Null and nullptr

Hello everyone , I meet you again , I'm your friend, Quan Jun .

traditionally ,c++ hold NULL、0 As the same thing , Some compilers will NULL Defined as （（void*）0）, Some define it as 0.

c++ It is not allowed to directly transfer void* Implicitly convert to other types , But if NULL Is defined as （（void*）0）,

Compile char *p = NULL;

NULL It has to be defined as 0.

also ：

void func（int）;

void func（char*）;

If NULL Is defined as 0,func（NULL） Going to call void func（int）, This is not reasonable

So the introduction of nullptr, Used specifically to distinguish 0、NULL.

nullptr The type of nullptr_t, Can be implicitly converted to any pointer .

So use null pointers as much as possible nullptr.

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