12 C++ Applications

No Special Macro Processing

Using C++ with Pro*C/C++ does not require any special preprocessing or special macro processors that are external to Pro*C/C++. There is no need to run a macro processor on the output of the precompiler to achieve C++ compatibility.

If you are a user of a release of Pro*C/C++ Precompiler before this one, and you did use macro processors on the precompiler output, you should be able to precompile your C++ applications using Pro*C/C++ with no changes to your code.

Code Generation

You must be able to specify what kind of code, C compatible code or C++ compatible code, the precompiler generates. Pro*C/C++ by default generates C code. C++ is not a perfect superset of C. Some changes are required in generated code so that it can be compiled by a C++ compiler.

For example, in addition to emitting your application code, the precompiler interposes calls to its runtime library, SQLLIB. The functions in SQLLIB are C functions. There is no special C++ version of SQLLIB. For this reason, if you want to compile the generated code using a C++ compiler, Pro*C/C++ must declare the functions called in SQLLIB as C functions.

For C output, the precompiler would generate a prototype such as

void sqlora(unsigned long *, void *);

But for C++ compatible code, the precompiler must generate

extern "C" {
void sqlora(unsigned long *, void *);
};

You control the kind of code Pro*C/C++ generates using the precompiler option CODE. There are three values for this option: CPP, KR_C, and ANSI_C. The differences between these options can be illustrated by considering how the declaration of the SQLLIB function sqlora differs among the three values for the CODE option:

void sqlora( /*_ unsigned long *, void * _*/);  /* K&R C */

void sqlora(unsigned long *, void *);           /* ANSI C */

extern "C" {                                    /* CPP */
void sqlora(unsigned long *, void *);
};

When you specify CODE=CPP, the precompiler

• Generates C++ compilable code.

• Gives the output file a platform-specific file extension (suffix), such as ".C" or ".cc", rather than the standard ".c" extension. (You can override this by using the CPP_SUFFIX option.)

• Causes the value of the PARSE option to default to PARTIAL. You can also specify PARSE=NONE. If you specify PARSE=FULL, an error is issued at precompile time.

• Allows the use of the C++ style // Comments in your code. This style of Commenting is also permitted inside SQL statements and PL/SQL blocks when CODE=CPP.

• Pro*C/C++ recognizes SQL optimizer hints that begin with //+.

• Requires that header files generated by OTT (Object Type Translator) must be included inside a declare section.

  
  

  See Also: "CODE" for information about the KR_C and ANSI_C values for the CODE option.

  
  

Parsing Code

You must be able to control the effect of the Pro*C/C++ C parser on your code. You do this by using the PARSE precompiler option, which controls how the precompiler's C parser treats your code.

The values and effects of the PARSE option are:

This option value is the default if the value of the CODE option is anything other than CPP. It is an error to specify PARSE=FULL when CODE=CPP.

To generate C++ compatible code, the PARSE option must be either NONE or PARTIAL. If PARSE=FULL, the C parser runs, and it does not understand C++ constructs in your code, such as classes.

Output Filename Extension

Most C compilers expect a default extension of ".c" for their input files. Different C++ compilers, however, can expect different filename extensions. The CPP_SUFFIX option provides the ability to specify the filename extension that the precompiler generates. The value of this option is a string, without the quotes or the period. For example, CPP_SUFFIX=cc, or CPP_SUFFIX=C.

System Header Files

Pro*C/C++ searches for standard system header files, such as stdio.h, in standard locations that are platform specific. Pro*C/C++ does not search for header files with extensions such as hpp or h++. For example, on almost all UNIX systems, the file stdio.h has the full path name /usr/include/stdio.h.

But a C++ compiler has its own version of stdio.h that is not in the standard system location. When you are precompiling for C++, you must use the SYS_INCLUDE precompiler option to specify the directory paths that Pro*C/C++ searches to look for system header files. For example:

SYS_INCLUDE=(/usr/lang/SC2.0.1/include,/usr/lang/SC2.1.1/include)

Use the INCLUDE precompiler option to specify the location of non-system header files. The directories specified by the SYS_INCLUDE option are searched before directories specified by the INCLUDE option. See also: "INCLUDE".

If PARSE=NONE, the values specified in SYS_INCLUDE and INCLUDE for system files are not relevant, since there is no need for Pro*C/C++ to include system header files. (You can, of course, still include Pro*C/C++-specific headers, such sqlca.h, using the EXEC SQL INCLUDE statement.)

cppdemo1.pc

/*  cppdemo1.pc
 *
 *  Prompts the user for an employee number, then queries the 
 *  emp table for the employee's name, salary and commission.
 *  Uses indicator variables (in an indicator struct) to 
 *  determine if the commission is NULL.
 */

#include <iostream.h>
#include <stdio.h>
#include <string.h>

// Parse=partial by default when code=cpp,
// so preprocessor directives are recognized and parsed fully.
#define     UNAME_LEN      20
#define     PWD_LEN        40

// Declare section is required when CODE=CPP or
// PARSE={PARTIAL|NONE} or both.
EXEC SQL BEGIN DECLARE SECTION;
  VARCHAR username[UNAME_LEN];  // VARCHAR is an ORACLE pseudotype
  varchar password[PWD_LEN];    // can be in lower case also

  // Define a host structure for the output values
  // of a SELECT statement
  struct empdat {
      VARCHAR   emp_name[UNAME_LEN];
      float     salary;
      float     commission;
  } emprec;

  // Define an indicator struct to correspond to the
  // host output struct
  struct empind {
      short     emp_name_ind;
      short     sal_ind;
      short     comm_ind;
  } emprec_ind;


  // Input host variables
  int   emp_number;
  int   total_queried;
EXEC SQL END DECLARE SECTION;

// Define a C++ class object to match the desired
// struct from the preceding declare section.
class emp {
  char  ename[UNAME_LEN];
  float salary;
  float commission;
public:
  // Define a constructor for this C++ object that
  // takes ordinary C objects.
  emp(empdat&, empind&);
  friend ostream& operator<<(ostream&, emp&);
};

emp::emp(empdat& dat, empind& ind)
{
  strncpy(ename, (char *)dat.emp_name.arr, dat.emp_name.len);
  ename[dat.emp_name.len] = '\0';
  this->salary = dat.salary;
  this->commission = (ind.comm_ind < 0) ? 0 : dat.commission;
}

ostream& operator<<(ostream& s, emp& e)
{
  return s << e.ename << " earns " << e.salary << 
              " plus " << e.commission << " commission." 
           << endl << endl;
}

// Include the SQL Communications Area
// You can use #include or EXEC SQL INCLUDE
#include <sqlca.h>

// Declare error handling function
void sql_error(char *msg);

main()
{
  char temp_char[32];

  // Register sql_error() as the error handler
  EXEC SQL WHENEVER SQLERROR DO sql_error("ORACLE error:");

  // Connect to ORACLE.  Program calls sql_error()
  // if an error occurs
  // when connecting to the default database.
  // Note the (char *) cast when
  // copying into the VARCHAR array buffer.
  username.len = strlen(strcpy((char *)username.arr, "SCOTT"));
  password.len = strlen(strcpy((char *)password.arr, "TIGER"));
  
  EXEC SQL CONNECT :username IDENTIFIED BY :password;

  // Here again, note the (char *) cast when using VARCHARs
  cout << "\nConnected to ORACLE as user: "
       << (char *)username.arr << endl << endl;

  // Loop, selecting individual employee's results
  total_queried = 0;
  while (1)
  {
      emp_number = 0;
      printf("Enter employee number (0 to quit): ");
      gets(temp_char);
      emp_number = atoi(temp_char);
      if (emp_number == 0)
        break;

      // Branch to the notfound label when the 
      // 1403 ("No data found") condition occurs
      EXEC SQL WHENEVER NOT FOUND GOTO notfound;

      EXEC SQL SELECT ename, sal, comm
         INTO :emprec INDICATOR :emprec_ind // You can also use 
                                            // C++ style
         FROM EMP                  // Comments in SQL statemtents.
         WHERE EMPNO = :emp_number;

      {
        // Basic idea is to pass C objects to
        // C++ constructors thus
        // creating equivalent C++ objects used in the
        // usual C++ way
        emp e(emprec, emprec_ind);
        cout << e;
      }

      total_queried++;
      continue;
notfound:
      cout << "Not a valid employee number - try again." 
           << endl << endl;
  } // end while(1)

  cout << endl << "Total rows returned was " 
       << total_queried << endl;
  cout << "Have a nice day!" << endl << endl;

  // Disconnect from ORACLE
  EXEC SQL COMMIT WORK RELEASE;
  exit(0);
}


void sql_error(char *msg)
{
    EXEC SQL WHENEVER SQLERROR CONTINUE;
    cout << endl << msg << endl;
    cout << sqlca.sqlerrm.sqlerrmc << endl;
    EXEC SQL ROLLBACK RELEASE;
    exit(1);
}

cppdemo2.pc

The next application is a simple modular example. First, execute the following SQL script, cppdemo2.sql, in SQL*Plus:

Rem  This is the SQL script that accompanies the cppdemo2 C++ Demo
Rem  Program.  Run this prior to Precompiling the empclass.pc file.
/
CONNECT SCOTT/TIGER
/
CREATE OR REPLACE VIEW emp_view AS SELECT ename, empno FROM EMP
/
CREATE OR REPLACE PACKAGE emp_package AS
  TYPE emp_cursor_type IS REF CURSOR RETURN emp_view%ROWTYPE;
  PROCEDURE open_cursor(curs IN OUT emp_cursor_type);
END emp_package;
/
CREATE OR REPLACE PACKAGE BODY emp_package AS
  PROCEDURE open_cursor(curs IN OUT emp_cursor_type) IS
  BEGIN
    OPEN curs FOR SELECT ename, empno FROM emp_view ORDER BY ename ASC;
  END;
END emp_package;
/
EXIT
/

The header file empclass.h defines the class emp:

// This class definition may be included in a Pro*C/C++ application
// program using the EXEC SQL INCLUDE directive only.  Because it
// contains EXEC SQL syntax, it may not be included using a #include
// directive.  Any program that includes this header must be
// precompiled with the CODE=CPP option.  This emp class definition
// is used when building the cppdemo2 C++ Demo Program.

class emp
{
  public:
    emp();   // Constructor: ALLOCATE Cursor Variable
    ~emp();  // Desctructor: FREE Cursor Variable

    void open();              // Open Cursor
    void fetch() throw (int); // Fetch (throw NOT FOUND condition)
    void close();             // Close Cursor

    void emp_error();         // Error Handler

    EXEC SQL BEGIN DECLARE SECTION;
      // When included using EXEC SQL INCLUDE, class variables have 
      // global scope and are thus basically treated as ordinary
      // global variables by Pro*C/C++ during precompilation.
      char ename[10];
      int empno;
    EXEC SQL END DECLARE SECTION;

  private:
    EXEC SQL BEGIN DECLARE SECTION;
      // Pro*C/C++ treats this as a simple global variable also.
      SQL_CURSOR emp_cursor;
    EXEC SQL END DECLARE SECTION;
};

The code in empclass.pc contains the emp methods:

#include <stdio.h>
#include <stdlib.h>

// This example uses a single (global) SQLCA that is shared by the
// emp class implementation as well as the main program for this
// application.
#define SQLCA_STORAGE_CLASS extern
#include <sqlca.h>

// Include the emp class specification in the implementation of the
// class body as well as the application program that makes use of it.
EXEC SQL INCLUDE empclass.h;

emp::emp()
{
  // The scope of this WHENEVER statement spans the entire module.
  // Note that the error handler function is really a member function
  // of the emp class.
  EXEC SQL WHENEVER SQLERROR DO emp_error();
  EXEC SQL ALLOCATE :emp_cursor;  // Constructor - ALLOCATE Cursor.
}

emp::~emp()
{
  EXEC SQL FREE :emp_cursor;      // Destructor - FREE Cursor.
}

void emp::open()
{
  EXEC SQL EXECUTE
    BEGIN
      emp_package.open_cursor(:emp_cursor);
    END;
  END-EXEC;
}

void emp::close()
{
  EXEC SQL CLOSE :emp_cursor;
}

void emp::fetch() throw (int)
{
  EXEC SQL FETCH :emp_cursor INTO :ename, :empno;
  if (sqlca.sqlcode == 1403)
    throw sqlca.sqlcode;     // Like a WHENEVER NOT FOUND statement.
}

void emp::emp_error()
{
  printf("%.*s\n", sqlca.sqlerrm.sqlerrml, sqlca.sqlerrm.sqlerrmc);
  EXEC SQL WHENEVER SQLERROR CONTINUE;
  EXEC SQL ROLLBACK WORK RELEASE;
  exit(1);
}

The main program, cppdemo2.pc, uses the cursor variable:

// Pro*C/C++ sample program demonstrating a simple use of Cursor Variables
// implemented within a C++ class framework.  Build this program as follows
//
//   1. Execute the cppdemo2.sql script within SQL*Plus
//   2. Precompile the empclass.pc program as follows
//      > proc code=cpp sqlcheck=full user=scott/tiger lines=yes empclass
//   3. Precompile the cppdemo2.pc program as follows
//      > proc code=cpp lines=yes cppdemo2
//   4. Compile and Link
//
// Note that you may have to specify various include directories using the
// include option when precompiling.

#include <stdio.h>
#include <stdlib.h>
#include <sqlca.h>

static void sql_error()
{
  printf("%.*s\n", sqlca.sqlerrm.sqlerrml, sqlca.sqlerrm.sqlerrmc);
  EXEC SQL WHENEVER SQLERROR CONTINUE;
  EXEC SQL ROLLBACK WORK RELEASE;
  exit(1);  
}

// Physically include the emp class definition in this module.
EXEC SQL INCLUDE empclass.h;

int main()
{
  EXEC SQL BEGIN DECLARE SECTION;
    char *uid = "scott/tiger";
  EXEC SQL END DECLARE SECTION;

  EXEC SQL WHENEVER SQLERROR DO sql_error();
  EXEC SQL CONNECT :uid;

  emp *e = new emp(); // Invoke Constructor - ALLOCATE Cursor Variable.

  e->open();          // Open the Cursor.

  while (1)
    {
      // Fetch from the Cursor, catching the NOT FOUND condition
      // thrown by the fetch() member function.
      try { e->fetch(); } catch (int code)  
        { if (code == 1403) break; }
      printf("Employee:  %s[%d]\n", e->ename, e->empno);
    }

  e->close();         // Close the Cursor.

  delete e;           // Invoke Destructor - FREE Cursor Variable.

  EXEC SQL ROLLBACK WORK RELEASE;
  return (0);
}

cppdemo3.pc

/*
 * cppdemo3.pc : An example of C++ Inheritance
 *
 * This program finds all salesman and prints their names
 * followed by how much they earn in total (ie; including 
 * any commissions).
 */
 
#include <iostream.h>
#include <stdio.h>
#include <sqlca.h>
#include <string.h>

#define NAMELEN 10

class employee {    // Base class is a simple employee
public:
  char ename[NAMELEN];
  int sal;
  employee(char *, int);
};

employee::employee(char *ename, int sal)
{
  strcpy(this->ename, ename);
  this->sal = sal;
}

// A salesman is a kind of employee
class salesman : public employee
{
  int comm;
public:
  salesman(char *, int, int);
  friend ostream& operator<<(ostream&, salesman&);
};

// Inherits employee attributes
salesman::salesman(char *ename, int sal, int comm)
  : employee(ename, sal), comm(comm) {}  

ostream& operator<<(ostream& s, salesman& m)
{
  return s << m.ename << m.sal + m.comm << endl;  
}

void print(char *ename, int sal, int comm)
{
  salesman man(ename, sal, comm);
  cout << man;
}

main()
{
  EXEC SQL BEGIN DECLARE SECTION;
    char *uid = "scott/tiger";
    char  ename[NAMELEN];
    int   sal, comm;
    short comm_ind;
  EXEC SQL END DECLARE SECTION;

  EXEC SQL WHENEVER SQLERROR GOTO error;

  EXEC SQL CONNECT :uid;
  EXEC SQL DECLARE c CURSOR FOR
    SELECT ename, sal, comm FROM emp WHERE job = 'SALESMAN'
      ORDER BY ename;
  EXEC SQL OPEN c;

  cout << "Name    Salary" << endl << "------  ------" << endl;

  EXEC SQL WHENEVER NOT FOUND DO break;
  while(1)
   {
     EXEC SQL FETCH c INTO :ename, :sal, :comm:comm_ind;
     print(ename, sal, (comm_ind < 0) ? 0 : comm);
   }
  EXEC SQL CLOSE c;
  exit(0);

error:
  cout << endl << sqlca.sqlerrm.sqlerrmc << endl;
  exit(1);
}