Sql server 为什么SqlSetsTMStattr将StringLength设置为0
在这个例子中Sql server 为什么SqlSetsTMStattr将StringLength设置为0,sql-server,database,odbc,Sql Server,Database,Odbc,在这个例子中 #define ROW_ARRAY_SIZE 10 // Define the ORDERINFO struct and allocate an array of 10 structs. typedef struct { SQLUINTEGER OrderID; SQLINTEGER OrderIDInd; SQLCHAR SalesPerson[11]; SQLINTEGER SalesPersonLe
#define ROW_ARRAY_SIZE 10
// Define the ORDERINFO struct and allocate an array of 10 structs.
typedef struct {
SQLUINTEGER OrderID;
SQLINTEGER OrderIDInd;
SQLCHAR SalesPerson[11];
SQLINTEGER SalesPersonLenOrInd;
SQLCHAR Status[7];
SQLINTEGER StatusLenOrInd;
} ORDERINFO;
ORDERINFO OrderInfoArray[ROW_ARRAY_SIZE];
SQLULEN NumRowsFetched;
SQLUSMALLINT RowStatusArray[ROW_ARRAY_SIZE], i;
SQLRETURN rc;
SQLHSTMT hstmt;
// Specify the size of the structure with the SQL_ATTR_ROW_BIND_TYPE
// statement attribute. This also declares that row-wise binding will
// be used. Declare the rowset size with the SQL_ATTR_ROW_ARRAY_SIZE
// statement attribute. Set the SQL_ATTR_ROW_STATUS_PTR statement
// attribute to point to the row status array. Set the
// SQL_ATTR_ROWS_FETCHED_PTR statement attribute to point to
// NumRowsFetched.
SQLSetStmtAttr(hstmt, SQL_ATTR_ROW_BIND_TYPE, sizeof(ORDERINFO), 0);
SQLSetStmtAttr(hstmt, SQL_ATTR_ROW_ARRAY_SIZE, ROW_ARRAY_SIZE, 0);
SQLSetStmtAttr(hstmt, SQL_ATTR_ROW_STATUS_PTR, RowStatusArray, 0);
SQLSetStmtAttr(hstmt, SQL_ATTR_ROWS_FETCHED_PTR, &NumRowsFetched, 0);
// Bind elements of the first structure in the array to the OrderID,
// SalesPerson, and Status columns.
SQLBindCol(hstmt, 1, SQL_C_ULONG, &OrderInfoArray[0].OrderID, 0, &OrderInfoArray[0].OrderIDInd);
SQLBindCol(hstmt, 2, SQL_C_CHAR, OrderInfoArray[0].SalesPerson,
sizeof(OrderInfoArray[0].SalesPerson),
&OrderInfoArray[0].SalesPersonLenOrInd);
SQLBindCol(hstmt, 3, SQL_C_CHAR, OrderInfoArray[0].Status,
sizeof(OrderInfoArray[0].Status), &OrderInfoArray[0].StatusLenOrInd);
// Execute a statement to retrieve rows from the Orders table.
SQLExecDirect(hstmt, "SELECT OrderID, SalesPerson, Status FROM Orders", SQL_NTS);
// Fetch up to the rowset size number of rows at a time. Print the actual
// number of rows fetched; this number is returned in NumRowsFetched.
// Check the row status array to print only those rows successfully
// fetched. Code to check if rc equals SQL_SUCCESS_WITH_INFO or
// SQL_ERRORnot shown.
while ((rc = SQLFetchScroll(hstmt,SQL_FETCH_NEXT,0)) != SQL_NO_DATA) {
for (i = 0; i < NumRowsFetched; i++) {
if (RowStatusArray[i] == SQL_ROW_SUCCESS|| RowStatusArray[i] ==
SQL_ROW_SUCCESS_WITH_INFO) {
if (OrderInfoArray[i].OrderIDInd == SQL_NULL_DATA)
printf(" NULL ");
else
printf("%d\t", OrderInfoArray[i].OrderID);
if (OrderInfoArray[i].SalesPersonLenOrInd == SQL_NULL_DATA)
printf(" NULL ");
else
printf("%s\t", OrderInfoArray[i].SalesPerson);
if (OrderInfoArray[i].StatusLenOrInd == SQL_NULL_DATA)
printf(" NULL\n");
else
printf("%s\n", OrderInfoArray[i].Status);
}
}
}
// Close the cursor.
SQLCloseCursor(hstmt);
然而,根据文件:
如果ValuePtr是指向字符串的指针,则StringLength为
字符串或SQL语句的长度
如果ValuePtr是指向二进制缓冲区的指针,则应用程序
将SQL_LEN_BINARY_ATTR(length)宏的结果放入
弦长。这会在StringLength中放置负值
如果ValuePtr是指向字符串或字符串以外的值的指针
二进制字符串,则StringLength的值应为SQL\u IS\u指针
如果ValuePtr包含固定长度值,则StringLength为
SQL_是整数或SQL_是整数(视情况而定)
除非ValuPtr是零长度数组,否则似乎没有将其设置为0的选项
我错过了什么
SQLSetStmtAttr(hstmt, SQL_ATTR_ROW_BIND_TYPE, sizeof(ORDERINFO), 0);
SQLSetStmtAttr(hstmt, SQL_ATTR_ROW_ARRAY_SIZE, ROW_ARRAY_SIZE, 0);
SQLSetStmtAttr(hstmt, SQL_ATTR_ROW_STATUS_PTR, RowStatusArray, 0);
SQLSetStmtAttr(hstmt, SQL_ATTR_ROWS_FETCHED_PTR, &NumRowsFetched, 0);