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<TITLE>Fetching Data</TITLE>
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<TD colspan="3" class="big">Fetching data from a result set</TD>
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<TR>
<TD colspan="3"><P>If the execution of the statement went fine you are now able to fetch
the data <A Href="gloss.html#col">column</A> by column. May be you would first like to know
how many columns there are in the result set (if you use a <CODE> SELECT * FROM tkeyuser</CODE>
you wouldn't know in your program). A call to <a href="gloss.html#ccol"><CODE>SQLNumResultCols</CODE></A>.
This function takes the statement handle and a pointer to an integer variable which will yield the
number of columns after the call.</P>
Knowing that much we can add this to our program:
<CODE><PRE>
<FONT COLOR="green">// At the beginning add:</FONT>
SQLSMALLINT V_OD_colanz; <FONT COLOR="green">// Num of columns</FONT>
<FONT COLOR="green">// At the end add:</FONT>
V_OD_erg=SQLNumResultCols(V_OD_hstmt,&V_OD_colanz);
if ((V_OD_erg != SQL_SUCCESS) &&
(V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Fehler im ResultCols %d\n",V_OD_erg);
SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
printf("Number of Columns %d\n",V_OD_colanz);
</PRE></CODE>
<P>
The next thing you need to know is how many <A href="gloss.html#row">rows</A> have
been returned by the query. A call to <A HREF="gloss.html#crow"><CODE>SQLRowCount</CODE></A> should
quench your thirst for knowledge.
</P>
<P>
The last thing to do is to fetch the data itself from the result set. You should call <A HREF="gloss.html#fetc"><CODE>SQLFetch</CODE></A>
with a statement handle (which has been allocated and <CODE>SQLBind</CODE> has been called for all columns).
<CODE>SQLFetch</CODE> returns <CODE>SQL_NO_DATA</CODE> if there is no more data in the result set.
</P>
<P>So here is the complete source code. Real C-programmers will moan in disgust
how inefficient the program is coded, but I prefer it that way (doesn't it look a little bit like PASCAL?).
Take it as a starting point for your own endeavors with ODBC.</P>
<CODE class="list"><PRE>
/* odbc.c
testing unixODBC
*/
#include <stdlib.h>
#include <stdio.h>
#include <odbc/sql.h>
#include <odbc/sqlext.h>
#include <odbc/sqltypes.h>
SQLHENV V_OD_Env; <FONT COLOR="green">// Handle ODBC environment</FONT>
long V_OD_erg; <FONT COLOR="green">// result of functions</FONT>
SQLHDBC V_OD_hdbc; <FONT COLOR="green">// Handle connection</FONT>
char V_OD_stat[10]; <FONT COLOR="green">// Status SQL</FONT>
SQLINTEGER V_OD_err,V_OD_rowanz,V_OD_id;
SQLSMALLINT V_OD_mlen,V_OD_colanz;
char V_OD_msg[200],V_OD_buffer[200];
int main(int argc,char *argv[])
{
<FONT COLOR="green">// 1. allocate Environment handle and register version </FONT>
V_OD_erg=SQLAllocHandle(SQL_HANDLE_ENV,SQL_NULL_HANDLE,&V_OD_Env);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Error AllocHandle\n");
exit(0);
}
V_OD_erg=SQLSetEnvAttr(V_OD_Env, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Error SetEnv\n");
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
<FONT COLOR="green">// 2. allocate connection handle, set timeout</FONT>
V_OD_erg = SQLAllocHandle(SQL_HANDLE_DBC, V_OD_Env, &V_OD_hdbc);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Error AllocHDB %d\n",V_OD_erg);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
SQLSetConnectAttr(V_OD_hdbc, SQL_LOGIN_TIMEOUT, (SQLPOINTER *)5, 0);
<FONT COLOR="green">// 3. Connect to the datasource "web" </FONT>
V_OD_erg = SQLConnect(V_OD_hdbc, (SQLCHAR*) "web", SQL_NTS,
(SQLCHAR*) "christa", SQL_NTS,
(SQLCHAR*) "", SQL_NTS);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Error SQLConnect %d\n",V_OD_erg);
SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1,
V_OD_stat, &V_OD_err,V_OD_msg,100,&V_OD_mlen);
printf("%s (%d)\n",V_OD_msg,V_OD_err);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
printf("Connected !\n");
V_OD_erg=SQLAllocHandle(SQL_HANDLE_STMT, V_OD_hdbc, &V_OD_hstmt);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Fehler im AllocStatement %d\n",V_OD_erg);
SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1, V_OD_stat,&V_OD_err,V_OD_msg,100,&V_OD_mlen);
printf("%s (%d)\n",V_OD_msg,V_OD_err);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
SQLBindCol(V_OD_hstmt,1,SQL_C_CHAR, &V_OD_buffer,150,&V_OD_err);
SQLBindCol(V_OD_hstmt,2,SQL_C_ULONG,&V_OD_id,150,&V_OD_err);
V_OD_erg=SQLExecDirect(V_OD_hstmt,"SELECT dtname,iduser FROM tkeyuser order by iduser",SQL_NTS);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Error in Select %d\n",V_OD_erg);
SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1, V_OD_stat,&V_OD_err,V_OD_msg,100,&V_OD_mlen);
printf("%s (%d)\n",V_OD_msg,V_OD_err);
SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
V_OD_erg=SQLNumResultCols(V_OD_hstmt,&V_OD_colanz);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
SQLDisconnect(V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
printf("Number of Columns %d\n",V_OD_colanz);
V_OD_erg=SQLRowCount(V_OD_hstmt,&V_OD_rowanz);
if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
{
printf("Number ofRowCount %d\n",V_OD_erg);
SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
SQLDisconnect(V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
exit(0);
}
printf("Number of Rows %d\n",V_OD_rowanz);
V_OD_erg=SQLFetch(V_OD_hstmt);
while(V_OD_erg != SQL_NO_DATA)
{
printf("Result: %d %s\n",V_OD_id,V_OD_buffer);
V_OD_erg=SQLFetch(V_OD_hstmt);
} ;
SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
SQLDisconnect(V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
return(0);
}
</PRE>
</CODE>
If I find some more time I will add something about diagnostics, cursor positioning updating and and and...
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