C++: Difference between revisions

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===String===

<code>#include <string></code>

If you don't need to own the string, prefer to use <code>string_view</code>.

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[https://insanecoding.blogspot.com/2011/11/how-to-read-in-file-in-c.html Reference and comparison of different methods]

#include <cerrno>

#include <fstream>

#include <string>

#include <~~cerrno~~>

#include <string_view>

std::string get_file_contents(~~const~~ std::~~string &~~filename)

std::string get_file_contents(std::string_view filename) {

{

std::ifstream in(filename, std::ios::in | std::ios::binary);

if (in.good())

if (in.good()) {

{

std::string contents;

in.seekg(0, std::ios::end);

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Smart pointers were added in C++11.

There are 3 types of smart pointers:

* ~~<code>unique_ptr<~~/~~code>~~

* [https://en.cppreference.com/w/cpp/memory/unique_ptr <code>std::unique_ptr</code>] - one piece of code ''owns'' the memory at any given time.

* <code>shared_ptr</~~code>~~

* <code>std::shared_ptr</code> - the memory has multiple owners.

* <code>weak_ptr</~~code>~~

* <code>std::weak_ptr</code> - a non-owning reference to a shared_ptr.

~~Use~~ <code>unique_ptr</code> ~~when~~ one piece of code ''owns'' the memory at any given time.

~~Use~~ <code>shared_ptr</code> ~~when~~ multiple ~~objects need to reference the same thing~~.~~ ~~

In general, there should be one object owning an object using a <code>unique_ptr</code>. Whenever you pass the value around, other functions should receive the object as a reference making it clear that they do not have ownership of the object. Smart pointers are nullable and assignable similar to regular pointers.

~~Use~~ <code>weak_ptr</code> to ~~avoid cyclic dependencies which cause issues with reference counting~~.

If you ~~are using C++14 or newer~~, ~~you~~ should use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.

Prefer to use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.

~~Alternatively if you already have a smart pointer, you~~ can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.

You can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.

Example:

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===absl===

https://github.com/abseil/abseil-cpp is a library used by Google which supplements the standard library.

Useful things:

# <code>absl::Time</code> and <code>absl::Duration</code>.

# [https://abseil.io/docs/cpp/guides/strings#abslstrcat absl strings]

# [https://abseil.io/docs/cpp/guides/logging absl logging]

Many parts of absl now have <code>std::</code> equivalents such as <code>std::unique_ptr</code>, <code>std::string_view</code>, <code>std::span</code>. Unless contributing to Google codebases, you should probably prefer those.

At Google, they prefer absl hash containers over unordered_set and unordered_map:

# <code>absl::flat_hash_map</code>

==References==

[[Category:Programming languages]]

@@ Line 81: / Line 81: @@
 ===String===
 <code>#include <string></code><br>
+If you don't need to own the string, prefer to use <code>string_view</code>.
 <syntaxhighlight lang="cpp">
@@ Line 189: / Line 191: @@
 [https://insanecoding.blogspot.com/2011/11/how-to-read-in-file-in-c.html Reference and comparison of different methods]
 <syntaxhighlight lang="C++">
+#include <cerrno>
 #include <fstream>
 #include <string>
-#include <cerrno>
+#include <string_view>
-std::string get_file_contents(const std::string &filename)
+std::string get_file_contents(std::string_view filename) {
-{
    std::ifstream in(filename, std::ios::in | std::ios::binary);
-   if (in.good())
+   if (in.good()) {
-  {
      std::string contents;
      in.seekg(0, std::ios::end);
@@ Line 264: / Line 265: @@
 Smart pointers were added in C++11.<br>
 There are 3 types of smart pointers:
-* <code>unique_ptr</code>
+* [https://en.cppreference.com/w/cpp/memory/unique_ptr <code>std::unique_ptr</code>] - one piece of code ''owns'' the memory at any given time.<br>
-* <code>shared_ptr</code>
+* <code>std::shared_ptr</code> - the memory has multiple owners.
-* <code>weak_ptr</code>
+* <code>std::weak_ptr</code> - a non-owning reference to a shared_ptr.
-Use <code>unique_ptr</code> when one piece of code ''owns'' the memory at any given time.<br>
-Use <code>shared_ptr</code> when multiple objects need to reference the same thing.<br>
+In general, there should be one object owning an object using a <code>unique_ptr</code>. Whenever you pass the value around, other functions should receive the object as a reference making it clear that they do not have ownership of the object. Smart pointers are nullable and assignable similar to regular pointers.
-Use <code>weak_ptr</code> to avoid cyclic dependencies which cause issues with reference counting.<br>
-If you are using C++14 or newer, you should use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.<br>
+Prefer to use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.<br>
-Alternatively if you already have a smart pointer, you can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.
+You can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer.
 Example:
 <syntaxhighlight lang="cpp">
@@ Line 767: / Line 769: @@
 ===absl===
 https://github.com/abseil/abseil-cpp is a library used by Google which supplements the standard library.
+Useful things:
+# <code>absl::Time</code> and <code>absl::Duration</code>.
+# [https://abseil.io/docs/cpp/guides/strings#abslstrcat absl strings]
+# [https://abseil.io/docs/cpp/guides/logging absl logging]
+Many parts of absl now have <code>std::</code> equivalents such as <code>std::unique_ptr</code>, <code>std::string_view</code>, <code>std::span</code>. Unless contributing to Google codebases, you should probably prefer those.
+At Google, they prefer absl hash containers over unordered_set and unordered_map:
+# <code>absl::flat_hash_map</code>
 ==References==
 [[Category:Programming languages]]