Do Not Check For nullptr Explicitely In Examples (closes #1142) (#1144)

CppCoreGuidelines.md

@@ -1015,10 +1015,10 @@ Time and space that you spend well to achieve a goal (e.g., speed of development
 
     X waste(const char* p)
     {
-        if (p == nullptr) throw Nullptr_error{};
+        if (!p) throw Nullptr_error{};
         int n = strlen(p);
         auto buf = new char[n];
-        if (buf == nullptr) throw Allocation_error{};
+        if (!buf) throw Allocation_error{};
         for (int i = 0; i < n; ++i) buf[i] = p[i];
         // ... manipulate buffer ...
         X x;
@@ -1499,7 +1499,7 @@ Ideally, that `Expects(x >= 0)` should be part of the interface of `sqrt()` but
 
 ##### Note
 
-Prefer a formal specification of requirements, such as `Expects(p != nullptr);`.
+Prefer a formal specification of requirements, such as `Expects(p);`.
 If that is infeasible, use English text in comments, such as `// the sequence [p:q) is ordered using <`.
 
 ##### Note
@@ -3214,7 +3214,7 @@ Consider:
 
     int length(Record* p);
 
-When I call `length(p)` should I test for `p == nullptr` first? Should the implementation of `length()` test for `p == nullptr`?
+When I call `length(p)` should I check if `p` is `nullptr` first? Should the implementation of `length()` check if `p` is `nullptr`?
 
     // it is the caller's job to make sure p != nullptr
     int length(not_null<Record*> p);
@@ -3301,7 +3301,7 @@ Consider:
 
     int length(const char* p);
 
-When I call `length(s)` should I test for `s == nullptr` first? Should the implementation of `length()` test for `p == nullptr`?
+When I call `length(s)` should I check if `s` is `nullptr` first? Should the implementation of `length()` check if `p` is `nullptr`?
 
     // the implementor of length() must assume that p == nullptr is possible
     int length(zstring p);
@@ -3389,7 +3389,7 @@ Sometimes having `nullptr` as an alternative to indicated "no object" is useful,
 
     string zstring_to_string(zstring p) // zstring is a char*; that is a C-style string
     {
-        if (p == nullptr) return string{};    // p might be nullptr; remember to check
+        if (!p) return string{};    // p might be nullptr; remember to check
         return string{p};
     }
 
@@ -3422,7 +3422,7 @@ Returning a `T*` to transfer ownership is a misuse.
 
     Node* find(Node* t, const string& s)  // find s in a binary tree of Nodes
     {
-        if (t == nullptr || t->name == s) return t;
+        if (!t || t->name == s) return t;
         if ((auto p = find(t->left, s))) return p;
         if ((auto p = find(t->right, s))) return p;
         return nullptr;
@@ -5022,7 +5022,7 @@ Leaving behind an invalid object is asking for trouble.
         X2(const string& name)
             :f{fopen(name.c_str(), "r")}
         {
-            if (f == nullptr) throw runtime_error{"could not open" + name};
+            if (!f) throw runtime_error{"could not open" + name};
             // ...
         }
 
@@ -10649,7 +10649,7 @@ Requires messy cast-and-macro-laden code to get working right.
         for (;;) {
             // treat the next var as a char*; no checking: a cast in disguise
             char* p = va_arg(ap, char*);
-            if (p == nullptr) break;
+            if (!p) break;
             cerr << p << ' ';
         }
 
@@ -11872,7 +11872,7 @@ There are many approaches to dealing with this potential problem:
 
     void f1(int* p) // deal with nullptr
     {
-        if (p == nullptr) {
+        if (!p) {
             // deal with nullptr (allocate, return, throw, make p point to something, whatever
         }
         int x = *p;
@@ -11887,7 +11887,7 @@ There are two potential problems with testing for `nullptr`:
 
     void f2(int* p) // state that p is not supposed to be nullptr
     {
-        assert(p != nullptr);
+        assert(p);
         int x = *p;
     }
 
@@ -11895,7 +11895,7 @@ This would carry a cost only when the assertion checking was enabled and would g
 This would work even better if/when C++ gets direct support for contracts:
 
     void f3(int* p) // state that p is not supposed to be nullptr
-        [[expects: p != nullptr]]
+        [[expects: p]]
     {
         int x = *p;
     }
@@ -15453,7 +15453,7 @@ In such cases, "crashing" is simply leaving error handling to the next level of
     {
         // ...
         p = static_cast<X*>(malloc(n, X));
-        if (p == nullptr) abort();     // abort if memory is exhausted
+        if (!p) abort();     // abort if memory is exhausted
         // ...
     }
 
@@ -19440,7 +19440,7 @@ Of course many simple functions will naturally have just one `return` because of
 
     int index(const char* p)
     {
-        if (p == nullptr) return -1;  // error indicator: alternatively "throw nullptr_error{}"
+        if (!p) return -1;  // error indicator: alternatively "throw nullptr_error{}"
         // ... do a lookup to find the index for p
         return i;
     }
@@ -19450,7 +19450,7 @@ If we applied the rule, we'd get something like
     int index2(const char* p)
     {
         int i;
-        if (p == nullptr)
+        if (!p)
             i = -1;  // error indicator
         else {
             // ... do a lookup to find the index for p
@@ -20033,7 +20033,7 @@ Use `not_null<zstring>` for C-style strings that cannot be `nullptr`. ??? Do we
 These assertions are currently macros (yuck!) and must appear in function definitions (only)
 pending standard committee decisions on contracts and assertion syntax.
 See [the contract proposal](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0380r1.pdf); using the attribute syntax,
-for example, `Expects(p != nullptr)` will become `[[expects: p != nullptr]]`.
+for example, `Expects(p)` will become `[[expects: p]]`.
 
 ## <a name="SS-utilities"></a>GSL.util: Utilities