可能的空指针取消引用-否则将其检查为空是多余的 [英] Possible null pointer dereference - otherwise it is redundant to check it against null

问题描述

我有以下代码，这些代码正常工作：

I have the following code, which is working properly:

int result = ERRORCODE_OK;
if (dataObj == NULL || dataObj->inputSignal == NULL)
{
   result = ERRORCODE_MISSING_DATAOBJ;
}
if (result == ERRORCODE_OK && dataObj->spectrum == NULL) // CPP-Check error
{
   result = Calculate(dataObj->inputSignal, .. );
} 
return result;

但是CppCheck给我以下错误：

But CppCheck gives me the following error:

可能的空指针取消引用： dataObj -否则将其检查为空是多余的。

Possible null pointer dereference: dataObj - otherwise it is redundant to check it against null.

我不明白为什么。如果 dataobj 为 NULL ，则结果将为 ERRORCODE_OK 。

I don't understand why. If the dataobj is NULL, then the result will be something else then ERRORCODE_OK.

推荐答案

CppCheck进行的检查不够深入，以至于您的第二个条件不能得到充分评估第一个成功：

CppCheck doesn't inspect deep enough to see that your second condition won't be fully evaluated if the first one succeeds:

int result = ERRORCODE_OK;
if (dataObj == NULL || dataObj->inputSignal == NULL)
    result = ERRORCODE_MISSING_DATAOBJ;

// Here, you can see that either dataObj!=NULL or result!=ERRORCODE_OK.
// But CppCheck can't!

if (result == ERRORCODE_OK && dataObj->spectrum == NULL)
    result = Calculate(dataObj->inputSignal, .. );
return result;

安抚检查器的三种替代方法显示出来。首先，只需在第二个 if 中重复检查 dataObj 是否为空。其次，将第二个 if 更改为 else if ：

Three alternative ways of pacifying the checker present themselves. Firstly, just repeat the check that dataObj is non-null in the second if. Secondly, change the second if to else if:

int result = ERRORCODE_OK;
if (dataObj == NULL || dataObj->inputSignal == NULL)
{
    result = ERRORCODE_MISSING_DATAOBJ;
}
else if (result == ERRORCODE_OK && dataObj->spectrum == NULL)
{
    result = Calculate(dataObj->inputSignal, .. );
} 
return result;

第三，一旦发现以下错误情况之一，请立即返回：

Thirdly, return as soon as you find one of the error cases:

if (!dataObj || !dataObj->inputSignal)
    return ERRORCODE_MISSING_DATAOBJ;
if (dataObj->spectrum)
    return ERRORCODE_OK;
return Calculate(dataObj->inputSignal, .. );

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