问一个or执行顺序的问题(30分)

S

siaosa

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• 2008-08-23

• #1

为什么这个判断语句经常会出错?应该怎么改才好?<br>if (ADODataSet1.FieldValues['field1'] =NULL) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;//这个地方正常<br>&nbsp;or (ADODataSet1.FieldValues['field1'].AsString='') then &nbsp; //这个地方会出错,系统报异常

 

B

bahamut8348

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• 2008-08-23

• #2

改成FieldByName().AsString好了

 

Z

zkktom

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• 2008-08-23

• #3

这个问题其实很简单<br>写成两条才可以<br>if (ADODataSet1.FieldValues['field1'] =NULL) &nbsp; &nbsp; then &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //这个地方正常<br>&nbsp;if &nbsp;(ADODataSet1.FieldValues['field1'].AsString='') then &nbsp; //这个地方会出错,系统<br><br>列：fm:Tform;<br>&nbsp; &nbsp; if (fm)=nil or (fm.name='XXX') &nbsp;then<br>&nbsp; &nbsp;如果你不初始化，肯定报错！

 

S

siaosa

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• 2008-08-23

• #4

OR运算时,不是只要第一个条件为真,系统就不再判断第二个条件吗?

 

无

无欲则刚

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• 2008-08-23

• #5

你说的很对 第一条为真就不判断第二条了

 

S

siaosa

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• 2008-08-23

• #6

这个问题就是系统当第一个条件为真时，还去判断第二个条件了。

 

S

szhcracker

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• 2008-08-24

• #7

if (ADODataSet1.FieldValues['field1'] =NULL) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;//这个地方正常<br>&nbsp;or (ADODataSet1.FieldValues['field1'].AsString='') then ...<br><br>改为<br>if (ADODataSet1.FieldValues['field1'].IsNull) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;//这个地方正常<br>&nbsp;or (ADODataSet1.FieldValues['field1'].AsString='') then ...<br>不知道可行否？

 

S

siaosa

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• 2008-08-24

• #8

(ADODataSet1.FieldValues['field1'].AsString='') then &nbsp; 这一句改成<br>&nbsp;(VarAsType(ADODataSet1.FieldValues['field1'],varString) &nbsp;then &nbsp; 问题解决