MasteringVFP/4/7/2

http://www.textcachivirovir.com 
==== seek ====
èªå¾ä¸ç¥ç¬¬å¹¾çç VFP æä¾ Seek() éåå½æ¸, å°±æ²åç¨ Seek çå½ä»¤, ä¸éååç VFP8 ç Help æç¼ç¾åä¾ Seek å½ä»¤ä¹å¤äºä¸å°åæ¸å¯ä»¥ä¸, éæ¯ä»¥åé½æ²æ³¨æå¢?
<pre>
SEEK eExpression   [ORDER nIndexNumber | IDXIndexFileName
    | [TAG] TagName [OF CDXFileName]    [ASCENDING | DESCENDING]]
   [IN nWorkArea | cTableAlias]
</pre>
Seek ä¸è«å½æ¸æå½ä»¤é½å¿é äºåå»ºç« Index, ç¨éçè§£éå¤§æ¦å°±æ¯:è³æåº«å»ºç«éç´¢å¼å¾, ä½¿ç¨è©²æä»¤æ¾å°å°ç¬¦åæ¢ä»¶çç¬¬ä¸çè¨é, å¦ææ¾ä¸å°å°ç§»åå°æå¾, å¯ç¨ Found() æ Eof() ä¾å¤æ·ã
ä½¿ç¨ Seek(), å¦æ Set("Near")="OFF" çè©±, ä¸ç¬¦åæ¢ä»¶, è¨éå°ç§»åå°æå¾, å¦æ Set("Near")="ON", ä¸ç¬¦åæ¢ä»¶, è¨éå°ç§»åå°æç¬¦åæ¢ä»¶çè¨éç·¨èãSeek çå½ä»¤åç¡æ³åå°åè¿°åè½ã

æåå°±ä¾ççä»¥ä¸çå¹¾åä¾å~
----
(1)
<pre>
Set Near on
CREATE CURSOR ABC(Field1 C(5))
INDEX ON field1 TO XYZ
INSERT INTO ABC (Field1) Value("1")
INSERT INTO ABC (Field1) Value("2")
INSERT INTO ABC (Field1) Value("4")
INSERT INTO ABC (Field1) Value("5")
SEEK "3"
? Eof()
</pre>
ä¸è¿° Eof() å°åå³ .T., è¡¨ç¤ºæ¾ä¸å° "3", è¨éä¹ç§»åå°æå¾
ä¸éå¦æä½¿ç¨ä»¥ä¸å½ä»¤
<pre>
?Seek("3")
?Recno()
</pre>
å°åå³ .F., è¨éå»æåçå¨ç¬¬ 3 ç, ä¹å°±æ¯ Field1="4" çä½ç½®, èä¸æç§»åå°æå¾
æ¨å¯ä»¥è©¦è©¦ç Set Near Off åæç¼çä»éº¼ææ³
----
(2)
<pre>
Set Exact off
CREATE CURSOR ABC(Field1 C(5))
INDEX ON field1 TO XYZ
INSERT INTO ABC (Field1) Value("11")
INSERT INTO ABC (Field1) Value("22")
?SEEK("2")
</pre>
ä¸è¿°è¨å® Exact çº Off, æ¢ä»¶æ¥è©¢æå çºæ¥å°ç¬¬äºç 22 çç¬¬ä¸å 2, æä»¥æ¯è¢«äºè¨±ç¬¦åæ¢ä»¶
ä½æ¯ç¶ Exact è¨å®çº On æ, é£è¦ç¬¦åæ¢ä»¶, åªè½ä¸ Seek("22") æç®ç¬¦åæ¢ä»¶ã