一、头文件

引入informix数据库的头文件时，可使用如下的方式：

EXEC SQL INCLUDE sqlca;
EXEC SQL INCLUDE sqlda;
EXEC SQL INCLUDE sqlhdr;
EXEC SQL INCLUDE decimal;
EXEC SQL INCLUDE locator;
EXEC SQL INCLUDE varchar;
EXEC SQL INCLUDE datetime;
EXEC SQL INCLUDE sqlstype;
EXEC SQL INCLUDE sqltypes;
EXEC SQL INCLUDE sqlstype;

二、宏定义

宏在宿主变量使用时，此宏定义可使用如下方式：

EXEC SQL DEFINE SQL_USRNAME_MAX_LEN 64;   /* User name max len */
EXEC SQL DEFINE SQL_PASSWD_MAX_LEN 64;    /* Password max len */
EXEC SQL DEFINE SQL_SVRNAME_MAX_LEN 64;   /* Database name max len */
EXEC SQL DEFINE SQL_CNNAME_MAX_LEN 64;    /* Connect name max len */
EXEC SQL DEFINE SQL_STMT_MAX_LEN 1024;    /* SQL statement max len */

三、结构体定义

当SQL语句中使用了结构体变量时，那么此变量的类型结构体必须通过如下方式定义：

EXEC SQL BEGIN DECLARE SECTION;
typedef struct
{
    int id;
    char name[32];
    char gender;
    int age;
    char brf[256];
}DBStudent_t;
EXEC SQL END DECLARE SECTION;

如：

int db_ifx_update(...)
{
EXEC SQL BEGIN DECLARE SECTION;
    DBStudent_t dbstudent;
EXEC SQL END DECLARE SECTION;

    ...

    EXEC SQL UPDATE SET *=(:dbstudent) WHERE id='10001';
}

四、变量定义
宿主变量的必须通过如下方式进行定义：

EXEC SQL BEGIN DECLARE SECTION;
    char svrname[SQL_SVRNAME_MAX_LEN], /* Server name */
         usrname[SQL_USRNAME_MAX_LEN], /* User name */
         passwd[SQL_PASSWD_MAX_LEN],   /* Passwd */
         cnname[SQL_CNNAME_MAX_LEN];   /* Connect name */
EXEC SQL END DECLARE SECTION;

int db_ifx_open(...)
{
EXEC SQL BEGIN DECLARE SECTION;
    char svrname[SQL_SVRNAME_MAX_LEN], /* Server name */
         usrname[SQL_USRNAME_MAX_LEN], /* User name */
         passwd[SQL_PASSWD_MAX_LEN],   /* Passwd */
         cnname[SQL_CNNAME_MAX_LEN];   /* Connect name */
EXEC SQL END DECLARE SECTION;

    ...

    EXEC SQL CONNECT TO :svrname AS :cnname USER :usrname USING :passwd;
    ...
}

五、错误信息
每执行一次SQL语句后，错误码存放在全局变量sqlca.sqlcode中，可通过rgetmsg()获取错误信息。如：

int db_ifx_commit(...)
{
    EXEC SQL COMMIT WORK;
    if(sqlca.sqlcode < 0)
    {
        rgetmsg(sqlca.sqlcode, errmsg, sizeof(errmsg));
        fprintf(stdout, "%s", errmsg);
        return -1;
    }
    ...
}