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One of job interview questions on C pointers here is the following: what is null pointer assignment error?
I've googled for a while and don't see any reasonable explanation. What is that? Trying to write through a null pointer? Something architecture- or environment-specific? What exactly is that error?
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A null pointer is a pointer which points nothing. Some uses of the null pointer are: a) To initialize a pointer variable when that pointer variable isn't assigned any valid memory address yet. b) To pass a null pointer to a function argument when we don't want to pass any valid memory address.
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Extended Description. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions.
What you need to know is that you cannot undo an assignment, so whatever value the pointer contains will be lost. This is the only direct consequence of reassigning a pointer, null or not null. Any problems will be a consequence of no longer having access the previous value.
A null pointer has a reserved value that is called a null pointer constant for indicating that the pointer does not point to any valid object or function. You can use null pointers in the following cases: Initialize pointers. Represent conditions such as the end of a list of unknown length.
There are many scenarios where you can see problems. But the key thing is, you did not allocate the memory correctly. The following code would produce Null pointer assignment error message after you run the program. Note: It will compile correctly.
void CopyMessage(char *p)
{
strcpy(p, "welcome");
}
void main()
{
char *src;
CopyMessage(src);
}
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