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Do you know the difference between "NULL" and "\0"?

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J-Naish
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As the title says, do you know the difference between NULL and "\0?
The both indeed stand for "null", but there is a significant difference. Today I will explain the difference.

About NULL

As you know, the NULL in C/C++ means that pointer does not point to a valid memory address. To be detailed, the NULL in C/C++ is a macro defined in many standard libraries such as <stdio.h> and <stddef.h>. It represents a null pointer constant, which is a special value used to indicate that a pointer does not point to a valid memory address.

The specific definition of NULL can vary depending on the compiler and the C standard. However, it is commonly defined as either ((void *)0) or 0. In either case, NULL is a pointer value that points to the memory address 0.

NULL is used like this:

#include <stddef.h>
int main() {
    int *ptr1 = NULL;
    char *ptr2 = NULL;
    // some code
    // ...
}

As the code above shows, NULL can be used for any kind of pointer variable. NULL is typically defined as ((void *)0), as I mentioned above, which is a void pointer variable. In C/C++, void pointer variables can be converted to other pointer types both implicitly and explicitly. Therefore, if the code above is modified for explicit casting, it can be like:

#include <stddef.h>
int main() {
    // explicit casting of NULL
    // this syntax is not common in this case
    int *ptr1 = (int *)NULL;
    char *ptr2 = (char *)NULL;
    // some code
    // ...
}

In conclusion, NULL is a special macro used with pointer types to represent a null pointer constant; it is not used with non-pointer types.

About \0

On the other hand, \0 is NOT a pointer, rather it is actually a special value in the type char. In the type char of C/C++, every string (array of characters) is terminated with \0, which indicates the end of the string. Therefore, \0 is indeed called "null", but it is different from NULL. While NULL is a macro that represents a null pointer constant, \0 is a character value known as the "null character" or "null terminator".

The difference

See the example below:

#include <stddef.h>
int main() {
    char *str1 = "\0";
    char *str2 = NULL;
    // some code
    // ...
}

In this case, str1 is defined as "\0", which means str1 is an empty string. The pointer str1 points to the memory address where this empty string is stored.

On the other hand, str2 is defined as NULL, which means str2 is a pointer variable that is stored in memory somewhere and its value is a special one called the "null pointer constant". The "null pointer constant" is symbolic value that indicates the absence of a valid pointer target. It does not represent a valid memory address that can be dereferenced or accessed like a regular variable.

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