C++ – nothrow delete in C++

cmemory-managementvisual c++

This MSDN page mentions that there're nothrow versions of new and delete. nothrow new is quite a known thing – returns null instead of throwing an exception if memory allocation fails. But what is nothrow delete mentioned there?

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They are probably referring to the raw memory allocation functions operator new and operator delete.

When you invoke a specific version of placement new-expression (i.e. new-expression with extra parameters; they all are officially referred to as placement forms of new) and the memory allocation function operator new succeeds, but the process fails later for some other reason (the constructor throws), the implementation has to abort the process and automatically release the allocated memory by calling the appropriate version of operator delete. "Appropriate version" of operator delete in this case is the version that has the same set of parameters as the operator new function previously used for memory allocation (except for the very first parameter, of course).

This applies to nothrow version of operator new as well. When you use a nothrow form of new-expression, it calls a nothrow version of operator new and then constructs the object in the allocated memory. If the constructor fails (throws), the implementation of the new-expression releases allocated memory with the help of nothrow version of operator delete. This is basically the only reason for this version of operator delete to exist.

In other words, the nothrow version of operator delete exists for very specific internal purposes. You should not normally want to call it yourself and, maybe, you don't really need to know about its existence. However, it is worth knowing that for the reasons described above, whenever you create your own version of operator new with extra parameters, it is always a good idea to provide a matching version of operator delete with the same set of extra parameters.

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C++ – the difference between #include and #include “filename”

In practice, the difference is in the location where the preprocessor searches for the included file.

For #include <filename> the preprocessor searches in an implementation dependent manner, normally in search directories pre-designated by the compiler/IDE. This method is normally used to include standard library header files.

For #include "filename" the preprocessor searches first in the same directory as the file containing the directive, and then follows the search path used for the #include <filename> form. This method is normally used to include programmer-defined header files.

A more complete description is available in the GCC documentation on search paths.

C++ – What are the differences between a pointer variable and a reference variable in C++

A pointer can be re-assigned:

int x = 5;
int y = 6;
int *p;
p = &x;
p = &y;
*p = 10;
assert(x == 5);
assert(y == 10);

A reference cannot be re-bound, and must be bound at initialization:

int x = 5;
int y = 6;
int &q; // error
int &r = x;

A pointer variable has its own identity: a distinct, visible memory address that can be taken with the unary & operator and a certain amount of space that can be measured with the sizeof operator. Using those operators on a reference returns a value corresponding to whatever the reference is bound to; the reference’s own address and size are invisible. Since the reference assumes the identity of the original variable in this way, it is convenient to think of a reference as another name for the same variable.
```
int x = 0;
int &r = x;
int *p = &x;
int *p2 = &r;

assert(p == p2); // &x == &r
assert(&p != &p2);
```

You can have arbitrarily nested pointers to pointers offering extra levels of indirection. References only offer one level of indirection.

int x = 0;
int y = 0;
int *p = &x;
int *q = &y;
int **pp = &p;

**pp = 2;
pp = &q; // *pp is now q
**pp = 4;

assert(y == 4);
assert(x == 2);

A pointer can be assigned nullptr, whereas a reference must be bound to an existing object. If you try hard enough, you can bind a reference to nullptr, but this is undefined and will not behave consistently.

/* the code below is undefined; your compiler may optimise it
 * differently, emit warnings, or outright refuse to compile it */

int &r = *static_cast<int *>(nullptr);

// prints "null" under GCC 10
std::cout
    << (&r != nullptr
        ? "not null" : "null")
    << std::endl;

bool f(int &r) { return &r != nullptr; }

// prints "not null" under GCC 10
std::cout
    << (f(*static_cast<int *>(nullptr))
        ? "not null" : "null")
    << std::endl;

You can, however, have a reference to a pointer whose value is nullptr.

Pointers can iterate over an array; you can use ++ to go to the next item that a pointer is pointing to, and + 4 to go to the 5th element. This is no matter what size the object is that the pointer points to.
A pointer needs to be dereferenced with * to access the memory location it points to, whereas a reference can be used directly. A pointer to a class/struct uses -> to access its members whereas a reference uses a ..
References cannot be put into an array, whereas pointers can be (Mentioned by user @litb)
Const references can be bound to temporaries. Pointers cannot (not without some indirection):
```
const int &x = int(12); // legal C++
int *y = &int(12); // illegal to take the address of a temporary.
```
This makes const & more convenient to use in argument lists and so forth.

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C++ – the difference between #include and #include “filename”

C++ – What are the differences between a pointer variable and a reference variable in C++

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