====== C++ Notes and Information ======

Helpful tutorials on YouTube are by TheChernoProject https://www.youtube.com/channel/UCQ-W1KE9EYfdxhL6S4twUNw

(Too much of a beginner) Trying course from https://www.youtube.com/watch?v=vLnPwxZdW4Y


===== include =====

Includes library of code, either from local (name is in double-quotes) or in the language-provided libraries (name is in angle-brackets).

<code c++>
#include <iostream>
</code>

Use angle brackets for built-in libraries.

===== using namespace =====

<code c++>
using namespace std;
</code>

Places this code into the std namespace. That way, we can use ''cout'' instead of ''std::cout''. However, I don't use this namespace because TheCherno says not to, instead, always give explicit namespace value.

===== Linker =====

The C++ compiler creates and Object file, but separately. The Linker puts them together.

===== Pointers =====

https://www.youtube.com/watch?v=DTxHyVn0ODg&list=PLlrATfBNZ98dudnM48yfGUldqGD0S4FFb&index=16

A pointer is an integer which stores a memory address. Types have nothing to do with that.


The value 0 is not a valid memory address. It means 0

<code c++>
int main()
{
   // void* ptr = 0; // or   void* ptr = nullptr;
   int var = 8;
   // Where are you in memory
   int* ptr = &var; // Get the location of var, and put it into ptr as an integer pointer.
   
   *ptr = 9; // int value pointed at by pointer "ptr"
   
   std::cin.get();
}
</code>

<code c++>
int main()
{
   char* buffer = new char[8];// This uses heap
   memset(buffer, 0, 8);
   
   char** ptr = &buffer;// Pointer to a pointer
   
   delete[] buffer;// delete afterward to be nice
   
   std::cin.get()
}
</code>


===== Reference =====

Pointers and references are about the same thing. How we write them is different. References are syntax sugar on top of a pointer.

References reference an existing variable.

<code c++>
int main()
{
   int a =5;
   int& ref = a;// the & is part of the int defintion
   // We have created an alias. It is not really a variable.
   // We can use ref as though it is "a"
   
   ref = 2;
   std::cout(ref);
}
// Works, but this is clumsy

void Increment (int* value)
{
   (*value)++;// Value at the pointer "value"
}
int main()
{
   // We want to pass the memory address.
   int a = 5;
   Increment(&a);
   LOG(a);
}

</code>
<code c++>
// Use a reference instead of a pointer

void Increment(int& value)
{
   value++;
}
int main()
{
   int a = 5;
   Increment(a);
   LOG(a)
}

</code>


===== Memory =====

There are two areas of memory, Stack, and Heap.

^Stack|When scope for variable ends, the memory is freed.|

^Heap|Stays there until manually removed with ''delete''|


===== new keyword =====

The ''new'' keyword allocates memory from the Heap. It returns a pointer to it. The number of bytes to allocated is determined by the argument. ''int'' provides 4 bytes, for example. 

<code c++>
int * a = new int;

*a = 2;

std::cout << *a << std::endl;
</code>

<code c++>
int * a = new int;
// is nearly identical to this:
int * a = malloc(4);
</code>

===== Visual Studio Formatting/Indenting C++ code =====

Use Control-K, followed by Control-F.
7/5/2019

===== Separate Classes into Headers and CPP files =====

C++ classes (and often function prototypes) are normally split up into two files.  The 
header file has the extension of .h and contains class definitions and functions. The 
implementation of the class goes into the .cpp file. By doing this, if your class 
implementation doesn’t change then it won’t need to be recompiled....

{{ :programming:cplusplus:separatecompilation.pdf |}}

====== Difference between Dot and Arrow ======

Use Arrow when the value on the left is a pointer, use a dot when it is a class instance.

To access members of a structure, use the dot operator. To access members of a structure through a pointer, use the arrow operator. [[https://www.tutorialspoint.com/cplusplus/cpp_member_operators.htm|Details]]

====== Troubleshooting while Building ======

Sometimes the *.h.gch will get corrupted or contain outdated information, so deleting that file and compiling it again should fix it. [[https://stackoverflow.com/questions/1241399/what-is-a-h-gch-file|Details]]