Where / How is null defined?

Question

Null is not declared?

My code:

// Include necessary libraries #include <cstdlib> // Exits #include <iostream> // I/O #include <cstring> // String functions using namespace std; int main(int argc, char *argv[]) { //Declare local Constants and Variables const char SOKINP[19] = "23456789TtJjQqKkAa"; // Valid Input Characters char acCards [5]; // Array to hold up to five cards (user input) bool bErr; // Loop on Error (Calculated) int i, // Loop variable (Calculated) iNbrCrd, // Number of Cards 2-5 (user input) iNAces, // Number of Aces (Calculated) iTS; // Total Score (Calculated) ... for (i=0;i<iNbrCrd;i++){ do { cout << "Enter Card #" << i << " (2-9,t,j,q,k or a) >"; cin >> acCards[i]; cout << endl; bErr = (strchr(SOKINP, acCards[i]) == null) ? true : false; // *ERROR* } while (bErr); } return EXIT_SUCCESS; }

[Error] 'null' was not declared in this scope

How do I declare 'null'? I tried including several other libraries. I'm using Dev C++ v5.4.2

Thanks, ~d

@ta.speot.is: You should say : Use nullptr (or NULL). The order emphasizes and the emphasise matters. — Sarfaraz Nawaz
– Sarfaraz Nawaz, Commented Sep 29, 2013 at 4:46
@ta.speot.is In this case, you should say: "don't use Dev-C++ but a good C++ compiler, and use nullptr". — user529758
– user529758, Commented Sep 29, 2013 at 4:51
@CareyGregory: this topic gives lots of such example. See every answer. — Sarfaraz Nawaz
– Sarfaraz Nawaz, Commented Sep 29, 2013 at 5:03

Yu Hao · Accepted Answer · 2013-09-29 04:52:22Z

6

Its not null. It's NULL in all caps. If writing NULL does not work, you can define it yourself by using

#define NULL 0

edited Sep 29, 2013 at 4:52

Yu Hao

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answered Sep 29, 2013 at 4:47

The Light Spark

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2 Comments

user529758 Over a year ago

@ValekHalfHeart You will get type mismatch warnings exactly when you define it as (void *)0. In C and C++, 0 is a valid literal for null pointers of any type, but (void *)0 only works with pointers to void, due to strict strong typing in C++. Thus, (void *)0 is safer in C than 0, but it's wrong in C++.

Dave C Over a year ago

Noob mistake. Doh! Thank you everyone, capitalizing it was the answer.

Saksham · Accepted Answer · 2013-09-29 04:58:55Z

Use NULL instead of Null.

If you are using it to initialize a pointer and you are using C++11, use nullptr.

Although NULL works for assigning the pointers(even though NULL is not a pointer type but is integer), you may face problems in the below case:

void func(int n); void func(char *s); func( NULL ); // guess which function gets called?

Refer to THIS for more details

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