C语言 复制指针中的数据
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Copying data in pointers
提问by system
How does one copy the data that is pointed to by another pointer?
如何复制另一个指针指向的数据？
I have the following
我有以下
void *startgpswatchdog(void *ptr)
{
GPSLocation *destination;
*destination = (GPSLocation *) ptr;
Will this do this correctly?
这会正确地做到这一点吗？
I free the data that is passed into thread after passing it, so I need to copy the data.
我把传入线程后的数据释放了，所以我需要复制数据。
回答by Mihran Hovsepyan
If you want to copy data you should allocate new memory via malloc, then copy your memory via memcpy.
如果你想复制数据，你应该通过 分配新的内存malloc，然后通过复制你的内存memcpy。
void *startgpswatchdog(void *ptr)
{
GPSLocation *destination = malloc(sizeof(GPSLocation));
memcpy(destination, ptr, sizeof(GPSLocation));
}
回答by system
You can do it if the pointer you ae copying to actually points at something:
如果您复制到的指针实际上指向某个东西，您可以这样做：
void *startgpswatchdog(void *ptr)
{
GPSLocation *destination = malloc( sizeof( GPSLocation ) );
*destination = * (GPSLocation *) ptr;
}
or perhaps better:
或者更好：
void *startgpswatchdog(void *ptr)
{
GPSLocation destination;
destination = * (GPSLocation *) ptr;
}
回答by yossi
you need to allocate memory before you assign to the address pointed by the pointer. why do you need a pointer here ? why not use
您需要在分配给指针指向的地址之前分配内存。为什么这里需要一个指针？为什么不使用
void *startgpswatchdog(void *ptr)
{
GPSLocation destination;
destination = (GPSLocation) *ptr;
}
and later if you need this variable address just use
稍后如果您需要此变量地址，请使用
&destination
just dont forget its a local variable :)
只是不要忘记它是一个局部变量:)
