Re: fread not working -- C400-L


On 17/03/2005, at 4:56 AM, James Rich wrote:

I wrote (well copied from someone else) a little C program that does this:
int
main (int argc, char *argv[])
{
  FILE *infile;
  char buffer[LEN_BUF + 1];
  int len = LEN_BUF;
  infile = fopen ("/home/james/test.ps", "rb");
  len = fread (buffer, sizeof (char), LEN_BUF, infile);
  fclose (infile);
  return 0;
}
When I compile it with *IFSIO everything works just fine. But I need to make this part of an RPG program. So I change int main(int argc, char *argv[]) to int copy_ps_to_sf(FILE *infile), remove the FILE *infile declaration from the body of the function, and used CRTCMOD with *IFSIO. My RPG program opens the file and passes the file pointer as 10I 0. But now when this function runs I get:
read(): Operation not supported.
from perror. How can I read a file in C that I opened in RPG?

You should be able to do this but you must ensure you are using the same operations in RPG and C.

You say RPG is passing a 'file pointer' as 10I 0? That's not a pointer. It is a descriptor which suggests you are using the open() function in RPG. Note that the C example is using fopen() which does return a pointer (hence the * in the definition of FILE * infile; They ain't the same thing.

You cannot use fread() to process a file opened with open() because one uses descriptors and the other uses a pointer to a FILE structure. You can convert a descriptor to a FILE structure using the fdopen() function and then use fread(). See the C Runtime Library Reference for specific details--especially how to close the file if fdopen() fails.

You have a few choices: a) Convert the descriptor to a FILE using fdopen() before issuing fread() b) Modify the C example to use descriptor I/O. Change fread() to read() and fclose() to close(). Note that the parameters for the descriptor-based functions are different from the FILE-base functions so you'll need to alter them c) Modify your RPG to use fopen() and pass the FILE pointer to C

Regards,
Simon Coulter.
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