# 使用库函数
- ECPGdebug(int on, FILE \*stream)：若函数第一个参数为非0，则开启调试日志，第二个参数表示要打印日志的标准输出流。调试日志在标准输出流上执行，日志包含所有输入的SQL语句以及来自GaussDB Kernel服务器的结果。
  示例：
  ```
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include "sqlca.h"
  int main()
  {
      ECPGdebug(1, stderr);
      EXEC SQL CONNECT postgres;
      EXEC SQL SET AUTOCOMMIT TO ON;
      EXEC SQL CREATE TABLE T1(a int);
      return (0);
  }
  ```
  
- ECPGget_PGconn(const char \*connection_name)：返回由给定名称标识的数据库连接句柄。如果connection_name设置为NULL，则返回当前连接句柄。如果没有连接句柄可以被识别，则该函数返回NULL。
  示例：
  ```
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include "sqlca.h"
  int main()
  {
      ECPGdebug(1, stderr);
      EXEC SQL CONNECT TO postgres as con1;
      EXEC SQL SET AUTOCOMMIT TO ON;
      EXEC SQL DROP TABLE IF EXISTS T1;
      PGconn     *conn;
      conn = ECPGget_PGconn("con1");
      printf("conn = %p\n", conn);
      conn = ECPGget_PGconn(NULL);
      printf("conn = %p\n", conn);
      EXEC SQL CREATE TABLE T1(a int);
      return (0);
  }
  ```
  
- ECPGtransactionStatus(const char \*connection_name)：返回connection_name连接的当前事务状态。可能的返回值包括：
  ```
  PQTRANS_IDLE,    /* connection idle，连接空闲 */
      PQTRANS_ACTIVE,  /* command in progress，命令正在执行 */
      PQTRANS_INTRANS, /* idle, within transaction block，空闲，在事务块里 */
      PQTRANS_INERROR, /* idle, within failed transaction，空闲，在失败的事务里 */
      PQTRANS_UNKNOWN  /* cannot determine status，未知状态 */
  ```
  示例：
  ```
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include "sqlca.h"
  int main()
  {
      ECPGdebug(1, stderr);
      EXEC SQL CONNECT TO postgres as con1;
      EXEC SQL DROP TABLE IF EXISTS T1;
      int a = ECPGtransactionStatus("con1");
      printf("%d\n", a);
      EXEC SQL CREATE TABLE T1(a int);
      EXEC SQL COMMIT;
      return (0);
  }
  ```
  
- ECPGfree_auto_mem()：释放为输出型宿主变量申请的所有内存，在程序结束时调用（return\\exit）。
  示例：
  ```
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include "sqlca.h"
  int main()
  {
     EXEC SQL BEGIN DECLARE SECTION;
     int *ip1=0;
     char **cp2=0;
     int *ipointer1=0;
     int *ipointer2=0;
     int colnum;
     EXEC SQL END DECLARE SECTION;
     int i;
     ECPGdebug(1, stderr);
     EXEC SQL WHENEVER SQLERROR DO sqlprint();
     EXEC SQL CONNECT TO REGRESSDB1;
     EXEC SQL SET DATESTYLE TO postgres;
     EXEC SQL CREATE TABLE test (a int, b text);
     EXEC SQL INSERT INTO test VALUES (1, 'one');
     EXEC SQL INSERT INTO test VALUES (2, 'two');
     EXEC SQL INSERT INTO test VALUES (NULL, 'three');
     EXEC SQL INSERT INTO test VALUES (NULL, NULL);
     EXEC SQL ALLOCATE DESCRIPTOR mydesc;
     EXEC SQL SELECT * INTO SQL DESCRIPTOR mydesc FROM test;
     EXEC SQL GET DESCRIPTOR mydesc :colnum=COUNT;
     EXEC SQL GET DESCRIPPTOR mydesc VALUE 1 :ip1=DATA, :ipointer1=INDICATOR;
     EXEC SQL GET DESCRIPTOR mydesc VALUE 2 :cp2=DATA, :ipointer2=INDICATOR;
     printf("Result (%d columns):\n", colnum);
     for (i=0;i < sqlca.sqlerrd[2];++i)
     {
        if (ipointer1[i]) printf("NULL, ");
        else printf("%d, ",ip1[i]);
        if (ipointer2[i]) printf("NULL, ");
        else printf("'%s', ",cp2[i]);
        printf("\n");
     }
     ECPGfree_auto_mem();
     printf("\n");
     EXEC SQL DEALLOCATE DESCRIPTOR mydesc;
     EXEC SQL ROLLBACK;
     EXEC SQL DISCONNECT;
     return 0;
  }
  ```