Error use of undeclared identifier null c

This didn' t happen in VS. When I go to my code and ' hover' over " NULL", a window is shown " # define NULL 0". I can right- click on NULL and. Three options: include the header < cstddef> which defines NULL; use a null pointer constant, 0 or ( since C+ + 11) nullptr rather than a dodgy macro; don' t compare with null, just use the pointer itself in a boolean context for the. cpp: 6: 9: error: use of undeclared identifier ' NULL' : throw( NULL) ;. On the other hand c+ + 11 onwards, nullptr is a keyword and doesn' t require a header. How to use throw. Avoid throwing NULL or nullptr and prefer throwing object of class that is derived from std: : exception. If you really really really like to type nullptr in C, you can use. Notice that C has the NULL macro from < stddef. h> ; it is readable too, but its expansion is implementation- defined, so it might be either ( ( void* ) 0) or 0 ( fining your own NULL value is not standard, and very error prone and that will for sure give you no sleep nights.

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  • Video:Error identifier null

    Error identifier undeclared

    gnueabi/ sysroot/ usr/ include/ linux/ i2c- dev. h: 175: error: ' NULL' undeclared ( first use in this function) / / / return. However you can use 0 or nullptr too. NULL isn' t actually part of the core C or C+ + language; it' s defined to be 0 in stddef. Since you' re using C + +, prefer nullptr, which is a keyword, and typed. ( Assuming it' s. linkedlist\ linkedlist. h| | In constructor ` Node: : Node( int) ' : | \ linkedlist\ linkedlist. h| 9| error: ` NULL' was not declared in this scope| | | = = = Build finished: 1 errors,. In newer C+ + ( C+ + 11 and higher), use nullptr ( as pointed out in a comment, thanks).

    NULL is not a built- in constant in the C or C+ + languages. In fact, in C+ + it' s more or less obsolete, just use a plain literal 0 instead, the compiler will do the right thing depending on the context. In newer C+ + ( C+ + 11 ' s an identifier defined in some standard headers. The preferred way in C+ + 11 is to use the new nullptr keyword, which is implemented in GCC since version 4. nullptr is not implicitly convertible to integral types, so it cluding a header multiple times is no problem ( if the header is not horribly broken, which the standard headers. NULL is only a define with a value of 0. But if you have access to C+ + 11, I would recommend using nullptr.