RPG is NOT returning a pointer. Change your C prototype to use a struct or typedef.

[Scott Klement]

Here's an example:

#include <stdio.h>

typedef struct _RPG_Char10_t {
  char data[10];
} RPG_Char10_t;

RPG_Char10_t SomeFoo(char *param1);

int main()
{
  RPG_Char10_t ret;
  ret = SomeFoo("asdfg     ");
  printf("%10.10s\n", ret.data);
}

[d7d1cd_]

Scott, thank you very much! It works now!