Esempio di script C++ per la connessione ODBC

Esempio  di script C++ per la connessione ODBC  compilabile  con Dev-c++  e con Borland C++ builder standard

 In  Visual C++  2005  e successive  potrebbe essere necessario sostituire i SQLCHAR con SQLWCHAR la cui assegnazione  deve essere nel formato  SQLWCHAR szVar[1024] L"Testo assegnato"; per via di UNICODE e il print della variabile    usa l'operatore %ls   invece che %s .

Per la compilazione sono necessarie le librerie odbc32.lib in borland  oppure  libodbc32.a in Dev-c++

In caso di  Linker Error: Unresolved external '_SQLAllocHandle' :

Eseguire il comando nella cartella Bin di borland

implib -a odbc32.lib c:\windows\system32\odbc32.dll

sostituire tutti i vecchi  odbc32.lib dalle cartelle 

Lib/

Lib/Debug/

Lib/Release/

 con il file creato  da implib

Le librerie vanno linkate nel progetto

Project->Add to project 

nella sezione download  è presente il file odbc32.lib già pronto per Borland C++ Builder

 Fonte : http://www.easysoft.com/developer/languages/c/odbc_tutorial.html

 msdn Reference : https://msdn.microsoft.com/en-us/library/ms714177%28v=vs.85%29.aspx

 Reference C++:  http://www.cplusplus.com/reference/

//---------------------------------------------------------------------------
 #include <cstdio>
 #include <windows.h>
 //#include <odbcinst.h>
 #include <sql.h>
 #include <sqlext.h>
 #include <sqltypes.h>
 #pragma hdrstop

 //---------------------------------------------------------------------------

 #pragma argsused


 int main() {
   SQLHENV env;
   SQLHDBC dbc;
   SQLHSTMT stmt;
   SQLRETURN ret; /* ODBC API return status */
   SQLCHAR outstr[1024];
   SQLSMALLINT outstrlen;
   SQLSMALLINT columns; /* number of columns in result-set */
   int row = 0; 
   //int num = 0;
   UCHAR                   szDSN[SQL_MAX_DSN_LENGTH] ="DSN=dbdati;";                // Data Source Name buffer
   UCHAR*                  szUID = NULL;// User ID buffer
   UCHAR*                  szPasswd = NULL;// Password buffer
   UCHAR                   szModel[128];// Model buffer
   SDWORD             cbModel;// Model buffer bytes recieved
   UCHAR                   szSqlStr[] = "select * from tabella1;";    // SQL string
   RETCODE              retcode;// Return code


   /* Allocate an environment handle */
   SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &env);
   /* We want ODBC 3 support */
   SQLSetEnvAttr(env, SQL_ATTR_ODBC_VERSION, (void *) SQL_OV_ODBC3, 0);
   /* Allocate a connection handle */
   SQLAllocHandle(SQL_HANDLE_DBC, env, &dbc);

   // retcode = SQLConnect (hDBC, szDSN, SQL_NTS, szUID,SQL_NTS, szPasswd, SQL_NTS);

   /* Connect to the DSN mydsn */
   ret = SQLDriverConnect(dbc, NULL, szDSN, SQL_NTS,
              outstr, sizeof(outstr), &outstrlen,
              SQL_DRIVER_COMPLETE);
   if (SQL_SUCCEEDED(ret)) {
     printf("Connected\n");
     printf("Returned connection string was:\n\t%s\n", outstr);
       /* Allocate a statement handle */
        SQLAllocHandle(SQL_HANDLE_STMT, dbc, &stmt);
       SQLExecDirect(stmt, szSqlStr, SQL_NTS);
  
  
      //SQLTables(stmt, NULL, 0, NULL, 0, NULL, 0, "tab_utenti", SQL_NTS);
     /* How many columns are there */
     SQLNumResultCols(stmt, &columns);
     printf("Columns %d\n", columns);
     /* debug check for error  */ 
     ret = SQLFetch(stmt);
     printf("Fetch error %d\n", ret);
     /* Loop through the rows in the result-set */
     while (SQL_SUCCEEDED(ret = SQLFetch(stmt))) {
         SQLUSMALLINT i;
         printf("Row %d\n", row++);
         /* Loop through the columns */
         for (i = 1; i <= columns; i++) {
             SQLINTEGER indicator;
             char buf[512];
             /* retrieve column data as a string */
                ret = SQLGetData(stmt, i, SQL_C_CHAR,
                              buf, sizeof(buf), &indicator);
             if (SQL_SUCCEEDED(ret)) {
                 /* Handle null columns */
                 if (indicator == SQL_NULL_DATA) strcpy(buf, "NULL");
                 printf("  Column %u : %s\n", i, buf);
              }
         }
     }
     SQLDisconnect(dbc);        /* disconnect from driver */
     SQLFreeHandle(SQL_HANDLE_ENV, stmt);
   } else {
     fprintf(stderr, "Failed to connect\n");
     //extract_error("SQLDriverConnect", dbc, SQL_HANDLE_DBC);
   }
   
   /* free up allocated handles */

   SQLFreeHandle(SQL_HANDLE_DBC, dbc);
   SQLFreeHandle(SQL_HANDLE_ENV, env);
   
   //scanf("%d",&num);
   getchar();
   return 0;
   
 }