删除动态对象的错误

Question

我正在为堆分配一个内存的内存，当联合的元素Id为900时，我需要删除联合对象。

当Id为900时，请帮助我删除groupUnion[i]对象以下是我的代码。

groupUnion = (SettingsUnion *) malloc(sizeof(SettingsUnion) * (NumAttrs + 1));
if(groupUnion == (SettingsUnion *) NULL)
{
    return (FALSE);
}
for (unsigned int i=0; i < NumAttrs; i++)
{
    inFile.read(reinterpret_cast<char*>(&groupUnion[i]),sizeof(SettingsUnion));
    if(groupUnion[i].Id == 900)
    {
        free groupUnion[i]; // this is bad how can i delete groupUnion[i] when groupUnion[i].Id == 900
        groupUnion[i] = NULL;
    }
}
inFile.close()

预先感谢！

Answer 1

您的代码片段 free groupUnion[i];groupUnion[i] = NULL让我假设您实际上想向SettingUnion -Objects 表示 pointer的数组，而不是SettingUnion -Objects的数组。因此，您的代码看起来如下(我使用了您的malloc/free-风格，尽管在C 中，您实际上会使用new/delete(：

groupUnion = (SettingsUnion **) malloc(sizeof(SettingsUnion*) * (NumAttrs + 1));
if(groupUnion == NULL)
{
    return (FALSE);
}
for (unsigned int i=0; i < NumAttrs; i++)
{
    groupUnion[i] = malloc(sizeof(SettingsUnion));
    inFile.read(reinterpret_cast<char*>(&groupUnion[i]),sizeof(SettingsUnion));
    if(groupUnion[i]->Id == 900)
    {
        free groupUnion[i];
        groupUnion[i] = NULL;
    }
}
inFile.close()

Answer 2

您无法释放分配的内存的一部分：Free groupunion [i]

但是，您可以做的是单独分配元素，然后单独释放它们：

// not sure why you need the +1 (anyway you allocate an array of pointers to the struct here. Consider using new operator)
groupUnion = (SettingsUnion **) malloc(sizeof(SettingsUnion *) * (NumAttrs + 1)); 
if(groupUnion == (SettingsUnion *) NULL)
{
    return (FALSE);
}
for (unsigned int i=0; i < NumAttrs; i++)
{
    // you allocate the individual groupUnion here:
    groupUnion[i] = (SettingsUnion *) malloc(sizeof(SettingsUnion));
    if(groupUnion[i] == (SettingsUnion *) NULL)
    {
        return (FALSE);
    }
    inFile.read(reinterpret_cast<char*>(&groupUnion[i]),sizeof(SettingsUnion));
   if(groupUnion[i].Id == 900)
   {
        free groupUnion[i]; // this is bad how can i delete groupUnion[i] when groupUnion[i].Id == 900
        groupUnion[i] = NULL;
   }
}
inFile.close()