How do you want to call the C function out of Perl? I think you are looking for something like:

SV *
err_msg( code )
    int code;
  INIT:
    char sError[255];
  CODE:
    QAErrorMessage( code, sError, 255 );
    SV *result = newSVpv(sError, 0);
  OUTPUT:
    result
[download]